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Doctoral Dissertations Student Theses and Dissertations

1971

Synthesis, X-ray characterization, structural and magnetic studies Synthesis, X-ray characterization, structural and magnetic studies

of a new class of iso-structural BiMO₃ compounds of a new class of iso-structural BiMO compounds

Joseph Donato Bucci

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SYNTHESIS, X-RAY CHARACTERIZATION, STRUCTURAL

AND MAGNETIC STUDIES OF A NEW CLASS OF

ISOSTRUCTURAL B~Mo3 COMPOUNDS

by

JOSEPH DONATO BtJ CCI, 19it4-

A DISSERTATION

Presented to the Faculty of the Graduate School of tbe

UNIVERSITY OF MISSOURL-ROLLA

In Part~a1 Fu1f~11ment of the Requ~rements for the Degree

DOCTOR OF PHILOSOPHY

~~~lM,o LA~O 8~4<

1.n

CHEMISTRY

1971

@ 1972

JOSEPH DONATO BUCCI

ALL RIGHfS RESERVED

PLEASE NOTE:

Some pages have indistinct print. Filmed as received.

UNIVERSITY MICROFILMS.

ii

PUBLICATION OPTION

Th~s d~ssertat~on has been prepared ~n the style ut~l~zed by

the journal Acta Crysta11ographica. Pages 1-14 have been subm~tted

to that journal for publ~cat~on. Pages 15-95 will be subm~tted

for publ~cat~on ~n the near future. Append~ces A, B, and C have

been added for clar~f~cat~on of some of the results ~n the four

eect~ons of th~s d~ssertat~on.

iii

ABSTRACT

This dissertation consists of four sections. The first part

is a temperature dependent X-ray study or the lattice parameters

of B1Feo3

•

The synthesis and subsequent X-ray characterization of

BiCo3 , BiA103 , BiMn03 , BiSco3 , BiCo1_xFexo3

, and BiA11_xFexo3

are

reported in the second part. These compounds all crystallize in

the body centered cubic (BCC) structure with aN10.2i. Single

crystal Precession and Weissenberg photographs confirmed the BCC

structure.

In part three, the results of the magnetic studies on BiCoo3

and ~Al. 9 Fe. 1 o3

are presented. The magnetic data for BiCo03

are substantiated by X-ray thermal expansion studies.

In the last part the compound BiCo.9

Fe.1

o3 is examined in

some detail. The magnetic studies are substantiated by the X-ray

thermal expansion results.

iv

ACKNOWLEDGEMENTS

The g1ory and primary benefits of an advanced degree are

enjoyed by one man; yet, unselfishly, many help to bring about its

materialization. It is very difficult to individually thank every­

one that has contributed to the fulfillment of my graduate endeavors.

It would be neglectfully unjust however to omit thanking certain

people in particular.

Specifically, I thank Professor M. E. Straumanis for the use

of his X-ray equipment, and for helpful discussions and suggestions

during the early part of this work.

I sincerely thank Dr. J. s. Shah, a colleague and a friend.

His help with the low temperature x-ray work and the many discuss­

ions about this work ~11 not b~ forgotten.

I also wish to express my sincerest gratitude to Dr. R. Lemaire

(Visiting Professor, from C.N.R.S., Laboratoire Electroatatique

et Physique du Metal; Grenoble, France). His he1p in the Weissenberg

single crystal work and in the interpretation of the magnetic studies

has contributed to the completion of this work.

Above all others, I sincere1y thank my Major Advisors,Dr. W. J.

James, and Dr. B. K. Robertson. In their patience and wisdom, they

have a11owed me to choose the research projects, and then helped to

bring about the solutions. I thank them for their understanding

and guidance. Their friendship I shall always cherish.

Final.ly, I thank m:y parents and the rest of my family.

~thout them I would be nothing. J. D. Bucci

16 August 1971

v

TABLE OF CONTENTS

Page

PU'BLICATION OPriON ................................................. ii

.ABSTRACT • ............................................................... iii

ACKNO'WLEDGEJvt.ENT • ••••••••••• ., •••••••••••••••••••••••••••••••••••••• i v

LIST OF ILLUSTRATIONS ••••••••••••••••••••••••••••.••.•.•••.•.•..• vii

LIST OF TABLES ....................................................... 1x

PART I:

THE PRECISION DETERMINATION OF THE LATTICE PARAMETERS AND

THE COEFFICIENTS OF THERMAL EXPANSION OF Bi.Fe03

Abstract . ................................................. 1

Introduction ..•..••..•••........•....•................... 1

Experimental . .•••••••••••...•..•......•.................. 2

Results and Di.scussion ..................................... 3

Conc1ueion . ..•••••••••..•.......•••.•.... e •••••••••••••• 12

References . .............................................. 14

PART II:

THE SYNTHESIS AND OF BiM0

3 MAGNETIC

X-RAY CHARACTERIZATION OF A NEW CLASS COMPOUNDS

Abstract . .•••.•.•..•....•.•.••...•.....•..•....•.•...... 1 5

Introduction . ............................................. 1 5

Experimental . .•••.•••••••.••••..••..•......•.•.•.•.•.... 1 7

Resu1 ts and Discussion • .................................. 1 8

Conc1usion ••••••••••••••••••••••••••••••••••••••••••••.• 39

References ••••••••••••••••••••••••••••.••••••••••••••••• 42

PART III

MAGNETIC AND X-RAY STUDIES OF THE ISOSTRUCTURAL

BiCo03

AND BiA1. 9 Fe .l o3

SYSTEMS

vi

Table of Contents (continued) Page

Abstract ••••••••••••••••••••••.••••••••••••••••••••••••• 43

Introduction •••••.••.•.•.•••••.•.•.•••••.•.•.•••.•.••.•. 43

Experi.men tal ............................................. 44

Results and Discuss~on ••••••••••••••••••••••••.••••••••• 45

Cone 1usi..on •••••••••••••••••••••••••••••••••••••••••••••• 57

References ••••••••••••••••••••••••••••••••••••.•••••.••• 6o

PART IV

MAGNETIC TRANSITIONS IN BiCo.9

Fe.1

o3

Abstract •••••••••••••••••••••••••••••••••••••••••••••••• 61

Introducti.on •••••••••••••••••••••••••••••••••••••••••••• 62

Exper1.men tal •••••••••••••••••••••••••••••••••••••.•••••• 63

Results and Discussion •••••••••••••••••••••••••••••••••• 63

Conc1usi..on •••••••••••••••••••••••• * ••••••••••••••••••••• 94

References •••••••••••••••••••••••••••••••••••••••••••••• 95

VITA •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 96

APPENDICES

A. Latt:Lce Parameters of B:iFe03

as a funct:Lon of T(°C). .... ,97

B. Latt:Lce Parameters of Bi.Coo3

as a :funct~on of T(°K) • • • • • • 98

c. Latt:Lge Parameters of B~Co 9

Fe .1 03 as a function

ofT( K) •••••••••••••••••• : •••••• . . . . . . . . . . . . . . . . . . . ••••• 99

vii

LIST OF ILLUSTRATIONS

Pac;e

PART I

Temperature dependence of lattice parameters- BiFe03 ....•... 8

Splitting of the 10•4 and 11•0 reflections as a runct:1on 0 f temperature •••••.•••••••••.•.• ................... 11

PART II

Latti3~ parameter (a) of cubic phase vs. concentration or co ( Xc· 3+) .............................................. 25

0

BiCo1

Fe 0 , Amount of the cubic (BCC) phase "'X X --:_'5

formea as a ro:rtction of x .• ~ ................................. 27

BiCo.9

Fe 1 o3

, Zero Level (Precession) representation . * • ( 0) of the reciprocal lattice in the b c plane 1.9 ••••••••• 30

BiCo 9

Fe. 1 o3

, Zero Level (Precession) representation

of tte reciprocal lattice (91.9°) ••••••••••••••••••••••••••• 32

BiCo.9

Fe.l o3

, First Level (P~ecession) representation

of the reciprocal lattice (1.9 ) •••••••••••••••••••••••••••• 34

BiCo. 9 Fe·l o3 , First Level (Pr~cession) representation

of the rec procal lattice (91.9 ) ••••••••••••••••••••••••••• 36

BiCo.5

Fe.5

o3

, Zero Level (Weissenberg) representation

of the reciprocal lattice ••••••••••••••••••••••••••••••••••• 38

PART III

1 ( -1 BiAl 9

Fe.l o3 , Rec~procal Molar Susceptibility X mole )

vs. 'l'emperature T ( K) • •••••••••••••••••••••••••••••••••••• • 47

BiAl.9

Fe.l o3

, Magnetization (H) vs. Field (H). •••••••.•••• 49

1 ( -1 BiCoo

3, Reciprogal Molar Susceptibility X mole ) vs.

Temperature T ( K) • •••••••••••••••••••••••••••••••••••.••••• 53

BiCoo3

, Magnetization (M) vs. Field (H) ••••••••••••••••••••• 55

0 BiCoo

3, Lattice parameter~· vs. Temperature T ( K) •••••••.• 59

Viii.

