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Chapter : 5
Growth and characterization of BaxCd1-x(IO3)4 crystals
Publications :
“Growth and characterization of gel grown crystals of
BaxCd1-x(IO3)4”
S.L. GARUD and K.B. SARAF
Bulletin of Material Science, [Communicated]
115
Chapter : 5
Growth and characterization of BaxCd1-x(IO3)4 crystals
5.1 Introduction …………………………………………….. 1165.2 Crystal growth ………………………………………….. 117
5.2.1 Chemicals ………………………………………... 1175.2.2 Experimental details …………………………….. 1175.2.3 Nucleation ……………………………………….. 118
5.3 Results and discussion ………………………………….. 1185.4 Observations ……………………………………………. 1205.5 Effect of various parameters on crystal growth ………… 122
5.5.1 Effect of gel density ……………………………… 1225.5.2 Effect of pH of gel ……………………………….. 1255.5.3 Effect of gel aging ……………………………….. 1275.5.4 Effect of concentration of reactants ……………… 1295.5.5 Concentration programming …………………….. 130
5.6 Characterization ………………………………………… 1315.6.1 X-ray diffraction …………………………………. 1315.6.2 Fourier transform infrared (FT-IR)
spectral analysis ………………………………….. 1335.6.3 Scanning electron microscopy (SEM) …………… 1355.6.4 Energy dispersive analysis (EDAX) ……………... 1375.6.5 Thermal analysis …………………………………. 137
5.7 Conclusions …………………………………………….. 141References …………………………………………………… 143
116
Chapter : 5
Growth and characterization of BaxCd1-x(IO3)4 crystals
5.1 Introduction
The growth of crystals in gels was recorded in 1913 when
Liesegang, Bradferd, and Holmes studied the formation of ‘Liesegang
rings’ [1-3]. Afterwards, mechanism of growth has been discussed
extensively by many co-workers [4-8]. Their work accelerated the
mechanism of growth and characterization of crystals in gels.
Gel growth in aqueous solution is now a wide spread technique
for production of high quality crystals in a large range of solubilities
and temperature [9-11]. In gel growth, crystals are mostly formed at
ambient temperature and hence are free from strain often present in
crystals prepared from the melt or from the vapour [12]. In this
method, two soluble reactants are diffused into a gel where they react
to form an insoluble product. In this method, large scale movements
like convection currents are almost completely suppressed, which
otherwise could be harmful to the quality of crystal. The presence of
gel does not affect considerably the rate of diffusion of crystallizing
species [13] and the related crystal growth kinetics. The principle role
of gel appears to be the suppression of turbulence and nucleation, [14]
due to which crystallization occurs by diffusion of reactants to a small
number of nucleation centers.
In recent years, very few attempts have been made to study
growth and characterization of iodate crystals in general and cadmium
iodate crystal in particular. Only a single attempt is made to study
cadmium iodate crystals [15]. The growth of cadmium iodate crystals
by gel technique by single and double diffusion method is reported.
117
However, there are no reports in the literature on the growth of mixed
iodate crystals by gel method. In the present work, growth of mixed
iodates i.e. barium-cadmium iodate crystals are described and
discussed. Out of number of parameters, density of gel, gel aging, pH
of gel, concentration of reactants are important factors which
considerably affect the growth of crystals. Optimum growth conditions
were determined and are reported.
5.2 Crystal growth
The growth of barium cadmium iodate crystals was carried out
by single diffusion techniques. Apparatus used for carrying out these
experiments were, borosil glass test tubes of 25 cm in height and 2.5
cm in diameter, a magnetic stirrer, digital pH meter (Systronics, Model
No.315), burettes and pipettes, beakers, etc.
