RESEARCH AND DEVELOPMENT OF SUPERIONIC CONDUCTOR FORINDUSTRIAL APPLICA TION1

T. Sakuma2

ABSTRACTRESEARCH AND DEVELOPMENT OF SUPERIONIC CONDUCTOR FOR INDUSTRIAL APPLICATION. The

recent work about structural and dynamical properties of super ionic conductors by the X-ray diffraction, neutron diffraction andinelastic neutron scattering measurements was reviewed. The expression of the diffuse scattering intensity based on the correlationsamong the thermal displacements of atoms has been given and applied to AgBr and CuI. The presence of low-energy excitations incrystalline anion conductor CsPbCI3 was investigated by neutron inelastic scattering measurements. The application of superionicconductors to industrial use was introduced.

where flnc is the term due to the incoherent

scattering. The coherent term fCoh consists ofDebye lines and a diffuse scattering;

/Coh=/Oebye+/Oiffuse. (2)

The intensity of IOebye and IOiffuse are given as

IOebye = k!12G , (3)

IOiffuse= k ~n~n'exp{ iQ(Rn-Rn')}

Prosiding Pertemuan /lmiah Sains Materi 1997 ISSN 1410 -2897.uu,. ""V-~O71

volume, and Z, the number of sites belonging to thes' th j type neighbour around a sth i type site. S, isequal to sin(Qr)/Qr and hi the neutron scatteringlength. The probability of finding the atom in anysite, Pi, is equal to the ratio of the number of the iatoms to the number of the i sites in the crystal. TheDebye-Waller factor exp(-Mj) is equal to exp{-Bj(sin8/A)1. Two sites s(i) and s'(j) are apart by thedistance r. Typical superionic conductors have theaveraged structure in which the number of availableatomic sites is more greater than that of atoms.Probability functions

Prosiding Pertemuan I/miah Sains Materi 1997 ISSN 1410 -2897--,

250-1- ..&-~~

AgBrcalc

(b)200

~ 150e.!.~ 100""

S.s 50

The incident neutron energy of 41.0 meV was used.An oscillatory diffuse scattering of Cui at 8 K is notclear. However, an anomalously large andoscillatory diffuse scattering was observed from themeasurement at 290 K. The thermal parameterswere derived in the structure refinements using theintensity of the Debye lines obtained by the presentneutron diffraction measurement. The thermal

2parameters at 8 K; BI=0.02:l:0.73 A and BCu=0.18:l:

2 20.54 A , and at 290 K; BI=0.44:l:0.0l1 A and BCu=0.80:1:0.78 A 2 are used in the calculation of diffuse

scattering (Fig. 3). The values of the correlationterms Ar at 290 K are Ar s (Cu)s' (I) =0.6 at

2.5

Prosiding Pertemuan J/miah Sains Materi 1997 ISSN 1410 -2897

the TOF spectrometer LAM-40 installed at the pulsespallation neutron facility KENS. The range of Q(=41tsin8/A) covered by the spectrometer is 0.2-2.5

A -1. A low-lying dispersionless excitation near 1.8meV was observed in the inelastic scattering spectraof CsPbCl3 over the measured range of Q (Fig. 4).

Fig. 4. Observed inelastic neutron scattering spectra of

CsPbCl3 at Q=2.06 A-I.

The value of low-energy excitation is almostindependent of temperature. As the temperature islowered, the excitation near 1.8 me V becomes clearand the intensity of the inelastic scattering spectra inenergy around 1 meV decreases. If we apply therelation between the excitation energy and the massfor cation conductors to anion conductor CsPbCI3,the estimated .excitation energy is 4.6 me V for CIion. If we adopt the mass of Cs or Pb ions, theexcitation energy about 2.0 meV is derived. Thisresult would suggest that the excitation could be dueto an isolated vibrational mode of PbCl6 structural

unit.Further study of theoretical and experimental

treatments taking into account the contributions ofthe quasi-elastic scattering and the scattering arisingfrom the phonons or phonon-like excitations isnecessary to investigate the cause of low-energydispersion less excitatibns in superionic conductors.

INDUSTRIAL APPLICATION

Various kinds of applications can be devisedusing superionic conductors. Such devices arebased on electrochemical principles using the ionicconductor. In this chapter, recent work forindustrial applications is introduced.