List of Illustrations (continued) Page

PART IV

H(Oe) (Gauss), 0

vs. H T = 112.0 K •••••••••••••••••••••••••••• 66

M(Oe) (Gauss), 0

vs. H T = 124.21 K ••••••••••••••••••••••••••• 68

M(Oe) (Gauss), 0

vs. H T = 137.03 K ••••••••••••••.•••••••••.•• ?O

M(Oe) (Gauss), 0

vs. H T = 149.1 K •••••••••••••••••••••••••••• 72

M(Oe) (Gauss), 0

vs. H T = 162.24 K •• •••• ••••••••••••••••••••• 74

M(Oe) (Gauss), 0

vs. H T = 183.7 5 K ••••••••••••••••••••••••••• 76

M(Oe) vs. H (Gauss), T = 205.56°K ••••••••••••••••••••.•••••• 78

M(Oe) vs. H (Gauss), T = 0 239. 0 K •••••••••••••••••••••••••••• 80

M(Oe) vs. T (OK) H = 3000 Gauss ••••••••••••••••••••••••••••• 83

M(Oe) vs. T (OK) H = 4000 Gauss ••••••••••••••••••••••••••••• 85

M(Oe) vs. T (OK) H = 7000 Gauss ••••••••••••••••••••••••••••• 87

Lattice parameter a vs. T (OK). •••••• •• ••• • • • • ••• • •• • • • • • • •• 89

0 Spontaneous Magnetization Mo vs .• T ( K) ••••••••••••••••••••• 91

ix

LIST OF TABLES

PART I Page

Table I- BiFe03

- Thermal Expansion Coefficients ••••••••••.• 13

PART II

Table I - Reaction Conditions and Results for BiMo3

Co m_poun ds ................................ " •••••• " ................ 1 9

Table II- BiCo.5

Fe.5

o3 (interplanar d apacing) ••••••••••.• 20

Table III- Resistivity of BiCol-x Fax o3 •.••••...•.......... 40

THE PRECISION DETERMINATION OF THE LATTICE PARAMETERS

AND THE COEFFICIENTS OF THERMAL EXPANSION OF B~Feo3

ABSTRACT

1

The 1att~ce parameters or B~Feo3 were determ~ned employ~ng the

0 Straumanis method. At 25.13! 0.02 c, the hexagona1 parameters are

~ • 5.5799 ± 0.0003 i, and ch = 13.8670 ! 0.0005 i. The temperature

dependence or the 1att~ce parameters ~n the range 20-325°C ~s given

by the equat~ons: ~ = 5.5764 i + 6.06 x 10-5 t, and ch • 13.8620 i +

2.10 x 10-4 t. In the range or 344-838°C, the 1att~ce parameters

obey the fo11owing equat~ons: ~ = 5.5946 + 6.83 x 10-5 t, and

Ch = 13.7251 + 9.05 X 10-4 t - 12.503 X 10-7 t2 + 9.40 X 10-

10 t 3

- 3.57 x 1o-13 t 4 • By extrapo1at~on or the splitt~ng of the 11•0

and the 10•4 rer1ect~ons, the e1ectr~ca1 Cur~e temperature was

deter~ned to be 845 t 5°C.

INTRODUCTION

Dur~ng the past decade much attent~on has been devoted to the

perov~te-~ke BiFe03

; however, there seems to be considerable disagree­

ment amongst the various invest~gators concerning the latt~ce para-

meters, the~r temperature dependence, and the number and nature or the

phaae transit~ons which have been reported.

Previous ~nveetigators have reported the latt~ce parameters of

bismuth ferrite either from pre~minary measurements on sing1e

crystals (M1che1 1 Moreau, Achenbach, James, and Gerson, 1969) or from

2

measurements of ref'l.ections w:l th e << 70°. (Zasl.avsk:li and Tutov •

v

1960; Tomashpol. 1 ak:li, Skor:lkov. Venevtsev. and Speranskaya. 1966).

In stud:les of' the temperature dependence of the various parameters

of BiFeo3

, there have been a number of confl.icting reports. Some

investigators report no anomal.ies associated w:Lth transitions (Fedul.ov

et al.., Venevtaev, Zhdanov, and Smozhevskaya, 1961; Fedul.ov, 1962),

whil.e others (Kran:Lk, et al.., Khuchua, Zhdanova. and Evseer, 1966;

Isma:Ll.zade, 1967) report as many as seven or eight trans:Lt:Lons in

the te•perature range 0.870°c.

In an attempt to cl.arify some of the e:x:S.ating amb:lgu:Lties and

di.screpanc:Les, we per.tormed a careful. ¥-ray study of' the BiFeo3

system

in the temperature range 20-86o0 c. The methods empl.oyed and the

resul.ts of' our ef'.torts are reported in th:ls articl.e.

EXPERIMENTAL

The sampl.e used in this investigation was prepared in the manner

previousl.y reported by Achenbach, James, and Gerson (1967). In the

0 temperature range 20-60 c, powder photographs were obtained by use

of' a strauman:Ls asymmetric camera. The sampl.e was mounted on a gl.ass

.tiber l.ess than 0.2 mm in d:lameter, and the temperature was control.l.ed

0 0 wi.thi.n t 0.02 c. In the temperature range .from 100-860 c, a Seemann

high temperature camera was empl.oyed. The temperature was control.l.ed

0 w:Lth:ln t 4 c. A Pt-Pt 10% Rh thermocoupl.e calibrated against the

mel.t:Lng points or B:L, Sb, Au, and Sn was used to measure the temper-

atures.

To m:lnim:lze decomposition at higher temperatures, the sampl.e was

initial.l.y pl.aced in a quartz capil.lary which was subsequently seal.ed

under vacuum. Unfortunate1y, this method proved to be unsatis.tactory

3

above 600°C. Because or a "spotty" photograph at 65Q°C, the capi.llary

was broken and exam1ned under a mi.croscope. The i.nner wa11 revealed

an "etched" surface suggesting reacti.on or B1.Feo3

w1. th the quartz.

To circumvent this d1..ff:i.cu1ty, a plati.num wi.re ("fiber") wi.th a

diameter of appro~mately 0.25 mm was used as a sample mount at the

h:f.gher temperatures. The sample was mounted on the plati.num "£1. ber"

1.n a manner anal.ogous to the glass mount tor the Straumanis camera.

A1though the vase11.ne used to apply the powder to the plati.num under­

goes vaporizati.on and decompos1.t1.on, the matri.x of the sample remai.ns

intact. To determine whether the measurements made usi.ng the plati.num

mount were 1.n agreement wi.th those made usi.ng the quartz ca~11ary,

several of the lower temperature experi.ments were repeated usi.ng the

p1at1.num "f'ib•r". The results obtai.ned trom the two different types

or measurements agreed w:i.thi.n the experimental error 11.m1.ts.

Throughout thi.s 1.nvest1.gat1.on, Co-rad:i.ati.on was used. The

entire pattern was 1.ndexed on the basis of a hexagonal double cell.

The transformat1.on to the rhombohedral parameters can be realized

readily (Donnay and Takeda, 1963; International Tables for X-Ray

Crystallography, 1965).

For the determ1.nat1.on o£ the 1att1.ce parameters at all temperatures,

the well-resolved 20•1~ 1 , 40•1oa1

, and 42•aa1 li.nes were used i.n

order to attain maximum prec1.s1.on.

The 11.near least squares re£1.nement of the data was done on an

IBM/360 computer, employi.ng a program wri.tten by c. w. Ts1.mpr1.s.

RESULTS AND DISCUSSION

The study is divided 1.nto two parts: (a) the determ1.nat1.on of

the lattice parameters and their temperature dependence, and (b) the

number and nature of the phase trans~t~ons ~n the B~Feo3 system.

Fi~p1 ev, Smory~nov, Fesenko, and Ve1yaev (1960), ~ndexed

B~Feo3 on the bas~s of a rhombohedra11y d~storted un~t cell, ~th

aRh • 3.965 i•, and ~h e 89°28•. The measurements were made on

samp~es w~ch had been synthes~zed from the o~des at 600-725°C. v

4

Subsequent ~nvest~gators (Tomashpol'ski~, Venevtsev, and Zhadanov, v

1964; Ism~lzade, 1965; and Tomashpol's~~. et a1., 1966) arr~ved

at appro~mately the same parameters.

Zaslavski~ and Tutov (1960) who d~d most of the structural

analys~s ~n hexagonal coor~nates, reported the parameters as

~ • 5.581 i•, and ch = 6.934 i•.

On the bas~s of s~ngle crystal and neutron d~ffract~on data,

~chel, et al. (1969) concluded that ~D order to explain the super-

structure l~nes ~n B~F.o3 , a double cell had to be emp~oyed. They

reported the hexagonal. parameters "h = 5. 59 and ch = 13.7 i.

The ~rst attempt to dete~ne the Cu~e temperature of B~Feo3 was an X-ray and thermal anal.ys~s study by Fedulov, et al.. , ( 1961).

They reported no anomalies ~n the un~form ~ncrease ~n ~h' and the

constancy of ~h· In the thermal analys~s data, no trans~t~ons

were ev~dent below 850°C; hence, they concluded that the Cur~e po~nt

was above 850°C.

Fedulov (1962) ~nvest~gated the change ~n latt~ce parameters vs.

temperature us~ng ~ray methods ~n the range o.80o0 c. He reported

no anomal~es ~n the l~near ~ncrease in ~ with temperature and the

essent~ally constant ~h· In the same pub~~cat~on he reported the

*Converted from kX

5

study of the B~Feo3-PbTio3 system. From the behavior of the Curie

point in that system, he extrapolated to the composition 100% BiFeo3

and determined the Curie temperature to be 85Q°C.

Shortly thereafter, Fedulov, Venevtsev, Zhdanov, Smazhevskaya,

and Rez, (1962) investigated the system PbTio3

-BiFeo3

• In addition

to the X-ray study, they added conductivity measurements as a function

of temperature. Again by extrapolation to the compos~tion 100% BiFeo3

,

they determined the Curie temperature to be 850 ± 15°C.

Tomashpol'skii, Venevtsev, and Zhdanov (1964) studied the

temperature dependence of the rhombohedral parameters, the specific

0

magnetization, and the dielectric constant of BiFeo3

, from 0-800 c.

They reported that all of the parameters exhibited anomalies at about

0 ' 370 C (the Neal temperature).

A subsequent investigation by Roginskaya, Tomashpol'skii,

Venevtsev, Petrov, and Zhdanov (1966), on the dielectric and magnetic

properties of BiFeo3

and its solid solutions with PbFe.5

Nb.5

o3

,

0 also revealed anomalies in the parameters at about 370 c.

Because of the discrepancies that existed in the literature,

Kranik et al., (1966) did an exhaustive study of the temperature

dependence of the dielectric constant (e), the tangent of the

dielectric losses (5), and the dilatometric relative linear expansion

on "-practically one phase ••• " samples of BiFeo3

• In the range

0 20-850 c, they reported eight reversible phase transitions, along

with an irreversible transition at about 870°C. The transition at

0 845-850 C was assigned to the Curie point.

Finally, Ismailzade (1967) performed a detailed X-ray study of the

phase trans~tions in the BiFeo3

system. He reported transitions at

6

approximately the same temperatures as those reported by Kranik et at.,

(1966). However, Isma11zade claimed that the transition at 845-85Q°C

was not the Curie point transformation because the symmetry o! the

B1Feo3

cell did not become cubic as would be expected. Accord1ng to

"· •• the trend in the 2200, and 22oa1 lines for 800 ~ 835 -) 85Q°C",

he assigned the Curie temperature as 875-880°C. This seems to be an

unlikely conclusion, since at such temperatures BiFeo3

is completely

decomposed.