5.2.1 Chemicals
Commercial grade sodium meta silicate (Na2SiO3)
Acetic acid, AR grade, Loba Chemicals (CH3COOH)
Barium chloride, AR grade, Loba Chemicals (BaCl2)
Cadmium chloride, AR grade, Loba Chemicals (CdCl2)
Sodium iodate, AR grade, Loba Chemicals (NaIO3)
Potassium iodate, AR grade, Loba Chemicals (KIO3)
5.2.2 Experimental details
Various concentrations of acetic acid and those of sodium
metasilicate were used to prepare gel. For this purpose, 5 cc, 2 N acetic
acid was taken in a beaker, to which sodium metasilicate solution
having different densities was added drop by drop with constant
stirring by using magnetic stirrer. It avoids premature local gelling. To
118
this mixture, 5 cc solution of barium chloride and cadmium chloride
was added with constant stirring. The pH of the mixture was
maintained at 4.4. Experiments were performed to optimize suitable
pH value for growth of good quality crystals. This mixture was then
transferred to the test tube and it was closed with cotton plug. The gel
was allowed to set. It took nearly 10 days for setting. This set gel was
aged for 4 days. Aging helps in nucleation control due to reduction in
the diameter of the capillaries in gel. Potassium or sodium iodate was
used as supernatant. Supernatants having different molarities were
carefully poured over the set gels.
The chemical reaction inside the gel can be expressed as
xBaCl2 + (1-x)CdCl2 + 4YIO3 = BaxCd(1-x)(IO3)4 + 4YCl,
where Y=K or Na
5.2.3 Nucleation
Nucleation takes place after 8 to 10 days. Numbers of nuclei
were observed near the gel interface. Number of nuclei is inversely
proportional to the distance from the gel interface. As the distance
from the gel interface increases, number of nuclei decreases.
Formation of nuclei depends upon number of parameters such as
density of gel, aging, pH, concentration of reactants, etc.
5.3 Results and discussion
The optimum conditions for the growth of barium cadmium
iodate crystals are reported in Table 5.1. Parameters such as gel
density, gel setting time, gel aging time, concentration of reactants, pH
of gel have considerable effect on growth of crystals.
119
Table 5.1: Optimum conditions for growth of barium-cadmium iodatecrystals.
Parameters Optimum condition
Density of sodium meta silicate solution 1.04 g/cm3
Amount of 2N acetic acid 5 ml
pH of mixer 4.4
Temperature Room temp.
Concentration of NaIO3 or KIO3 0.4 M
Concentration of BaCl2 or Ba(NO3)2 0.05 M
Concentration of CdCl2 or Cd(NO3)2 0.5 M
Gel setting time 10 days
Gel aging time 96 h
Period of growth 3 weeks
Crystals having different morphologies were obtained.
Prismatic crystals of size 2 mm x 2 mm x 1 mm far away from gel
interface and prismatic pyramidal crystals of size 2 mm x 2 mm x 2
mm away from gel interface were obtained. It was observed that the
number of crystals growing diminished with the increase in the
distance from gel interface. It may be due to reduced rate of diffusion
of supernatant. Second reason may be attributed to the aging of gel,
since crystals in this region nucleate in a comparatively older gel.
Increase in aging of gel reduces number of nucleation centers
and growth rate. Insufficient gel aging often leads to the fracturing of
gel at the time of addition of supernatant.
120
5.4 Observations
Figure 5.1 shows dendritic growth of barium cadmium iodate
crystals inside the test tube for high concentration of reactants.
Figure 5.2 shows prismatic transparent crystals of barium cadmium
iodate inside the test tube. Figure 5.3 shows few prismatic transparent
crystals of barium cadmium iodate. At one end, crystals are translucent
which is due to the inclusion of silica gel.
Fig. 5.1: Dendritic growth of barium- cadmium iodate crystals
121
Fig. 5.2: Prismatic transparent crystals of barium cadmium iodateinside test tube
Fig. 5.3: Few prismatic transparent crystals of barium cadmium iodate.
