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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')}
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Prosiding Pertemuan /lmiah Sains Materi 1997 ISSN 1410
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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
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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
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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-
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Prosiding Pertemuan Ilmiah Sains Materi 1997 /SSN /4/0 -2897
conducting NASICON (HZr2P3012) as well as
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ionic
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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.