By using Co-radiation in the present work the a1

a 2 doublets of the

20•14, 40•10, and 42•2 reflections were easily resolved at angles

0 greater than 77 • The hexagonal parameters experimentally determined

0 at 25.13 C were found to be:

~ = 5.5779 t 0.0003 i

and

Transformation to the rhombohedral cell yields:

~h = 5.6336 t o.ooo3 i

~h = 59° 20.86 t 0.30 1

Although agreement With other investigators is reasonable, in

attempts to index the high angle lines, the discrepancies can cause

considerable confUsion because of the sm~1 differences in the d

spacings.

In t~s investigation, we round evidence for only two transitions.

0 The first transition (figure 1 • ) :Ln the range of 325-344 C, we

• attribute to the Nee1 temperature. Most other investigators report

0 a h:l.gher val.ue of 370 c.

7

Fi.gure 1

Temperature Dependence of Latt~ce Parameters B1Feo3

0 =

8

5.6300

5.61.50

5.6000

14.000

5.5700

0 300 600 900

9

0 As BiFeo

3 begins to slowly decompose at about 810 C and the film

exposure time increases to about twelve hours near 840°C, the three

doublets cou1d not be clearly resolved above 838°C. As a result,

the transition at the electrical Curie point could not be observed

directly in the back ref1ection region. However, the back reflection

0 doublets were reso1ved we11 enough at 838 C to a11ow a determination

of the 1attice parameters. Attempts to photograph the samp1e at

845-850°C or above yie1ded "spotty" photographs. Apparently, in the

region 835-860°C, a sma11 increase in temperature greatly accelerates

the decomposition process.

At about 810°C the approach of the rhombohedral structure

toward a cubic one was evidenced by the decrease in the splitting,

6, of the 11•0 and 10•4 1ines in the front ref1ection region. Since

the transformation at the Curie point could not be observed directly,

the decrease in sp1itting, 6 , was measured as a fUnction of tempera-

0 ture from 810-838 C (figure 2.). At the point where 6=0 (by extra-

po1ation), the transition we attributed to the electric Curie point

is comp1ete. The resu1ting value for T is 845 t 5°C. c

is in good agreement with others previous1y reported.

This value

The equations for the lattice parameters of BiFeo3

as a fUnction

0 of temperature in degrees C arez

Temperature range: 20-325°C

(a) ~ = 5.5764 i + 6.06 x lo-5 t ~deg- 1

Temperature range: 344-838°c

Figure 2

Splitting of the 10•4 and 11•0 reflections as

a function of temperature.

~ is in arbitrary units

1.0

0 . .5

o.o

r-------------------------------------------~

700 7.50

figure 2

\

' 8.50 900

11

(c)

(d)

12

= 13.7251 + 9.05 x 10-4 t i-deg-1 - 12.50 x 10-7 t 2 i-deg-2

+ 9.40 x 10-10 t 3 i-deg-3 - 3.57 x 1o-13 t 4 i.deg-4

The l.i.near coef':f'i.c:f.ents of' thermal expansion at constant

pressure are reported :in the form:

{e)

where

"t • l:f.near coef'f':l.c:f.ent of' thermal expans:f.on

x0

• lattice ~ameter at a re~erence temperature t0

~= d t

change :in lattice parameter w:ith respect to temperature at constant pressure

The l:f.near coe~f':f.c:f.ents of' thermal expansion of' B:f.Feo3

derived

from the exper:f.menta11y determ:f.ned equations a-d are recorded :in

table I.

The reference temperatures (t ) used :in equation e, are 25.13°C 0

0 :Ln the lower range, and 3 50 C :in the h:igh temperature range.

CONCLUSION

The thermal expansion of' B:i.Feo3

was investigated in the temP­

o erature range 20-860 K. From the results, it :is concluded that

B:f.Feo3

:is a ferroelectric up to its decomposition temperature.

13

TABLE I

B~Feo3 - Thermal Expansion Coefficients

t t ( OC) empera ure range

2.5.13 - 325 a ~

t: 10.86 X 10-6

a = 15.14 X 10-6 ch

344-838 ex = 12.21 X 10-6

~

a = 64.999 X 10-6 - 17.96

ch X 10-8 t d -1 eg + 20.25 X

10-11 t2 -2 10.25 X deg -10-14 t3 deg-3 •

14

REFERENCES

ACHENBACH, G. D., JAMES, W. J., and GERSON, R., J. A. Cerami.c Soc.,

2Q., 8 (1967).

DONNAY, J. D., and TAKEDA, H., Tables for Rhombohedral-Hexagonal

Transformations, Pub~ication of the Crystal~ographic Laboratory of

the Johns Hopkins University, Baltimore, Mary~and, U.S.A. (1963).

FEDULOV, S. A., Soviet Physics- Dokla?y, 6, 8 p. 729 (1962).

FEDULOV, S. A., VENEVTSEV, Yu. N., ZHDANOV, G. S., and SMAZHEVSKAY.A.,

E. G., Soviet Physics--Crystallography,£, 640 (1961).

FEDULOV, S. A., VENEVTSEV, Yu. N., ZHDANOV, G. S., SMAZHEVSKAYA, E. G.,

and REZ, I. s., Soviet Physics-Crystal~ography, z, 1 pp. 62-66 (1962).

FILIP•EV, V. s., SMOLYANINOV, N. P., FESENKO, E. G., and BELYAEV,

I. N., Kristal~ografiya, z, 6, p. 958 (1960).

ISMAILZADE, I. G., Soviet Physics-Doklady, !!t 9 PP• 747-748 (1967).

KRANIK, N. N., KHUCHUA, N. P., ZHDANOV, V. V., and EVSEEV, V. A.,

Soviet Physics-Solid State, ~~ 3, pp. 654-658 (1966).

MICHEL, C., MOREAU, J-M., ACHENBACH, G. D., GERSON, R., and JAMES,

w. J., So1id State Comm., z, 701 (1969).

ROGINSKAYA, Yu. E., TOMASHPOL•SKII, Yu., Ya., VENEVTSEV, Yu. N.,

PETROV, V. M., and ZHDANOV, G. s., Soviet Physics, JETP, Sl• 1 pp.

47-51 (1966). v

TOMASHPOLISKII, Yu. Ya. t VENEVTSEV, Yu. N., and ZHDANOV, G. S.,

J. Exptl. Theoret. Phys. (U.s.s.R.),~. 1921-1923 (1964).

TOMASHPOL•SKII, Yu. Ya., SKORIKOV, V. M., VENEVTSEV, Yu. N., and

SPERANSKAYA, E. I., Izvestiya Akademii Nauk SSSR Neorganicheskie

Materialy, 2, 4, pp. 7o7-711 {1966).

ZASLAVSKII, A. I., and TUTOV, A. G., Sovi.et Physics-Dokl.ady, .12,2,

4, pp. 1257-1259 (1960).

THE SYNTHESIS AND X-RAY CHARACTERIZATION OF

A NEW CLASS OF BiM03

MAGNEriC COMPOUNDS

ABSTRACT

15

The compounds B~Coo3 , B~Mno3 , B~Alo3 , BiCol-x Fexo3 and BiAll-x

Fexo3 have been synthesized and characterized by X-ray methods.

The compounds are ~sostructura1, crystall~z~ng ~n the body centered

cub~c (BCC) structure with lattice parameters a , of approximately c

10.2 i. S~ngle crystals of B~Coo3 , BiCo0

•9

Fe0 •1

o3

and Bieo0

•5

Fe0• 5

o3 have been grown. Precess~on and We~ssenberg photographs

conf~rm the BCC structure and restr~ct the poss~ble space groups

to I23

, I 2 3 and Im3.

1

INTROOOCTION

AB03

type compounds, where A ~s a heavy metal and B ~s generally

a trans~t~on metal, have been subjected to much investigat~on

dur~ng the past two decades. This close scru~t~ny results largely

from the very ~nterest~ng and technolo~cally ~mportant propert~es

possessed by the compounds. Dependent upon the nature of the con-

st~tuents A and B and the reaction conditions, a wide var~ation

~n electr~cal and magnetic properties can be att~ned. A thorough

review of the work done in this area has been g~ven by Skinner,

S. M. (1969).

One of the most widely studied of these compounds ~s b~smuth

orthoferr~te (B~Feo3). B~smuth orthoferrite has been the subject

of ~nvest~gat~on ~n this laboratory (Moreau, J.M., ~chel, c., and

16

James, W.J. (1970), Bucci, J.D., Robertson, B.K. and James, W.J.

(1971)), thus a study was undertaken on the possible preparation

of analogues of BiFeo3

• In the process of synthesizing the solid

solutions, BiM1_xFexo3

, pure BiM03

compounds were prepared. The

compounds synthesized appeared to bear no resemblance to compounds

of the same formula reported by other investigators. High pressure

equ~pment is lacking in this laboratory, and consequently all samples

were synthesized under atmospheric pressure. In some cases the

preparations were carried out in inert argon atmosphere to minimize

oxidation of M+3 to M3+n.

' ' Early work on BiM03

was done by I. Naray-Szabo in 1947. He

reported the synthesis and X-ray characterization of BiAl03

and

BiCr03

• Both systems were classified as tetragonal with a=?.61 R,

c = 7.94 i and a= 7.75 i,,c = 7.95 R for the alumi.num and chromium

compounds respectively.

Sugawara, F., Iida, s., Syono, Y. and Akimoto, S. (1965)

successfully synthesized BiCro3

and BiMno3

under high pressures

and found the compounds to be triclinic distorted perovskites. The

method of synthesis consisted of enc~osing the mixed oxides in a

graphite capsule and firing the mixture at about 700-800°C under

pressures of 35-55 kbar. For BiMn03

they reported the parameters

0 0 0 ' 0 '

a= c :: 3.93 A, b = 3.98 A, a = y = 91 25 , ~ = 90 55 . BiCro3 has

approximately the same parameters.