122
5.5 Effect of various parameters on crystal growth
It is necessary to study the effect of various parameters crystal
growth rate. Growth mainly depends on gel cell size, and cell size is
influenced by gel density, gel age, pH of gel, etc. Hence, these
parameters have profound influence on nucleation density, growth rate,
habit, and quality of crystals [16-18]. Concentration of reactants and
concentration programming has major impact on size, morphology and
habit of crystals. Hence, effect of all these parameters on growth of
crystals is discussed in the following sections.
5.5.1 Effect of gel density
The proper range of specific gravity of growing good quality
single crystals is 1.03 to 1.07, according to Henisch [19]. The gels of
different densities were obtained by mixing sodium meta silicate
solutions of specific gravity 1.03 to .06 with 2N acetic acid, keeping
pH value constant. As density decreases, transparency of the gel
increases. As a rule, very dense gels produce poor crystals. On the
other hand, gels of insufficient density take long time to form and are
mechanically unstable.
Table 5.2 shows the effect of gel densities on the quality of
crystals. Fig. 5.4 shows the variation of time of gelation with gel
density.
123
Table 5.2 : Effect of gel density on setting time
(pH = 4.4, Feed solution 0.05 M BaCl2 and 0.5 M CdCl2)
TestTubeNo.
Aceticacid2N(cc)
KIO3
incorporatedin gel 0.5M(cc)
Densityof gel(gm/cc)
Gelsettingtime(days)
Observations
1 5 5 1.02 15 Gel is unstable
2 5 5 1.03 13Takes very longtime to set, still nosufficient firmness.
3 5 5 1.04 10Few prismatic,prismatic pyramidalcrystals
4 5 5 1.05 8Number of crystalsdecrease, Prismatic,pyramidal crystals.
5 5 5 1.06 5Less transparent,few crystals.
6 5 5 1.07 2Opaque few crystalsand not well defined.
02468
10121416
1.02 1.03 1.04 1.05 1.06 1.07
Gel density (gm/cm2)
Gel
set
ting
time
(day
s)
Fig. 5.4 : Variation of gel setting time with gel density
Table 5.3 shows the effect of density on number of nuclei
formed. Fig. 5.5 shows the graph of gel density versus nucleation
density. Sodium meta silicate solution of specific gravity 1.04 gm/cc
and acetic acid (2N) with 4:1 ratio is an ideal combination for gel
formation in the present case. It is observed that the nucleation density
decreases as gel density increases.
124
Table 5.3 : Effect of gel density on number of nucleation
(pH = 4.4, Feed solution 0.05 M BaCl2 and 0.5 M CdCl2)
TestTubeNo.
Aceticacid2N(cc)
KIO3
incorporatedin gel 0.5 M(cc)
Densityof gel(gm/cc)
Numberof nucleiformed
Observations
1 5 5 1.02 35Small opaquecrystals, more innumber.
2 5 5 1.03 28
Number ofcrystals less,bigger in size,transluscent
3 5 5 1.04 15
Good, prism,pyramidal, fewtransluscent, fewtransparentcrystals.
4 5 5 1.05 12
Small, prism,pyramidal,transluscentcrystals.
5 5 5 1.06 7
Low nucleationdensity, small,transluscentcrystals.
6 5 5 1.07 5Crystals are few,opaque and notwell defined.
125
05
10152025303540
1.02 1.03 1.04 1.05 1.06 1.07Gel density (gm/cm2)
Num
ber o
f nuc
leat
ion
Fig. 5.5 : Variation of number of nucleation with gel density
5.5.2 Effect of pH of gel
It is generally known that initial pH value of the gel does not
indicate the acidity of the gel after gelation. Even then, these pH values
will have a profound effect on the gel structure, nucleation and growth
of the crystal as observed during the present investigation. The pH of
the gel was varied by changing the composition of acetic acid and
sodium metasilicate. Table 5.4 shows the effect of different pH values
on gel settling time and the quality of crystals obtained. The optimum
value of gel pH to get ideal gel is found to be 4.4. At pH values less
than 4.4, the time for gelation increased and the resultant gel was
unstable, and for pH values greater than 4.4, the gelation occurred very
soon and the resultant gel was not transparent. Fig.5.6 shows the graph
of pH against setting time in hours. In the present work, pH value of
4.4 is the optimum condition to grow good quality crystals.
