We investigate the nature of the interactions between defects in partially nonstoichiometric oxides and their rôle on some thermodynamic and transport properties.

Chemical diffusion in mixed ionic electronic conductors (MIECs) occurs via ambipolar motion. It finds many applications which are reviewed. The partial ionic and electronic conductivities are also of interest. Methods for determining these quantities are reviewed emphasizing problems with the Hebb-Wagner polarization method and suggesting an alternative method. The use of MIECs for probing simultaneously the ionic and electronic driving forces and for producing p-n junctions is discussed.

H3O+- and NH4 + -A12O3 polycrystals have been conductivity-optimised by eliminating metastable grain-boundary phases (NaA1O2 and MgAl2O4) and texturing the microstructure. The grain-boundary conductivity is considerably improved (up to 5x10-5(Ω-cm)-i) from 10–6 (Ω-cm)-l). The dc-field-assisted, H3O+ ion exchange process for K+/Na+-β"-A12O3 in HAC has been accelerated by cyclic switching of the dc field (cycle = 3secs) or injecting ultrasonic energy. The formeroubles the steady-state ion-exchange current to 12 μA by dispersing the HAC/electrolyte, interfacial, H3O+ polarisation layer. The ion-exchange currentefficiency is not improved from 0.15. The ultrasound (23 MHz) markedly shortens the time to complete ion-exchange (400 hrs.vs. > 700 hrs), more than doubles the final ion-exchange current (360 μA.vs. 150 μA) and improves the ion-exchange current efficiency to 0.24. These results are interpreted in terms of ionic “activation ”in the electrolyte. Evidence is presented of a mixed-cation-effect in H3O+-K-β"-AI2O3.

We report results of a nuclear magnetic resonance (NMR) study of lead(II) cations in β"-alumina. Measurements of line positions and spin-lattice relaxation times (T1) as a function of temperature are presented. The results show that Pb ions possess both static and dynamic disorder in low and intermediate temperature regimes, respectively. Also, a comparison is made between Lorentzian and logarithmic spectral density functions, from which we conclude that the latter provides a better fit to the dataat short correlation times (ωºτºα). The logarithmic form has been proposed to describe diffusive motion in 2-dimensional conductors.

Informations concerning electrical biassing effects on a medium are derived, usually, from the electrodes. Therefore, we frequently encounter phenomena which are peculiar to the electrode—medium interface(s), besides those due to bulk properties. In this report naive aspect on intrinsic biassing effects at the interfaces was presented first; then, as one of extrinsic origins, the mechanism of silver injection into glass from the silver anode was discussed.

Thin film amorphous electrolytes with compositions xLi2O:ySiO2:zP2O5 were deposited by single and dual source rf magnetron sputtering and their compositions determined by electron and ion beam techniques. Films containing P but no Si were composed of mainly orthophosphate and some linear chain phosphate anions, whereas single phase films containing Si and P were evidently composed of branched and possibly cyclic and extended network structures. Films with Si/P > 1 appeared to contain two or more amorphous phases. In the range of compositions investigated, the lithium ion conductivity depends mainly on the lithium ion mobility which is sensitive to the structure of the films. An open circuit voltage from 1 to 3 V measured between blocking metal contacts on the electrolyte thin films suggests that the films mightbe electrets.

Thin films of an amorphous lithium-conducting electrolyte were deposited by rf magnetronsputtering of ceramic targets containing Li4SiO4 and Li3PO4. The lithium content of the films was found to depend more strongly on the nature and composition of the targets than on many other sputtering parameters. For targets containing Li4SiO4, most of the lithium was found to segregate away from the sputtered area of the target. Codeposition using two sputter sources achieves a high lithium content in a controlled and reproducible film growth.

Basing on impedance and NMR spectroscopy data it is shown that there are two types of lithium ion motion in the each polymorhic modification of the Li3 Sc2 (P04)3 and Li3 In2 (P04)3 solid electrolytes. First type is a translational motion of these ions which determines the a values, while the second one is Li ion motion within the lithium ion—ion pairs at the distance about the sum of two lithium ionic radii. Substitution of 7Li by 6Li leads to the mixed alkali effect—type behaviour of σ.