In the same year Bokov, V.A., Myl'nikova, I.E., Kizhaev, S.A.,

Bryzhina, M.F. and Grigoryan, N.A. (1965) also published the syn-

thesis, structure and magnetic properties or BiMno3

. Their compound

was synthesized from a melt of the composition "80 mole % Bi2

o3

0 The melt was slow-cooled from 1000 to

0 700 c, and " in addition to Bi.2o

3 • 2 Mn

2o

3, a small amount of

Bi Mn03

i.n the form of fine dendrites 11 was obtained. The para­

meters listed for the triclinic structure are a = c = 7.86 R, 0 0 • 0 '

b = 7. 98 A and a = 7 = 91 40 • IS = 92 24 •

Tomashpol'skii, Yu. Ya., Zubova, E. V., Burdina, K. P., and

Venevtsev, Yu. N. (1967) synthesized a number of BiM03

compounds

under high pressure. Tomashpol'skii, Yu. Ya., Zubova, E. V.,

17

Burdina, K. P., and Venevtsev, Yu. N. (1969) published more detailed

data on the same compounds in 1967. Two of the compounds in ques-

tion were BiCoo3

and BiSco3

, for which they concluded that under

0 " ordinary pressure and 600-800 c, specimens of these compounds

develope the pyrochl.ore structure," where BiCoo3

and BiSco3

have

face centered cubic structures with a= 10.52 and 10.78 ~ respec-

tively. Their X-ray diffraction studies were performed on powders,

but no diffraction data or d spacings were given in the paper.

They also reported that under a pressure of 60 kbar and T = 700°C

BiCoo3

transforms to a cubic perovskite with a = 4.228 ~- BiSco3

changes to a distorted triclinic perovskite at 70 kbar and 600°C

with lattice parameters a = c = 4.042 i, b = 4.127 i and a = 7 = 0 ' 0 •

90 41 , 13 = 91 52 •

EXPERIMENTAL

All samples reported in this article (except BiCoo3

) were

prepared by thoroughly ~xing the starting oxides Bi2o3

and M2o3

for approximately two hours and firing the resulting mixtures for

two hours at the appropriate temperatures (see Table I). BiCoo3

was prepared from Bi (N03

)3 · 5 H20 and Co(No3) 2 • 6 H20.

18

The hydrated nitrates were heated overnight to expel water (at

0 about 400 F) and the anhydrous mixture was subsequently fired at

750°C. All samples were air quenched and, after grinding to fine

powder, X-ray patterns were taken to determine the phases present.

The reacting powders, BiM03

, were melted, and upon slow coolin8

of the melt ( ~ 1 deg/min) single crystals of BiCoo3

, BiCo0

_9

Fe0

_1o3

and B~Co0 • 5Fe0 • 5o3 were obtained in fairly large quantities.

The lattice parameters were determined for the powder samples

by use of high angle, back-reflections collected on a Straumanis

camera. Space group determinations for single crystals of BiCo0 _sf~j?3

were accompl~shed on a precession camera while BiCo0

•5

Fe0_

5o

3 was

studied by use of a Weissenberg camera. The radiation used for all

powder work was CrKa1

; for the single crystal data, MoKa.

Approximate resistivities of BiCoo3

, BiCo0•9Fe0 • 1o3 and

BiCo0•5

Fe0 •5

o3

were measured at liquid nitrogen and room tem­

peratures.

RESULTS AND DISCUSSION

The compounds BiGoo3

, BiAlo3, BiMn0

3, BiSco3 , BiCo1_xFexo3

and BiA11

Fe o3

crystallize in a body-centered cubic structure -x x

(Table I) when prepared at the appropriate temperatures. The

lattice parameters are approximately the same (a~ 10.20 ~), there-

fore only one pattern is given in detail. The powder pattern is

that of BiCo0•

5Fe0 •

5o3 (Table II).

In the attempted synthesis of BiCro3

, single phase material

could not be obtained. Only two attempts are reported in Table I,

0 yet a number of reactions were tried at 50 intervals in the range

TABLE I

Reaction Conditions and Results for BiM03

Compounds

F:i.r:ing Starting Materials

Time Firin§ Atm. Phases (hrs) Temp( C)

B1.2o3

+co2o3

B1(N03

)3

+Co(N03

)2

B1.Coo3

(LT)

B:t2o

3+(1-x)Co2

o3

+xre2o

3

X : .05

X : .10

X = .5

X = .65

Bi203

+cr2o3

B1.2o3+cr2o

3

B:1203+Mn203

Bi2o

3+Hn

2o

3

B:1203+A1203

Bi203+AJ..203

Bi2a3

+.9Al2o3

+.1Fe2o3

Bi2a

3+.9Al2o

3+.1Fe2o

3

Bi2o

3+sc2o

3

2

2

2

2

2

2

2

4

4

2

2

2

2

2

2

2

750

575

750

750

750

750

750

975

975

750

900

575

750

575

750

800

Ai.r

Air

Air

Ai.r

Air

Ai.r

Ai.r

Ai.r

Ai.r

.Ai.r

Ai.r

Ai.r

Ai.r

Ai.r

Air

Bi.Coo3

(B)

B:i.Co03

(LT)

B1.Coo3

(B)

BiCo. 95Fe. 5

o3 (B)

Bi.Co • 9Fe • 1 o3 (B)

B:i.Co. 5Fe. 5o3

(B)

B1Co. 35Fe. 65o3(B)

BiCro3

+Cr 2o3

BiCr03

+cr2 o3

BiMn03

(B)

Bi2

Mn4o

9

B:i.AJ.03

(B)

Bi2Al

4o

9

BiAl. 9Fe • 1 o3 (B)

Bi 2 Al3 • 8Fe • 2 o9

BiSco3

(B)

19

a* db

10.1871

11.2

10.1871

10.1778

10.1779

10.1786

10.1790

11.3

11.3

10.22

0+

10.1813

+ 0

10.20.

* = Lattice parameters are not corrected for refraction

B = Body centered Cubic phase o+= Orthorhombic * = Values calculated from front reflections

LT = Low temperature cubic phase

20

TABLE II

Bi.Co. 5 Fe. 5 o3 (Cr K .

" = 2.2909) (X .

hk1 d(i) lobs hkl d(i) Iobs

2.2:.0 3.5786 w 631 1. 5002 M

310 3.2067 VS( 100) 444 1.4710 w

222 2.9277 MW 710,550,543 1.4399 w

321 2.7122 s 640 1 .4103 vvw

400 2 • .5029 M 633,721,552 1 .3850 w

411,330 2.3954 vw 642 1.3604 vw

420 2.2721 w 730 1 .3366 vw

332 2.1670 MW 732,651 1. 2930 vw

422 2.0748 MW 800 1 .2703 w

510,431 1.9947 MW 811,741,554 1 .2539 w

521 1 .8562 vw 820,644 1 .2348 vw

433,530 1. 7442 MS 653 1 • 2173 s

600,442 1. 6960 M 822,660 1.2002 s

611,532 1.6506 MS 831,750,743 1.1839 s

620 1.6014 w 662 1.1682 vvw

541 1. 5698 vw 752 1 • 1 531 w

622 1. 5351 vvw

VVW =very very weak M = med:lum (I = 50)

vw = very weak MS = medium strong

w =weak (I < 25) s = strong (I > 80)

MW = medium weak vs = very strong

21

0 600-1150 c. The reactions were car~ed out under argon atmosphere

to prevent Cr+3 from oxidizing to higher states. Reaction times

were v~ed from two hours to twenty-four hours. All attempts

fai.led to yield a single phase product. Leaching w1. th HN03

did

not improve the purity to any great extent. The BiCro3

phase can

be indexed on the basis of a cubic cell with a~ 11.25 i, yet it

is not isostructura1 wi.th the BCC compounds. Since it could not

be sufficiently purified, no further investigations were carried

out on BiCr03

•

The synthesis of BiCo03

was realized much more readily.

Although the usual ceramic techniques yield BiCoo3

after repeated

firings, it is much easier and faster to -.yathe~ze BiCoo3

by

using the nitrates as the starting materials. The process can be

described by the following equations:

Bi(N03

)3

• 5 H2

o 2350C> Bi(NO ) + 5 H2o t

a350C> Co(N03 )3 Co(N0

3) 2

• 6 H2

o + 6 H2o t 3 2

Bi(N03

)3

+ Co(N03 ) 2 -~> BiCo03

+ 5 NO+~ 02

5 NO+~ o2

In this reaction the temperature is a critical factor in deter-

mining the resulting phase. 0

Between 550 and 600 C a cubic phase

results. The X-ray pattern indicates that it is isostructural to

the B1Cr03

previously discussed. Slightly above 600°C BiCo03

begins to transform to the BCC structure (the structure which

results from the oxides). Since the transformation is irreversible

and the low temperature (LT) phase is a finely divided powder,

22

the possibilities of utilizing it (e.g., single crystals, solid

solutions, etc.) are somewhat limited. For these reasons no add-

itional investigations were made.

At 750°C the transformation from the low temperature phase to

body_centered cubic is complete. +2

To determine whether all Co

+3 was oxidized to Co in the process, the starting materials and the

final product were carefully weighed. Within experimental error

the theoretically expected amount of BiCoo3

was formed. In the

transformation from the LT phase to the BCC phase there was no

weight change.

The BCC forms of BiMn03

, BiA1o3

and BiAll-x Fex o3

were syn­

thesized at 700°C, 575°C and 600°C respectively. Slight increases

in reaction temperature causes the above compounds to pass irrevers-

ibly into the orthorhombic Bi2

M4

o9

structure reported by Niizeki,

N. (1966).

Since most of the BCC structures synthesized in this labora-

tory undergo the transformation to the orthorhombic phase while still

fine powders, one of the few possibilities of harnessing their phy-

sical properties would be to cold press them at fairly high pressures.

Such pellets are fragile, thus their uses would be limited.