126
Table 5.4 : Effect of pH on gel
(Aging period = 96 hours, Feed solution 0.05 M BaCl2 and 0.5 M
CdCl2)
TestTubeNo
Aceticacid2N(cc)
KIO3
incor-poratedin gel0.5 M(cc)
Solutionmeta-silicate1.04gm/cc
pH ofmixture
Gel settingperiod(hrs)
Observations
1 5 5 17.5 2.0 - gel is not set
2 5 5 17.8 2.5 - gel is not set
3 5 5 18.2 3.0 -gel still loose after30 days
4 5 5 18.6 3.5 300 platy, transluscent
5 5 5 19.0 4.0 240
good, transluscent,small sizetransparent,crystals
6 5 5 19.2 4.4 220
more nucleationdensity, good, fewtransluscent, fewtransparent, andwell developedcrystals
7 5 5 19.5 4.5 180transluscent, fewwell developedcrystals
8 5 5 20.1 5.0 152numbers ofcrystals decrease,transluscent
9 5 5 20.6 5.5 96prism shaped,opaque crystals.
10 5 5 21.1 6.0 40small opaquecrystals.
11 5 5 21.6 6.5 7dendrites areobtained
12 5 5 22.5 7.0Immediate
settingdendrites, opaque,not well defined.
127
0
50
100
150
200
250
300
3 3.5 4 4.5 5 5.5 6 6.5 7 7.5pH
Gel
set
ting
time
(hou
rs)
Fig. 5.6 : Variation in gel setting time with pH
5.5.3 Effect of gel aging
To study the effect of aging on gels, gels of same pH and density
were allowed to age for various periods. Supernatant of constant
molarity was then added as a feed solution over the gel. It was found
that the number of barium cadmium iodate crystals decreases as the
aging of gel increases. Aging of gel decreases the diffusion and
nucleation density. More aging causes more amount of water
evaporation out of the gel. The effect of water evaporation should be
considered before and after the formation of gel framework. Before
the gel is set, the evaporation of water causes an increase in gel density
which in turn decreases the diffusivity of reactive ions in the gel,
thereby decreasing the number of nucleation sites. After the gel is set,
the evaporation of water causes not only the lack of ionic carriers in the
channel of gel framework, but also discontinuities in the channel due to
the shrinkage of gel. Both these effects would adversely affect the
diffusion of reactants ions hence the observed decrease in the number
of nucleation sites. Table 5.5 shows the effect of aging time on number
and the quality of crystals. Fig. 5.7 shows graph of aging in hours
versus number of crystals. In the present work, aging of 96 hours was
found most suitable.
128
Table 5.5 : Effect of gel aging time
( pH = 4.4, Feed solution 0.05 M BaCl2 and 0.5 M CdCl2)
TestTubeNo
Aceticacid2N(cc)
KIO3
incorpo-rated in gel0.5 M (cc)
Solution ofmetasilicate(1.04gm/cc)
Agingtime(hours)
Numberofcrystals
Observations
1 5 5 19 24 35High nucleation,dendritic growth
2 5 5 19 48 30High nucleation,dendritic growth
3 5 5 19 72 20more opaquecrystals.
4 5 5 19 96 15Low nucleation,few opaque, fewtransluscent
5 5 5 19 120 10
Few transparent,prismatic andprismaticpyramidal awayfrom gel interface
6 5 5 19 144 7Low nucleationdensity, crystalssame as above.
7 5 5 19 156 4Few crystals,quality as above.