Crystallographic results on the Li4-3x(Al,Ga)xSiO4 solid solutions are reviewed. The six sets of sites available for Li+ ions fall into two groups. The ‘framework’ sites, which also contain the substitutional Al,Ga ions, appear to have little effect on conductivity. The ‘channel’sites contain varying amounts of Li+ ions and are responsible for the dramatic variations in conductivity with x. There is evidence for the presence of one—dimensional defects, comprising columns of ordered Li+ ions, in both the framework and channel sites. The relative numbers of these linear defects has a large bearing on the solid solution mechanism in the framework sites and their occurrence in the channel sites may be responsible for the low conductivity in stoichiometric Li4SiO4.

Comparative neutron diffraction experiments have been performed on metal-halide MX (M = Ag, Li, Na; X = CI, Br, I) doped oxide glasses and their corresponding low conducting host glasses, e.g. M2O-2B2O3 and MPO3. The experiments reveal large changes in the intermediate range structure as the dopant salt is introduced, whereas the short range order of the host matrix is virtually unaffected by the dopant salts. An extra peak at anomalously low Q values (Q = 0.7-0.8 Å-I) appears in the structure factors of the silver-halide glasses which indicates the building up of a new type of intermediate range ordering with a characteristic length of 8-10 Å. The observation is tentatively ascribed to a-microscopic biphase system consisting of an expanded hosi glass network, unaffected on a microscopic scale, in which the silver-halide tends to form microclusters within the voids. In contrast, sodium- and lithiumhalides do not give rise to distinct new features in the structure factor. Instead a considerable smearing out of the first sharp diffraction peak of the host glaiss is observed. This indicates a partial breakdown of the intermediate range ordering of the host matrix. The results are discussed in relation to structure-conductivity models suggested for superionic glasses.

The synthesis, characterization, and electrochemical properties of sulfide-based lithiumglasses are briefly reviewed. Of the many probes that have been used to study these materials two will be discussed in more detail, namely solid state NMR and conductivity measurements at high frequency (106-109 Hz). Solid state NMR is particularly useful in understanding the network structure of these glasses and the role coformers play in modifying the glass network. Electrochemical measurements, including impedance at high frequency, give information concerning dynamic processes, and show that someof these glasses are potentially useful in miniature and thin-film solid state batteries.

A quasi-elastic neutron scattering (QENS) study of the Ag+-ion diffusion coefficient, D, in glassy (Ag2S)0.5 (GeS2)0.5 has been performed. The results indicate that the magnitude of D is larger, and its activation energy is smaller, than the corresponding quantities inferred from measurements of the d.c. ionic conductivity. This behaviour is ascribed to the fact that QENS probes diffusive processes occurring at very high frequencies (∼1011Hz) where the magnitude of the a.c. conductivity is correspondingly larger, and its temperature dependence is less, than that of the d.c. conductivity.

The behavior of AgReO4 under pressure has been studied in a diamond anvil cell. The equation of state determined by synchrotron radiation shows considerable change in compressibility with increasing pressure. X-ray and Raman scattering show a first-order phase transition from the scheelite to an as yet undetermined structure at 13 GPa. Changes in both the internal and external Raman active modes suggest a change in Re coordination. Optical transmission experiments demonstrate that the energy gap in the scheelitephase decreases at the rate of 75 meV/GPa. There is a small jump in the energy gap at 13 GPa, probably related to the structural transition. AgReO4 remains aninsulator to at least 47 GPa.

Thin films of vitreous solid electrolyte in the boron-oxide/lithium oxide system have been grown using a thermal evaporation technique. Solid electrolyte films of composition B2O3-xLi2O with 0.5≤x≤5 are obtained from a mixture of lithium metaborate and lithium oxide in good proportion. Structure and ionic conduction are studied as a function of the glass modifier concentration and process conditions. The structure is investigated by the mid-infrared absorption spectroscopyof films deposited on a silicon wafer. Comparison with bulk materials whose structures are known shows that the films have a similar structure, and exhibit the transformation of boroxol rings into triborate or di-triborate units as the Li2O concentration increases. The ionic conductivity has been studied over wide frequency and temperatureranges using the complex impedance spectroscopy in a sandwiched geometry. The ionic conductivity increases with increasing Li content and exhibits a maximum value for B2O3-3Li2O.