BiCoo3

and its solid solutions BiCo1

Fe 03 are very stable -x x

to about 1300°C, although all melt in the range 0

780-800 c. If

there are transformations in the molten state, they appear to be

reversible.

The ions Fe+3 and Co+3 have similar ionic radii and electronic

configurations, therefore it would at first glance seem possible

to substitute Co+3 for Fe+3 , and vice versa, over the entire range

of x in BiCo 1 Fe o3

• Substitution was attempted in the range -x x

23

from x = 0 to x = 0.98. From x ~ 0.98 to x = 0.66 two phases result,

namely the rhombohedral (BiFeo3

) and the body-centered cubic. The

amount of each phase present did not correspond to the percentages

of the starting oxides. The phase diagram thus is not a simple two

component system (a+ ~) with a eutectic (y). If the system were

truly a two-phase system, the lattice parameters of a and ~. which

would correspond to BiCoo3

and B~Feo3 , should be independent of

concentrat~on. The above statement of course presupposes thermo-

dynamic equ~l~brium.

Figure 1 clearly shows that the lattice parameters do vary

W1th concentration. The lattice parameters of the cubic phase in­

creases ~th an increase in concentration of Co+3 up to x = 0.64,

after which the rhombohedral phase disappears. These data seem to

indicate that the cubic phase is continually changing by some small

amount such that the composition of the BCC phase in the two-phase

region is better represented by BiCo 1 Fe o

3.

-Y y

The competition of Co+3 with Fe+3 even at very low concentra-

tions of Co+3 (x = 0.98, 0.95, 0.90) forces Fe+3 to substitute into

the BCC structure. It appears from our results that Co+3 does not

substitute for Fe+3 at low eo+3 concentrations. A semiquantitative

determination of the concentrations of each of the two phases

present was made by comparing the I = 100 reflection for each phase

as measured !rom the resulting X-ray patterns. The results are

plotted in figure 2. One interesting mechanical property of the

series BiCo1

Fe o3

is that as the concentration of iron decreases, -x x

the sintered pellet becomes harder and more brittle.

24

Fi.gure 1

Latt~ce parameter (a) of Cub~c Phase

vs. Concentrat~on of co3+ (XC03+)

10.1850

10.1800

10.1750

I I

/

/

/

/

/

/

0 10 20 30 40 50 60 70 80 90 100

xco3+

Fi.gure 1

25

26

F:l.gure 2

B:iCo1

Fe o3 -x x

Amount of the Cubic (BCC) Phase

Formed as a Function of X(Co)

100

90

80

70 % Cubic

60

50

40

30

20

0~-----L------~----~----~~----~----~------~----~-------L----~ 0 10 20 30 40 50 60 70 80 90 100 Concentration of co3+ (in Bsite)

Figure 2

N -..J

28

The variation of lattice parruueter as a function of concentration

in the single phase BCC region does not seem to be unusual except

that for pure BiCoo3

the parar:teter a is much larger than for the

single phase solid solutions.

Preliminary magnetic measurements on BiCoo3

and BiAl0

_9

Fe0

_1

o3

• indicate that these coopounds are antiferromagnetic with N'eel tern-

0 peratures below 100 K, whereas BiCo

0_9

Fe0

_1

o3

exhibits a much more

complex magnetic behavior even at room temperature.

In view of our preliminary magnetic studies, the lattice para-

meters for BiCoo3 and BiAl0 • 9 Fe0 • 1 o 3 , a= 10.1928 i and 10.1870 i

respectively, exhibit the discrepancy expected on the basis of the

different ionic radii of Co+3 and Al+3 . For BiCo Fe 0 0.9 0.1 3'

BiCo0 • 5 Fe0 •5

o3 and BiCo0 _35

Fe0

_65o3

however, the magnetic measure-

ments indicate that there is some type of magnetic ordering even at

room temperature. The decrease in ~ in going from BiCoo3

to

BiCo 1 Fe o

3 seems to be the result of volume contraction caused

-x x

by magnetic ordering in the cell. Additional magnetic studies are

in progress and will be reported at a later date.

Previous investigators (Tomashpol'skii, Yu. Ya., et al., (1969)

have reported that BiCoo3

has a pyrochlore structure when synthesized

at atmospheric pressure, yet the compound of the same stoichiometry

synthesized in this laboratory could not be indexed on the basis of

such a structure. Although the powder pattern could be indexed on

the basis of a BCC structure, it was decided to grow single crystals

of BiCoo3

and BiCo1_x Fex o

3 in an attempt to unambiguously determine

the symmetry and to assign this class of isostructural compounds to a

possible space group.

29

F:lgure 3

Bi co. 9 Fe. 1 o3 Zero Level (Precession) Representation

of the Reciprocal Lattice in the

* * ( 0 b c Plane 1.9)

Blank Circles Represent Absent Olk Reflections

30

;'I' * c

0 0 0 0 1 2 3 4 l. l. l. l.

I'

II'

Ok4 Dk3 bk2 ... l<>k1

IIIII' b* • ' ~ .. 7 ...

1

~

Fi.gure 3

31

F1.gure 4

Bi Co • 9 Fe • 1 o3

Zero Level (Precession) Representation

of the Reciprocal Lattice (91.9°)

32

..... " c*

..

• b* " .. 7

Fi.gure 4

33

Fi.gure 5

B1. Co • 9 Fe • 1 o3 First Leve~ (Precession) Representation

of the Reciprocal. Latt:t.ce (1.9°)

34

/~a*

h h h h 1 2 3 4 1 1 1 1

4k1 3k1 2k1 k1 b* ..

' / .. ..

.. ..

Fi.gure 5

35

F:lgure 6

Bi. Co • 9 Fe • 1 0 3 First Level (Precessi.on) Representati.on

0 of the Reci.procal Latti.ce (91.9)

36

.If'.

* c

* ... b ' 7

..

I

Figure 6

37

Figure 7

B::l Co •5 Fe •5 o3

Zero Level {We::lssenberg) Representat::lon

of the Rec::lproca2 Latt::lce

38

.1'!' * a

~

...

.... II' b* ' /

Fi.gure 7

39

The single crystals subjected to X-ray analysis were

BiCo0 •9

Fe0 _1o3

and BiCo0 • 5Fe0

_5

o3

• On the basis of zero level

Weissenberg, and zero and first level precession photographs (Figures

3, 4, 5, 6 and?), the systems are seen to be cubic with h + k + 1 = 2n.

This condition restricts the systems to a body-centered lattice. In

addition Ihl~O ~ IkhO and this absence of a four-fold axis of symmetry

results in a Laue group, m3 (International Tables of Crystallography,

Vol. I). Absorption is of course a problem on the precession photo-

graphs (the crystal is approximately a trapezoid), yet it can also

be seen that a repeat pattern is not observed every ninety degrees

on the Weissenberg photograph.

Combination of the above conditions and restrictions yields

four possible space groups, I23

, I2 3

, Im3 and Ia3. The additional 1

condition on Okl, k(l) = 2n, eliminates Ia,3. Heasurements of p:iezo-

and pyroelectricity would be useful, for only Im3 is centrosymmetric.

Unfortunately we have been unable to grow sufficiently large crystals.

A comparison of the X-ray patterns to that of Er2o

3, which crystal­

lizes in the space group I2 3

, suggests that I2 3

might be eliminated. 1 1

A complete structural study employing Patterson and Fourier tech-

niques should unambiguously establish the space group and structure,

particularly with such a heavy atom as Bi.

Rough electrical resistivity measurements at liquid nitrogen

and room temperature on ~ellets of BiCoo3

and BiCo 1_xFexo3

:indicate

that they are semiconductors. (Table III).

CONCLUSIONS

A new class of isostructural AB03

compounds has been synthesized

B1.Co03

Bi.Coo. 9 Fe0.1 03

B1.Co0 • 5 Fe0.5 03

TABLE III

Resistivity of BiCo1

Fe o3 -x x

9 hm (RT) o -em

6.2 X 104

1 .6 X 1a3

5.9 X 104

3.1 X 105

3.2 X 105

2.5 X 105

40

41

and character~zed by X-ray methods. Preliminary magnet~c studies

indicate that these compounds possess unusual magnetic propert~es.

More detailed results wi11 be reported in the near future.

42

REFERENCES

BOKOV, V. A., HYL•NIKOVA, I. E., KIZHAEV, M. F., BRYZHINA, H. F., and GRIGORYAN, N. A., Soviet Physics-Solid State, z, 2993 (1965).

BUCCI, J.D., ROBERTSON, B. K. and JAMES, W. J., submitted to Acta-Cryst. (June 1971).

MOREAU, J. M., HICHEL, C. and JANES, W. J., Solid State Communications 7, 865 (1970).

• • NARAY-SZABO, I., Muegyetemi Kozlemenyek, l• 30 (1947).

NIIZEKI, N., Convention of the Physical Society of Japan, (1965).

SKINNER, S. H. , IEE Transactions, Pl,fP-6, 68, ( 1968) •

TOMASHPOL'SKII, Yu~ Ya. and VENEVTSEV, Yu. N., Inorg. Haterials, .,2, 7 (1969).

TO}~HPOL'SKII, Yu. Ya., ZUBOVA, E. V., BURDINA, K. P., and VENEVTSEV, Yu. N., Neorg. Hat., 2_, 2132 (1967).

TO}~HPOL'SKII, Yu. Ya., ZUBOVA, E. V., BURDINA, K. P., and VENEVTSEV, Yu. N., Soviet Physics-Cr~stallo~raphy, 12_, 859 (1969).

MAGNETIC .AND X-RAY STUDIES OF THE ISOSTRUCTURAL BiCo03 AND Bill •

9 Fe • 1 o

3 SYSTEHS

ABSTRACT

The magnetic properties of BiCoo3

and Bi.Al.9

Fe.1

o3

were

0 investigated in the temperature range 100-300 K. In this region

43

both materials are paramagnetic and !o~low the Curie-Weiss ~aw. The

0 0 Curie-Weiss constants are 1.044 K/mo~e and 0.23 K/mo~e for the

Co and Al-Fe compounds respective~y. The extrapo~ated e is -118°K N

0 for BiCoo

3, and -39 K for Bi A1.