05
10152025303540
12 36 60 84 108 132 156Aging time (hours)
Num
ber o
f nuc
leat
ion
Fig. 5.7 : Effect of gel aging time on number of nucleation
129
5.5.4 Effect of concentration of reactants
To investigate the effects of concentration of feed solutions, gel
of same pH and density were prepared. Feed solution of KIO3 was
tried. KIO3 solutions of 0.1 M to 0.5 M were prepared. Similarly,
solutions of BaCl2 or Ba(NO3)2 having different molarities 0.01 M to
0.1 M and solutions of CdCl2 or Cd(NO3)2 having different molarities
0.1 M to 0.8 M were prepared. By keeping the molarity of reactants
incorporated in gel constant, say BaCl2 and CdCl2, feed solutions of
KIO3 having different molarities were put over the set gels. It was
observed that as the concentration of the feed solution increases, the
nucleation density also increases. This may be due to the enhanced
availability of K+ ions. After repetition of number of experiments,
suitable concentration of reactants, as BaCl2 and CdCl2 incorporated in
gel is found to be 0.05M and 0.5 M respectively and for the feed
solution, as KIO3, it was found to be 0.5 M. Once the optimum
condition was achieved, all the experiments were carried out by
incorporating be 0.05M BaCl2 and 0.5 M CdCl2 solution in gel and 0.5
M, 20 cc, KIO3 solution was poured over the set gel as a supernatant.
Table 5.6 reports the effects of concentration of reactants on habit,
quality, and size of single crystals.
130
Table 5.6 : Effect of concentration of reactants on habit quality andsize of BaCd(IO3)4 crystals
Concentration ofreactants in gel
Concentrationof reactantabove gel
Habit Quality Size (mm)
BaCl2 0.01 to 0.08M and CdCl2 0.1to 0.3 M (5 ml)
KIO3 0.1 to 0.5M (20 ml)
Dendritic Opaque,brittle
2 to 4 x 1
BaCl2 0.01 to0.08M and CdCl2
0.4 to 0.8 M (5 ml)
KIO3 0.1 to 0.3M (20 ml)
Dendritic Opaque,brittle
2 to 4 x 1
BaCl2 0.01 to0.04M and CdCl2
0.1 to 0.8 M (5 ml)
KIO3 0.1 to 0.5M (20 ml)
Dendritic Opaque,brittle
2 to 4 x 1
BaCl2 0.06 to0.08M and CdCl2
0.1 to 0.8 M (5 ml)
KIO3 0.1 to 0.5M (20 ml)
Dendritic Opaque,brittle
2 to 4 x 1
BaCl2 0.05 M andCdCl2 0.4 M (5 ml)
KIO3 0.4 M(20 ml)
Prismatic,Prismaticpyramidal
Good,transparent,few opaque
2 x 2 x 1.2 x 2 x 2
BaCl2 0.05 M andCdCl2 0.5 M (5 ml)
KIO3 0.5 M(20 ml)
Prismatic,Prismaticpyramidal
Good,transparent,few opaque
2 x 2 x 12 x 2 x 2
5.5.5 Concentration programming
After establishing the optimum conditions, experiments of
concentration programming were carried out in test tubes in order to
achieve nucleation control and improvement in the quality of the
crystals. For this purpose, BaCl2 solutions having molarities 0.01 to
0.08 M and CdCl2 solutions having molarities 0.1 to 0.8 M were
prepared. Gel solution was allowed to set and age. After sufficient
aging, 20 ml of 0.1 M KIO3 feed solution was slowly added. This feed
solution was replaced by another equal volume feed solution in next 48
hours. The change in feed solution was made in steps of 0.1 M. This
process was continued until the concentration of KIO3 reached 0.5 M.
With lower concentration of supernatant, no nucleation was observed.
131
After increasing the concentration, few nuclei were formed. Further
increase in concentration created very few nucleation centers and
helped the previous nuclei to grow to their optimum size. Slight change
in luster and morphology is observed. Hence, it can be said that
though it is not much useful, concentration programming is slightly
helpful in improving the quality of crystal.
5.6 Characterization
Mixed crystals of BaxCd1-x(IO3)4 grown were characterized by
XRD, FT-IR, SEM, EDAX, TGA, DTA and DSC.