We have determined the displacements of the ions and the changes in cell parameters which occur on application of an electric field to a crystal of AgGaS2, using a three-step modulation method. The shifts in Bragg angle of 14 reflections, due to a fieldof 2.6 x 106 V/m applied nearly parallel to [221], were used to refine the change in cell parameters. The resulting piezo-electric coefficients are d14=d25 =8.8 (0.9) 10-12 C/N and d36=7.6 (1.8) 10-12 C/N. This leads to a value of 4.8 (0.5) pC/Nfor the piezoelectric constant in the [221] direction which compares well with a value of 5-6 10-12 C/N determined by other methods. The ionic displacements were studied on a second sample, with E=2.6x 106 V/m in adirection parallel to [110]. Very small, but significant a and b directiondisplacements were observed for all atoms, whereas the displacements in the c direction were negligible as expected. Relative to the sulfur framework, the Ga ion displacement is considerably larger than that of the Ag ions.

A structure earlier reported for K3NdSi6O15 suggests the possibility for fast—ion conduction by virtue of K+ ions which not only reside in connected channels, but which also display very large thermal vibration amplitudes. No properties of the phase had heretofore been examined. Crystals up to 2mm inlength have been synthesized under a variety of hydrothermal conditions. Refinement of the structure with single crystal x-ray data to a residual of 8.3% confirms the composition and structure of our crystals and reveals a very high thermal vibration amplitude along c for K+ ions which reside in interconnected [001] channels.A reversible phase transformation has been discovered at 180ºC with a heat of transformation of 4J/g. Preliminary measurements of the conductivity of the high temperature phase yield a preexponential factor of 3.4/cm and an activation energy of 0.61ev along [001], indicating that this compound is not a particularly good fast—ion conductor.

We describe a method for a simultaneous measurement of the total and electronic conductivities of solid electrolytes (SE). The total conductivity is determined by a four probe method and the electronic (electron/hole) conductivity is determined simultaneously by a two probe method, for samples having the van—der—Pauw configuration.

This article summarises ionic conductivity and structural studies in the sodium—ion conducting systems NaxM'x/2M'' 2-x/2O4, 2 ≥ x ≥ 4/3 and (M',M'')(Zn,Si), (Be,Si) and (Zn,Ge). The best conductors are found at x ≈ 1.75–1.85, with conductivities in the range 10-2–10-3 (Ωcm)-1 at 600 K. They exhibit stuffed cristobalite type structures, isotypic with the structure of orthorhombic Na2BeSiO4. Based on single crystal data, the Na2BeSiO4 structure has been determined and refined, bothat 295 and 623 K. The structures of several other isotypic compounds have been refined by the Rietveld method, including Na1.8(Zn0.8.Ga0.2)MO4 with M = Si,Ge and Nal.8 Be0.8Si1.1O4. The ionic conductivity properties of the materials are discussed in relation to the obtained structural data.

The electrical conductivity of perovskite—structured KTaO3 crystals acceptor doped with Co, Cu or Fe was investigated after treatments in oxidizing and reducing atmospheres under both wet and dry conditions. Isotope effect measurements (using H2O vs. D2O) show that, after treatments in wet gases of low P(O2), all the crystals are primarily protonic conductors, through a process of proton hopping with an activation energy close to 0.84 eV. Electron hole conduction dominatesat high P(O2) in the case of Fe and Cu doping. For Co—doped crystals, the conductivity is independent of P(O2) up to 1 atm., indicating that ionic conduction predominates. There is no evidence of oxygen vacancy migration, leading to the conclusion that the activation energy for that process Is relatively high.

Ba6Ta2O11 with an oxygen—deficient perovskite—related structure, was prepared through solid state reaction of BaCO3 and Ta2O5 powders. The electrical conductivity of sintered Ba6Ta2O11 pellets was measured by a.c. impedance spectroscopy inthe temperature range between 200 and 800ºC. The conductivity at 800ºC was3.7x10-3 Ω-1 cm-1; the activation energy for bulk conduction was 0.93 eV at temperatures between 500 and 800ºC and 1.22 eV below 500ºC. The bulk conductivity was independent of atmosphere, while the grain boundary conductivity, with an activation energy of 1.08 eV, decreased as oxygen partial pressure increased. The oxygen ion transport number obtained from concentration cell measurements was 0.5 to 0.65 at temperatures from 450 to 820ºC.