9 Fe. 1 o

3• The thermal expansion

0 of BiCoo

3 was investigated in the temperature range 40-300 K. There

is a first order transition in the thermal expansion curve at 90°K •

• This transition is attributed to the anti!erromagnetic Nee~ temP-

erature.

INTRODUCTION

Recent~y a number of new Bi.M03

compounds were synthesized in

this ~aboratory. This artic~e reports some detai.~ed magnetic

studies on two of these compounds, namely BiCoo3

and BiA1.9

Fe. 1 o3

•

Because the M site is fu~~Y or partial~y occupied by a magnetic ion

(in all except BiAl03

) it wou~d seem reasonab~e to expect some

type of magnetic ordering in these materials. v

Bi.Coo3

has been previous~y reported by Tomashpo~'skii, Yu. Ya.,

and Venevtsev, Yu. N. (~969). They reported the magnetic studies on

Bico03

synthesized under ordinary conditions and the phase synthesized

under high pressure. To the former, they assigned the pyroch~ore

structure ~th a = 10.52 i, and to the latter the cubic perovski.te

44

structure with a = 4.228 2. They assert that the pyrochlore phase

is paramagnetic, while the high pressure phase 1s antiferromagnetic

The results reported by Temashpol'skii, Yu. Ya., Zubova, E. V.,

Burd1na, K. P., and Venevtsev, Yu. N. (1969) on the synthesis of

BiCoo3

and other BiM03

compounds did not resemble the results ob­

tained in this laboratory (first paper Of this series); therefore,

the results of the magnetic studies reported by Tomashpol'skii and

Venevtsev (1969) seemed worthy of fUrther investigation.

which is a rhombohedrally distorted perovskite is

0 antiferromagnetic with TK = 633 K. The

the body-centered cubic structure (BCC).

series BiA11

Fe o3

has -x x

The Fe3+ in BiA1.9

Fe.l o3

can then be looked upon as being a solution of magnetic ions in a

non-magnetic medium; although, the Al3+ ion does have empty 3d

orbitals available and could play a role in the Fe3+ - Fe3+ inter­

actions as the Fe3+ concentration increases. In the case of anti-

ferromagnetic ordering, superexchange interactions would undoubtedly

prevail in such a system.

EXPERIMENTAL

The magnetic measurements reported in this article were made

using the Gouy method. The balance utilized was a five-dec1m~

places Mettler H - 20 model. The magnet is a Varian electromagnet

with 3 in. pole faces.

The samples were cooled by using liquid nitrogen. Adjustment

of the evaporation rate of the liquid nitrogen permits the attain-

0 ment of temperatures in the range 100-270 K. This is accomplished

by directing the nitrogen vapors to the sample holder, which is

45

enclosed in in a double-wall glass dewar. The volume between the

two walls of the dewar can be evacuate~ thus preventing heat

losses, and condensation. For a more thorough r~v~ew, see Dickinson,

R. C. ( 1971).

The temperature is measured by a copper - constantan thermo-

couple. The reference for the thermocouple is a distilled water­

ice bath (= 0°C). The Gouy tube and gold chain used were calibrated

as a fUnction of temperature using the standard HgCo(SCN)4

whose

magnetic suscept~b~lity is given as:

6 -6 -1 xg = 1 .44 x 10 g 222._

10+T

The thermal expansion work was done ~th a back reflection

focusing camera. The camera and cr~ogenic setup are described by

Woodard, C. L. ( 1968) and Shah, J. S. (1971). The temperature control

+ 0 was better than _ 0.01 K. Cr Ka1

radiation was used throughout this

work. The high angle lines { &==- 70°) 831, 822, and 653 were used to

obtain the lattice parameters. The parameters reported are the

averages of the parameters obtained from all three lines. They are

not corrected for refraction or absorption.

RESULTS AND DISCUSSION

The investigation of the system BiA1.9

Fe. 1 o3

is of particular

interest from the standpoint of observing the behavior of a strong

magnetic ion (Fe3+) in a non-magnetic crystalline medium. ~gure 1

shows the behavior of the inverse of the molar susceptibility as a

function of temperature.

The behavior of BiA1.9

Fe.1

o3

is not unexpected. In the

0 range investigate~ 100-300 K, the susceptibility follows the Curie-

0 OK/ Weiss law rlth \ = -39 K, and C = 0.23 mole. Since ~ can be

46

F:i.gure 1

Bi Al • 9 Fe • 1 o3 Reciprocal Molar Susceptibility~ (mole- 1) vs.

0 Temperature T ( K)

1250

1 X:

-1 mol.e

1000

750

100

47

1.50 200 250 300

T (~)

Fi.gure 1

48

Figure 2

B:L Al. • g Fe. 1 o3 Magnet:Lzat:Lon (M) vs. Field (H)

10.0

8.0

M (Oe)

6.0

4.0

2.0

o.o 0 1000 2000

H (Gauss)

3000 4000 5000 Fi.gure 2

49

6000 7000

50

taken as a qualitative measure of the degree of antiferromagnetic

coup~ing, it is evident from the experimental value that the coupling

present is quite weak.

The magnetization curves are shown in figure 2. As can be

seen from the extrapo~ations of the magnetization (H) to H = 0, the

samp~e is free of any ferromagnetic impurities. The behavior is

• that of a typical antiferromagnetic material above the Neel temper-

ature. For the sake of c~arity the magnetization as a fUnction of

fie~d is reported only at four temperatures, including the lowest

and highest temperatures attained. The magnetization at other

temperatures fal~s between the upper and lower curves, and all

extrapo~ate to the same point at H = 0.

Some specu~ations can be made concerning the BiA11

Fe system -x x

over the entire range of x. If the Fe3+ ion is examined in terms of

the behavior of a strong magnetic ion in a non magnetic lattice

and, if the Fe3+ is ideally (randomly) distributed in such a lattice,

then it would be expected that as the concentration x is decreased

from 0.1 to 0 the antiferromagnetic (superexchange) interactions

should decrease and, eventually, the material should become para-

magnetic. The concentration at which BiAl1_x Fex o3 becomes para­

magnetic does not have to necessarily correspond to x = 0. If

the iron concentration is decreased below 0.1, there may be a point

where the Fe3+ - Fe3+ distance becomes large enough to prohibit

any superexchange interactions, thus leading to simple paramagnetic

behavior.

Conversely, as the concentration of iron is increased above

x = 0.1, the Fe3+- Fe3+ distance decreases until, at some specific

51

concentration, negat1ve Fe3+ - Fe3+ interactions can also appear

and give rise to a strong antiferromagnetic behavior. Of course,

th :tb~li.t f •t· F 3+ 3+ e poss ~ y o pos~ ~ve e - Fe interactions cannot be

completely ignored, in which case ferromagnetic behavior would

appear.

The magnetic properties of BiCoo3

previously reported by

Tomashpolts~i and Venevtsev (1969) ware for the ttpyrochlore struc-

ture" and for the high pressure cubic perovs~te phase. They reported

that the systems are paramagnetic and antiferromagnetic (TN< - 160°C)

respectively.

Since the B:l.Coo3

synthesized 1n this laboratory is a body­

centered cubic (first paper of this series), i.t was not unexpected

that the results of the present study did not agree with those

previously reported.

0 In the temperature range 100-300 K, BiCoo

3 obeys the Curie-

Weiss law. The experimental values or the constants eN and C are

-118 0 0

K, and 1.044 K/mole, respectively. These values are extracted

from figure 3, which shows the reciprocal molar susceptibility as a

fUnction of temperature. The magnetization curves for B:l.Coo3

are

presented in figure 4. As in the case of BiA1. 9 Fe. 1 o3

, only a

few curves are reported for the sake of clarity; however, all values

determined at other temperatures fall between the upper and lower

limit. They too extrapolate to the same point (M= 0) at H = o, as

' would be expected for a typical antiferromagnet above its Neal

temperature.

If the behavior of an antiferromagnet is examined in terms of

the two sublattice model, and applying the molecular field treatment

52

F:i.gure 3

B:1.Coo3

Reciprocal Molar Suscept:1.b:1.1:1.tyt (mole- 1)

vs. Temperature 'l(°K)

375

350

325

300

1 X: -1 mole

275

250

225

zoo

53

100 150 250

Fi.gure 3

54

Fi.gure 4

Bi.Coo3

Magnetization (M) vs. Fi.eld (H)

35

30

25

20

M Oe

15

10

5

0 1000

55

2000 3000 4000 5000 6000 7000

H (Gauss)

F:1gure 4

56

(Dekker, A. J., 1952, ~ttel, c., 1967). at temperatures above T, the N

follo~ng equat~ons result:

eN c

({3 + a) ( 1) = 2 and

TN c

( f3 - a) (2) =-z where

c N ~i g2 J (J+l) = 3k

and a and f3 are pos~t~ve We~ss molecular f~eld constants.

If a, wh~ch represents the pos~t~ve A - A ~nteract~on, ~s

small then TN ~ eN. Of course the value of theta ~s understood

to be negat~ve. If t~s were true ~n BiCoo3

, then the expected

• Neal temperature trans~t~on should be in the v~c~nity of 120°K. As

the A - A ant~parallel ~nteractions become :Lmportant, ex ~ncreases

and it becomes evident from equation (2) that TN decreases from

the expected value of TN """' eN.

In the magnet~c stud~es of BiCoo3

, no transition was observed

0 in the temperature range from 100 to 300 K, the l~mit of our

apparatus. For this reason ~t was dec~ded to extend the study by

conduct~ng thermal expansion exper~ments.

Magnetic trans~t~ons are generally of the f~rst order type;

therefore, prec~se thermal expansion ~nvestigations using X-ray

methods generally reveal the presence of such transitions.

A problem which cannot be ~gnored in magnetic studies is that

of contamination of the bulk sample by small amounts of magnetic

~mpur~ties. If the magnetic impurities cause a particular type

of behavior to be observed in magnetic studies of the bulk sample,

the behavior of the sample in question cannot be separated from

that of the 1mpurity. In the thermal expansion of a crystallo-

57

graphic lattice however, the impurity does not make a significant

contribution; therefore, any transitions which appear in the lattice

expansion curve can be safely attributed to the material in question.