A typical example of proton conducting oxidetinder hydrogen-containing atmosphere isSrCeO.9sYbO.OSO3-a. This material is a subs-tiruted solid solution based on the perovskite-typeoxide SrCeOj, in which S % of Ce are replaced byYb. Other perovskite-type oxides SrCeI-xMxO3-aand BaCel-xMxO3-a where M is some rare earth

element are also protonic conductors. Theseconductors can be used as materials for hightemperature devices. The devices are based onelectrochemical principles as a superionic conductordiaphragm: electrode/proton conducting diaphragm!electrode. High temperature protonic conductorsare applicable not only for sensors but also for highelectrolytic current usages; electrolysis, galvaniccell for power supply, etc. A bench-scale steamelectrolyzer was fabricated using one end closedceramic rubes made ofSrO.9sYbO.OS03-a.

NO is one of the polluting components fromcombustion engines and its removal is an importantproblem. Chemical catalysts have been mainly usedfor this purpose. However, this method is difficult

when engines are operated under the lean-burn (02-rich) condition. New methods are required for th~effective reduction of NO under lean-burnconditions. Removal of NO by electrochemicalreduction has been studying using a steamelectrolysis cell with platinum electrodes and aproton conductor SrZrO.9YbO.103-a.

There has been an increased demand for highenergy density batteries for mobile devices such asvideo cameras, portable computers and cellularphones. The popular lithium ion cell uses the veryexpensive LiCo02 cathode. Manganese oxides,such as LiMn204, are of particular interest becausethey readily intercalate lithium atoms into theirstructures. Lithium metal materials are generallyused as the anode materials for lithium rechargeablecells. The disadvantage of lithium metal is its shortcycle life; It is necessary to find a new anodematerial, which exhibits both a high specificcapacity and a long cycle life. Oxysulfide glassLi3P04-Li2S-SiS2 shows a high ionic conductivityat ambient temperature. It is chemically andelectrochemically stable against lithium metal.

Sensory detection of oxygenic gases such asCO2' NOx (NO and N02), and SOx (S02 and S03)

is important for protecting global as well as livingenvironments. An electrochemical cell usingNASICON (Na3Zr2Si2POI3' Na + conductor)

could detect S02 or CO2 provided that the cell wasattached with a layer of Na2S04 or Na2C03,respectively. A new group of superionicconductor-based electrochemical devices attachedwith a layer of auxiliary phase has been investigatedas attractive sensors for the detection of oxygenicgases. Zirconia-based sensing devices attached withan oxide electrode CdMn204 was found to be theexcellent material for NOx sensing. For the H2detection, a ZnO-attached device was found to giverelatively high sensitivity.

For selected humidity sensors based on proton-

9

Prosiding Pertemuan Ilmiah Sains Materi 1997 /SSN /4/0 -2897

conducting NASICON (HZr2P3012) as well as

REFERENCES

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Verlag., Berlin (1977).[5] SALAMON Ed. M. B.: Physics of Super ionic

Conductors, Springer-Verlag., Berlin (1979).

[6] CHOWDARI Ed. B.V.R.: Proceedings of the10th International Conference on Solid Statelonics, North-Holland, Amsterdam (1995).

[7] WASEDA Y.: Novel application on anomalous(resonance) X-ray scattering for structuralcharacterization of disordered materials,Springer-Verlag, New York, (1984).

[8] SAKUMA T., SUGIYAMA K.,MA TSUBARA E. and W ASEDA Y.: MaterialsTransactions, JIM 30(1989)365.

[9] SAKUMA T., SUZUKI F., SAITOH S.,SUGIY AMA K., MATSUBARA E. andWASEDA Y.: J. Phys. Soc. Japan62(1993)3513.

[10] MIYAKE S.: Diffraction of X-rays, KyoritsuPubl., Tokyo (1978).

[I I] SAKUMA T.: J. Phys. Soc. Japan61(1992)4041.

[12] SAKUMA T.: J. Phys. Soc. Japan62(1993)4150.

[13] SAKUMA T. and SAITOH S. : J. Phys. Soc.Japan 54(1985)3647.

[14] SAKUMA T., SHIBATA K. and HOSHINO S.: Solid State Ionics 53-56(1992)1278.

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sensors based on !}-Ca(PO3)2 has been studied.For monitoring HCI gas, strontium cerate (SrCeO3)doped with 10 mol% neodymium oxide (Nd203)and strontium chloride (SrC12) have been used.Yttria-stabilized zirconia (YSZ) thick films and bulkceria (CeO2) ceramics used as membrane electrodesare verified to work as high temperature pH sensors.

This work was supported by the Grant-in-Aid forScientific Research from the Ministry of Education,Science, Sports and Culture.