5.6.1 X-ray diffraction
Excellent experimental verification for the crystal structures is
available through the X-ray diffractometry. When the high frequency
electromagnetic waves are selected to have wavelength comparable the
interplanar spacings of the crystals, they are diffracted according to
physical laws. X-ray diffractogram was recorded using RigaKu,
Miniflex, Japan with CuK radiation (1.5418Å) shown in Fig.5.8. The
observed d-values and hkl were computed. The computer program
POWD (an interactive Powder Diffraction Data interpretation and
Indexing Program version 2.2) was used to calculate ‘d’ values. Table
5.7 represents d-values and hkl values from the computer program. The
observed peaks in diffractogram shows that the mixed iodate crystals
possess monoclinic structure. Calculated unit cell parameters are given
in table 5.8. The atomic fraction x of Ba replacing Cd atoms is 0.3, as
calculated from the lattice parameters given in table 5.7 and employing
the Vegard’s law. The molecular formula of the crystals grown can
therefore be written as Ba0.3Cd0.7(IO3)4 the basis of XRD.
132
Fig.5.8 : X-ray diffractogram of barium cadmium iodate
Table 5.7 : d-values and hkl values from the computer program
Sys.MONO. Lambda= 1.540510a= 11.2978 b=10.8263 c= 8.3238 beta=92.174 V= 1018---------------------------------------------------------Line d-spacing A. Int. Indices 2Theta Deg.
obs. calc. obs. h k l obs. calc.---------------------------------------------------------
1 8.2687 8.2687 35 0 2 0 10.69 10.692 7.0304 7.0304 54 1 0 0 12.58 12.583 4.1163 4.1163 69 1 0 1 21.57 21.574 3.7872 3.7872 78 -1 0 2 23.47 23.475 3.4164 3.4359 54 0 0 2 26.06 25.916 3.1574 3.1655 100 -2 3 1 28.24 28.177 3.0153 3.0175 67 -2 2 2 29.60 29.588 2.5580 2.5581 50 0 6 1 35.05 35.059 2.2700 2.2701 51 -3 3 2 39.67 39.67
10 2.0018 2.0024 48 -1 5 3 45.26 45.2511 1.8175 1.8167 47 -4 0 3 50.15 50.1712 1.7140 1.7142 35 -3 7 2 53.41 53.4013 1.6050 1.6060 38 3 6 1 57.36 57.3214 1.4535 1.4541 25 -5 4 2 64.00 63.9715 1.2490 1.2492 24 -1 7 5 76.15 76.13
---------------------------------------------------------
133
Table 5.8: Calculated unit cell parameters
Parameter Ba(IO3)2 Cd(IO3)2 BaxCd1-x(IO3)4
SystemabcV
Monoclinic13.63 Å7.979 Å9.036 Å
982.69 (Å)3
Monoclinic5.856 Å17.470 Å5.582 Å
571.063 (Å)3
Monoclinic11.2978 Å10.8263 Å8.3238 Å1018 (Å)3
5.6.2 Fourier transform infrared (FT-IR) spectral analysis
Infrared spectroscopy is used for structural analysis. It quickly
provides useful information about the structure of molecules without
tiresome evaluation methods. This method solves many problems in
organic and co-ordination chemistry, while in some problems infrared
data advantageously complement the results obtained by other
methods. It gives information about modes of vibration of molecules.
A new method known as Fourier Transform Infrared
Spectroscopy (FT-IR) has come into use more recently. Light covering
the whole frequency range, typically 4000–400 cm-1, is split into two
beams. Either one beam is passed through the sample, or both the
beams are passed, but one beam is made to traverse longer path than
the other does. Recombination of the two beams produces an inference
pattern that is the sum of all the inference patterns created by each
wavelength in the beam. By systematically changing the difference in
the two paths, the inference patterns change to produce a detected
signal varying with optical path difference. This pattern is known as
interferogram, and looks nothing like a spectrum. However, Fourier
transformation of the interferogram, converts it into a plot of %
transmittance against wave number, which resembles the usual
spectrum obtained by traditional method. There are several advantages
134
of FT-IR over the traditional method. Because it is not necessary to
scan each wave number successively, the whole spectrum is measured
in at most a few seconds. Moreover, because it is not dependent upon
a slit and a prism or grating, high resolution in FT-IR is easier to obtain
without sacrificing sensitivity [20].