The problem then becomes one of logical and adequate interpretation

of such transitions.

The thermal expansion of BiCoo3

was studied in the range

0 40-300 K. The results are plotted in figure 5. The break in the

0 curve at 90 K is attributed to the antiferromagnetic transition.

From the foregoing discussion, it was initially anticipated

0 that TN for BiCoo

3 should be about 120 K, assuming that the A- A

antiparallel interactions were negligible. It is obvious that

although such interactions are not very pronounced in BiCoo3 , they

cannot be neglected entirely if the magnetic behavior is to be

explained on a quantitative basis.

CONCLUSIONS

The isostructural compound BiA1. 9 Fe. 1 o3 and BiCoo3 are

both antiferromagnetic at low temperatures. Although the inter-

actions responsible for the antiferromagnetic behavior appear to

be predominatly of the superexchange type, more detailed neutron

diffraction studies are needed to more adequately explain the

nature of the observed antiferromagnetic behavior.

F:i.gure 5

B:1Co03

Latt~ce Parameter a vs. Temperature T (°K)

59

10.1850

10.18oO

10.1750

10.1700

10.16.50

10.1600

0 350 Fi.gure 5

REFERENCES

DEKKER, A. J. Solid State Physics, Mc~allan & Co. Ltd., London (1952), pp. 484-488.

DICKINSON, R. c., Ph. D. Dissertation, University of Missouri­Rolla (1971).

KITTEL, c., Introduction to Solid State Physics, John Wiley & Sons, Inc., New York (1967), pp. 472-487.

Go

TOMASHPOL 1 SKII, Yu. Ya. and VENEVTSEV, YU. N., Inorg. Materials, ~ 7 (1969).

TOMASHPOL'SKII, Yu. Ya., ZUBOVA, E. V., BURDINA, K. P., and VENEVTSEV, Yu. N., Soviet Physics-Crysta1lography, 13, 859 (1969).

SHAH, J. s., Ph. D. Dissertation, University of Missouri-Rolla (1971)

WOODARD, c. L., Ph. D.,~ssertation, University of Missouri-Rolla (1968).

61

}'lAGNETIC TRANSITIONS IN BiCo Fe 0 • 9 • 1 3

ABSTRACT

The magnetic behav~or of BiCo.9

Fe. 1o3

was investigated in the

temperature range from 100 to 300°K. The results are interpreted

as arising from the localization of moments on both kinds of mag-

netic ions present in the compound. An anomaly appears in the mag­

netization curves at 125°K which may arise from a transition from

a ferromagnetic to a noncolinear ferromagnetic phase. From 125 to

0 165 K a time-dependence is observed for the molar susceptibility

of BiCo.9Fe.

1o3

as a fUnction of applied field strength. It is

postulated that in this range the noncolinear structure is disappear-

0 ing and that above 165 K the localized ferromagnetic phase is be-

coming less and less ordered. The lattice parameter of cubic

BiCo Fe 1o3

was precisely measured in the region 40-750°K. The • 9 •

thermal expansion data appear to support the anomalies observed

in the magnetic studies, i.e., there is a break in the lattice

expansion curve at 125°K and a change in slope at approximately

300°K. The latter anomaly ia attributed to the ferromagnetic

Curie temperature.

INTRODUCTION

The synthesis of a new class of isostructural BU-103

cubic

compounds was reported in the first paper of this series. Some

of the compounds reported were those of the solid solution series,

BiCo1

Fe o3

• In the investigation of the magnetic properties -x x

62

of bismuth cobaltite (second paper of this series), BiCoo3

was

' found to be antifarromagnatic with a Neel

Bismuth ferrite is also antiferromagnatic

temperature, TN' of 95°K.

0 with TN = 623 K (Moreau,

Michal and James, 1970, Bucci, Robertson, and James, 1971). The

structure of BiFeo3 is rhombohedral while that of BiCoo3

is cubic.

The synthesis of the series BiCo1

Fe o3

reveals that co3+ cannot -x x

3+ be substituted for Fe in the iron-rich side (paper I of this series).

It would not be surprising, therefore, if ferric ions do not retain

their antifarromagnetic ordering upon substitution into the BCC

bismuth cobaJ.t:1.te. lattice.

The synthesis of materials from oxides containing a magnetic

ion presen~a great problem to subsequent magnetic studies. The

usual chemical and physical methods employed are rarely sufficiently

sensitive to detect the minute quantities of magnetic impurit~es which

can invalidate such studies, and for this reason susceptibility mea-

surements alone cannot be taken as conclusive evidence for bu~

magnetic behavior. To substantiate the temperature dependence of

various magnetic parameters it is common practice to determine the

expansion of the lattice parameter, a bulk property which is un-

affected by trace amounts of impurities. Such measurements sometimes

enable one to decide whether magnetic transitions are in fact a

property of the bulk sample or merely the result of unknown magnetic

impurities present in the sample.

One of our solid solutions, BiCo.9

Fe. 1 o3 , exhibited unusual

magnetic properties, and for the above reason we investigated the

lattice expansion as a function of temperature.

63

EXPERIMENTAL

With one exception the experimental procedures and equipment

used in this study are identical to those in the second paper of

this series. The solid solution, BiCo.9

Fe.1

o3

, is strongly mag­

netic at room temperature. At 125°K this effect is so large (even

at~ 200 Gauss) that a pure sample is pulled into one of the magnetic

faces. For this reason the sample was diluted With confectioner's

sugar. The solution, 45.697% by weight BiCo.9

Fe. 1 o3

, was thoroughly

mixed for one hour to insure homogeneity of the sample. The appro-

priate diamagnetic corrections for the sugar were made and found to

be small (a fraction of one percent).

The high temperature X-ray data were collected on a Seemann

114 mm camera using Cr Ka1 ( "A= 2.28962 i) radiation. The experi­

mental details are described by Bucci, et. al. The high angle

reflections 653 a,. 822 a1 and 831 a1 were used to calculate the

lattice parameter, ~·

RESULTS AND DISCUSSION

In this laboratory the usual method for determining magnetic

susceptibilities as a function of temperature is to make a series

of measurements at different field strengths and room temperature

(the upper temperature limit of our apparatus), then to drop immedi­

ately to 100°K (the lower temperature limit). The susceptibility

is measured as a fUnction of temperature as the temperature is raised.

This method is satisfactory for parruaagnetic and antiferromagnetic

materials, but for ferro- and ferrimagnetic materials a thermal

hysteresis may exist, i.e., different susceptibility (or magnetization)

cur~es dependent upon the direction of the temperature change.

64

The diluted sample was packed in a Gouy tube and the suscepti­

bility measured at room temperature and at 100°K. Equilibration in

the magnet was immediate. As the temperature was elevated, however,

a new phenomenon was observed. In the range frau 124 to 165°K, a

time dependence of the susceptibility was noticed. Althcugh it is

true that eddy-current forces can arise when a magnet is switched on,

it is significant that we observe this strong time dependence only in a

certain range, namely, from 124 to 165°K. At 124°K, where this

effect is most pronounced, it may take as long as thirty-five min­

utes for the weight to stabilize. Below 124°K and above 165°K the

effect disappears. The temperature was found to be the same at

both the beginning and conclusion of each run.

The data reported in this paper were obtained on a vir gin sample.

To determine the presence of a thermal hysteresis, measurements were

0 made on the sample from room temperature down to 112 K and back up

to room temperature. At each temperature the susceptibility was

measured as a function of field strength to determine the presence

of magnetic hysteresis.

The magnetic hystereses curves at different temperatures are

shown in Figures 1-8. The actual parameter plotted is the magnetiz-

ation, :H, g:l.ven in our case by

M- X H - M applied.

These figures correspond to a continual decrease from room temP-

erature to 112°K. Two values of Mare plotted, one a value extra-

polated to t = 0, the other an equilibrium value specified as t = = .

In this run the time dependence is first observed at 162.24°K.

Although negative fields could not be generated with our equipment it

65

F:Lgure 1

M(Oe) vs. H(Gauss)

0 T = 112.0 K

o = Decreasing F:Le~d

• = Increasing Field

66

T = 112.0 °K

175

150

0~

125

100

1 3 4 5 6 7 H (Gauss)

Figure 1

67

F:igu.re 2

M(Oe) vs. H (Gauss)

0 T = 124.21 K

o = Decreasing Field

• = H at ti.me t = oo

Increasing Fi.eld

0 = M at time t = 0

1.50

125

M Oe

100

75

68

50 ~-------L--------L--------L--------~------~--------L-------~~ 2000 3000 4000 5000 6000 7000 1000

H (Gauss) figure 2

69

F:i.gure 3

M(Oe) vs. H (Gauss)

0 T = 13?.03 K

o = Decreas~ng F:i.eld

• = M at t~me t = oo

Increasing Field

0 = 11 at time t = 0

150

12.5

M Oe

100

75

50

0 1000 2000

70

3000 4000 5000 6000 7000

H (Gauss) Fi.gure 3

71

Fi.gure 4

M(Oe) vs. H (Gauss)

0 T=149.1K

o = Decreas~ng Field

• = M at t~me t = oo Increasing Field

<) = H at t~me t = 0

150

125

M Oe

100

75

72

50~------~------~------_.------~--------L-------~------~~ 0 1000 2000 3000 4000

H (Gauss)

5000 6000

Fi.gure 4

7000

73

Figure 5

H(Oe) vs. H (Gauss)

0 T = 162.24 K

o = Decreas~ng Fie~d • = H at t:1me t = oo

Increas~ng Fi.e~d

<:> = M at time t = 0

150

125

M Oe

100

75

74

50L_ ______ -L------~~-----=~=-----~~----~~~----~~~--~~~ 0 1 000 2000 3000 4000

H (Gauss)

Fi.gure 5

75

F:igure 6

M(Oe) vs. H (Gauss)

0 T = 183.75 K

o = Decreasing Field

• = Increasing Field

150

125

M Oe

100

75

H (Gauss)

Figure 6

76

77

Fi.gure 7

M(Oe) vs. H (Gauss)

0 T = 205.56 K

o = Decreas~ng Field

• = Increasing Field

150

125

}.1

Oe

100

75

0 T = 205.56 K

78

50~----~~~--~~=-----~~----~~~---=~~--~~=---~~~ 0 1000 2000 3000 4000 5000 000 7000

H (Gauss)

Fi.gure 7

79

Fi.gure 8

M(Oe) vs. H (Gauss)

0 T = 239.0 K

o = Decreas~ng Field

• = Increasing Field

150

125

M Oe

100

75

50 0

0 T = 239.0 K

1000 2000 3000 4000

H (Gauss)

F:lgure 8

5000

80

000 7000

81

is apparent from the graphs that as the temperature is decreased from

239°K to 124°K the hysteresis tends more and more towards a square

loop, the technologically desired property. At 112°K (Figure 8)

the hysteresis has essentially disappeared, indicating a sharp

transition between 124°K and 112°K.