FT-IR is used for structural analysis. In the present study IR
spectrum of barium cadmium iodate sample was recorded using
SHIMADZU spectro-photometer at dept. of Chemistry, University of
Pune. Figure 5.9 shows FT-IR spectrum of barium cadmium iodate.
The IR spectrum was recorded in the wave number range 400-4000
cm-1 for KBr line.
Bands due to vibration involving metal, iodine and oxygen
atoms are found predominantly near 796.48 cm-1. Fundamental infrared
frequencies, observed in all iodate compounds in general, are also
found in present FT-IR analysis, which confirm the iodate group of
grown crystals. The bands at 390.14 cm-1 are due to iodate group.
Fundamental frequencies that have been observed are 1 (symmetric
stretching) at 746.48 cm-1, 3 (asymmetric stretching) at 804.34 cm-1
and 2 (symmetric bending) at 390.14 cm-1 and 4 (asymmetric
bending) at 337.12 cm-1. The dominant absorption bands are found at
700-815 cm-1 in all iodate compound (Nakamoto 1970).
135
Fig. 5.9: FT-IR spectrum of barium cadmium iodate
5.6.3 Scanning electron microscopy (SEM)
Scanning electron microscopy was carried out at NCL, Pune.
Figures 5.10, 5.11 and 5.12 show SEM images of powdered samples of
mixed barium cadmium iodate.
Fig. 5.10 : SEM image
x
136
Fig. 5.11 : SEM image
Fig. 5.12 : SEM image
Fig. 5.10 shows the part of the crystal of barium cadmium
iodate. It is observed that whole the face is almost dark and the face is
covered with rod shaped figures of different size. The rod shaped may
be due to the presence of cadmium. The magnified version of ‘x’ in
Fig. 5.10 is shown in Fig. 5.11.
y
137
Because of highest magnification, the rod structure in Fig. 5.10
seems to be slightly bright in the Fig. 5.11.
The magnifying version of ‘y’ in Fig. 5.11 is as shown in
Fig. 5.12. Again due to the higher magnification the same rod seems
to be more bright. The rods are seem to be of different size but
approximately of same shape.
5.6.4 Energy dispersive analysis (EDAX)
Elemental analysis was carried out at NCL, Pune. Table 5.9
shows values of elemental content of the crystal by EDAX and
theoretical calculation from molecular formula. From table it is clear
that the values (wt % and at %) of O, Ba, Cd and I in the grown crystal
measured by EDAX are very close with the values calculated from
molecular formula.
Table 5.9: Values of elemental content of the crystal.
Element
Content asmeasured by
EDAX
Content as calculated frommolecular formula
Ba0.3Cd0.7(IO3)4
wt % at % wt % at %OBaCdI
27.914.388.63
59.08
72.521.233.25
23.00
23.464.929.60
62.02
70.581.764.11
23.55
5.6.5 Thermal analysis
Thermal analysis, mainly, Thermo Gravimetry (TG), Differential
Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC)
are widely used in the investigation of both physical and chemical
phenomena. Numbers of reviews are available on applications of
thermo analytical methods [21-23].
In TGA, the study is based on the observation of weight change
as a function of temperature or time. In DTA and DSC, the study
138
depends on the measurement of difference in heat content of a sample
with reference to a standard substance as a function of temperature or
time.
TGA, DTA and DSC studies of mixed iodate crystals were
carried out at NCL, Pune. Figures 5.13, 5.14 and 5.15 represent the
TGA, DTA and DSC curve respectively. The initial 84 % weight loss
in the temperature range 200-330oC is due to decomposition of crystals
may be loss of iodine and some oxygen from the anhydrous mixed
iodate crystals. Again in the temperature range 6500C-7400C, there is
10 % weight loss indicating decomposition of reaction producing
mixture of BaO and CdO.
The calculation shows that the molecular formula of the grown
Ba0.3Cd0.7(IO3)4 crystal as determined from XRD.
DTA curve of the same compound shows its peaks at 2000C-
330oC and 6500C-7200C.
From DSC curve following explaination,
Step – I : The initiation temperature is 134oC and equilibrium
temperature is 150oC. At 134 oC (initiation temperature) initiation of
phase change start and phase change is completed at peak endo-down
tempearture 140oC (transition temperature). The temperature at which
the sample and reference come to the thermal equilibrium by thermal
diffusion appears to be at 150oC.
(i) Area under the curve is 260.597 mJ
(ii) Heat of transition ∆H i.e. enthalpy change of transition is
21.8989 J/gm which is 0.0219 KJ/mole. Since molecular
weight is 1 gm/mole. Therefore, ∆Htr = ∆Hf i.e. heat of
phase formation is also 0.0219 KJ/mole where ∆Hf is
enthalpy change of new phase formation or it is called Heat
of phase formation.
139
Step – II : At 290oC (initiation temperature) initiation of phase change
starts and the phase change (i.e. transition) at peak exo-up tempearture
321.9oC (transition temperature). The temperature at which the sample
and reference come to the thermal equilibrium by thermal diffusion
appears to be at 370oC.
(i) Area under the curve is -5413.844 mJ
(ii) Heat of transition ∆Htr i.e. enthalpy change of transition is -
454.94 J/gm which is -0.4549 KJ/mole. Since molecular
weight is 1 gm/mole. Therefore, ∆Htr = ∆Hf i.e. heat of
phase formation is also -0.4549 KJ/mole where ∆Hf is
enthalpy change of new phase formation or it is called Heat
of phase formation.
In the DSC study the one endothermic stage is obtained, but at
321oC an exothermic phase transition process was noticed. The
thermal effect is -0.0109 Kg/mol. The result of DSC measurements are
presented in the table 5.10. In this table the enthalpy have been
calculated from the graph.
Table 5.10: Values of ∆H and transition temperature Tr from DSC ofthe crystal.
SampleWt of thesample
Change inenthalpy
∆H
Transitiontemperature Tr
Bariumcadmiumiodate
0.0119 g0.0219 KJ/mole 139.80o C
-0.4549 KJ/mole 321.09o C
140
Fig.5.13: TGA curve of barium cadmium iodate crystal
Fig. 5.14: DTA curve of barium cadmium iodate crystal
141
Fig. 5.15: DSC curve of barium cadmium iodate crystal
5.7 Conclusions
From the above discussion, the following conclusions can be drawn:
1. Barium cadmium iodate crystals can be grown by using gel
technique.
2. Single diffusion gel growth technique is suitable for growing
crystals of barium cadmium iodate.
3. Different habits of barium cadmium iodate crystals can be
obtained by changing parameters like gel density, gel aging, pH of
gel, concentration of reactants, concentration of impurities etc.
4. Most suitable value of gel density is found to be 1.04 gm/cc.
5. Aging helps in controlling nucleation rate.
6. Suitable pH value for growth of these crystals is 4.0.
7. High concentration of reactants yields dendrites crystals. Low
concentration of reactants produces platy crystals, while proper
concentration of reactants yields prismatic and prismatic
pyramidal crystals. Some of them are transparent, while few of
them were mostly translucent at another end. The reason may be
the inclusion of gel in them.
142
8. Concentration programming plays very minor positive role in
improving quality of the crystals.
9. The observed peaks in diffractogram shows that the mixed iodate
crystals possess monoclinic structure.
10. The TGA calculation shows that the molecular formula of the
grown Ba0.3Ca0.7(IO3)4 crystal as determined from XRD.
11. Chemical compositions of the grown crystal by EDAX are match
with the theoretical calculation from molecular formula.
143
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