The thermal hysteresis curves at different fields strengths

are shown in Figures 9-11 1 and the lattice expansion curve is plotted

as Figure 12. The spontaneous magnetization curve is represented by

Figure 13. The values for the spontaneous magnetization, M , are 0

extracted from the magnetization curves (Figures 1-8) by extrapol-

ating the upper curve to H = 0.

Two models can be postulated to explain the unusual magnetic

behavior of BiCo.9

Fe.1o

3• Both BiFe0

3 and BiCoo

3 are antiferromagnetic,

and this fact suggests that the solid solution behaves in much the

s~ew~. One model might employ the random substitution of Fe3+ for

co3 + in the Bieoo3

lattice, the result being an uncompensated anti­

ferromagnetic structure. The incomplete compensation leads to a very

weak ferrimagnet, for the moments of the two ions are not equivalent.

The solid solution BiCo.9

Fe. 1o

3 would be uncompensated by approximately

0.02 Bohr magnetons; BiCo Fe 5

o3

by approximately 0.25 Bohr magnetons. • 5 .

Such a model is difficult to accept for two reasons. Firstly, the

s~ple adheres to the magnet pole faces at fields as low as 200 Gauss,

which indicates much larger degrees of non-compensation; and, secondly,

in this model there is no reason for the hysteresis to vanish below

A second model seems more reasonable. Let the Fe3 + undergo pre-

ferred substitution and produce localization of moments on both kinds

82

F:i.gure 9

0 M(Oe) vs. T( K)

H = 3000 Gauss

o = Decrease ~n T

• = Increase in T

82

Figure 9

M(Oe) vs. T(°K)

H = 3000 Gauss

0 = Decrease in T

• = Increase in T

84

Fi.gure 10

M(Oe) vs. T(°K)

H = 4000 Gauss

0 = Decrease in T

• = Increase in T

150

125

M(Oe)

100

75

H = 4000 Gauss

250 Fi.gure 10

85

300

86

Figure 11

M(Oe) vs. T(°K)

H = 7000 Gauss

0 = Decrease in T

• = Increase in T

175

150

M(Oe)

125

100 100 200

H = ?000 Gauss

250 F:l.gure 11

8?

300

88

Figure 12

0 Latt~ce Parameter a vs. T( K)

89

10.2100

10.2000

10.1900

a (i.)

10.18oO

10.1700

10.1600

10.1500

J".l.gure 12

90

Fi.gure 13

0 Spontaneous Magnet~zat~on Mo vs. T( K)

100

90

80

70

60 Mo(Oe)

50

40

30

20

10

0

'

100 T a 150 Tb 200 250

T(°K)

300

' ' '

Figure 13

' ' ' 350 T

c

\0

400 ...

92

of magnetic ions. This view is supported by previous investigators

working with interu1etallic compounds (Lemaire, 1971; Moreau, Michel,

Simmons, O'Keefe, and James, 1971; Givord, Lemaire, James Moreau, and

Shah, 1971), who showed that the electronic behavior of cobalt and iron

are quite ~fferent. The d orbitals of iron tend to be localized

whereas coba1t appears to be dependent on the nature of other sub-

stituents present in the compound.

This difference in behavior ia not completely unexpected if

Fe3 + (3d5 ) and co3 + (3d

6) are viewed in terms of their electronic

configurations. Any type of magnetic interaction, be it superexchange,

double exchange, or of the A-A type, should require a degree of delocal-

ization of electrons either out of or into the 3d orbitals. The iron

6 ion, whose term symbol is S, has an extremely stable half-filled 3d

shell with a high magnetic moment. Such an ion would be reluctant to

allow delocalization of its 3d electrons.

On the other hand, the cobalt ion, ~th term symbol 5n, has six

3d electrons and should be more amenable to delocalization. Dependent

upon the nature of other substituents, the sixth electron could either

be delocalized to produce the stable 3d5 configuration or accept

6+n delocalized electrons to yield a 3d configuration. This may explain

why the only bismuth-containing perovskite with rhombohedral distortion

formed under ordinary conditions is BiFeo3

•

On the basis of a localized moment medel, B1Co.9

Fe. 1o3

can be

0

considered to be paramagnetic above 380 K. As the temperature is de-

creased from 380 to 170°K, both magnetic and thermal effects are oper-

ative and the structure becomes more ordered. The time dependence of

0 susceptibility sets in at 165 K, interpreted as a predominance of

93

magnetic effects. The time dependence becomes greater and the mag-

netic hysteresis increases markedly down to 124°K. At 112°K the

hysteresis vanishes almost entirely (Figures 1-8).

The behavior from 165-124°K is interpreted in the following

manner. Fe3+ interactions, probably of the superexchange

type, are positive. The localization of the moment on Fe3+ tends

to pertrub near-neighbor cobalt ions, and as the temperature is

0 decreased from 165 to 124 K the preturbation increases. The cobalt

ion favors negative interactions in BiCoo3

(second paper of this

series), therefore if it is to couple antiferromagnetically it must

first overcome the Fe3+ perturbation. One way to accomplish this is

to decrease the volume of the lattice suddenly (Figure 13) to attain

the distances required for negative interactions where coupling can

0 occur. Thus from 165 to 124 K it is possible that a noncolinear

magnetic structure exists. 0

Below 124 K an uncompensated antiferro-

magnet appears which is in effect a very weak ferrimagnet. Such a

ferrimagnet would not exhibit a large hysteresis.

The second model can explain the spontaneous magnetization and

thermal hysteresis curves, but additional magnetic data must be

collected above and below the investieated range before final con-

elusions can be drawn.

94

CONCLUSION

The magnetic properties of BiCo.9

Fe.1

o3

were investigated.

The conclusions that are drawn are of course speculative.

Further work is required on the subject in order to better

understand the magnetic and electrical properties of the series

BiCo1

Fe o3

• -x x

REFERENCES

BUCCI, J. D., RCBERTSON, B. K. and JAMES, W. J., submitted to

Acta-Cryst. (June 1971).

95

GIVORD, D., LEMAIRE, R., JAJ1ES, W. J., MOREAU, J. 1'-1., and SHAH,

J. s., Intermag Conference, Apr~l 1971

LEMAIRE, R., Pr~vate commun~cat~ons (1971).

MICHEL, C., MOREAU, J. H., ACHENBACH, G. D., GERSON, R., and

JAMES, W. J., Sol~d State Commun~cat~ons, 1• 701 (1969).

MOREAU, J. M., MICHEL, C., SIHHONS, H., 0 1 KEEFE, T. J., and

JAMES, W. J., Journal de Physique,£!, 670, (1971).

96

VITA

Joseph Donato Bucc~ was born ~n Spinete Prov. Campobasso, Italy,

on August 8, 1944. He obtained the B. s. degree in Chemistry from

Manhattan Collage, New York, N.Y.

The author has been enrolled ~n the Graduate School of the

University of ~ssour~-Rolla s~nce September 1967. During the academ~c

year 1967-68 the author was a teac~ng ass~stant ~n Chemistry.

Subsequently he was awarded an NDEA fellowah~p in Che~stry for

the period 1968-71. Dur~ng the same per~od the author held a part­

t~me teac~ng assistantship.

97

APPENDIX A

LATTICE PARAHETERS OF Bi.Fe03

AS A FUNCTION OF T(°C)

T(°C) ~· c ... h

25.14 5.57793 13.8670

32.12 5. 57851 13.8695

45.37 5-57937 13.8718

58.70 5.57949 13.8742

180 5.5815 13.876

2.35 5.5857 13.893

313 5.5914 13.929

344 5.5945 13.92.3

398 5-5973 13.934

398 5.5981 13.936

441 5.6017 13.944

495 5.6073 13.964

495 5.6071 13.961

597 5.6151 13.974

675 5.6170 13.979

704 5.6198 13.979

725 5.6215 13.984

756 5.6230 13.989

797 5.6256 13.980

819 5.6277 13.982

838 5.6278 13.984

* not corrected £or refraction

98

APPENDIX B

LATTICE P ARM'lETERS OF Bi.Coo3

AS A FUNCTION OF T(°K)

T(°K) a*db

40 10.1585

65 10.1612

80 10.1624

85 10.1626

90 10. 1639

95 10. 1636

100 10.1629

110 1 o. 1658

140 10.1689

180 10.1737

295 10.1871

* not corrected for refracti.on

99

APPENDIX C

LATTICE PAR~~ERS OF BiCo.9

Fe_ 1o3

AS A FUNCTION OF T(°K)

T(°K) a*(~)

40 10.1498

60 10.1523

80 10. 1546

100 10. 1561

110 10.1588

120 10.1575

130 10.1584

140 1 o. 1593

160 10. 1626

180 10.1654

295 10.1779

345 10.1816

365 1 o. 1822

378 1 o. 1829

513 10. 1900

546 10. 1920

723 10.2161

• not corrected for refraction