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Anisotropic electrical conductivity and low-temperature phase transitions of the solid electrolyte Ag26I18W4O16

Results of measurements of electrical conductivity of single crystals of Ag26I18W4O16 in the temperature range 473-175 K show the existence of two first-order transitions at 246 and 197 K ; the phases are labeled alpha, beta, gamma in order of decreasing temperature. Wthin experimental error, the principal conductivity axes of the alpha phase are a, b and c* over its temperature range of existence. At 25oC, the principal conductivities are 0.120, 0.085, and 0.083 ohm-1 cm-1, respectively, and the average conductivity, 0.097 ohm-1cm-1, is 1.6 times the best value obtained from conductivity measurements on polycrystalline material. It is shown that the log10(sighma T) vs T-1 data for the alpha phase imply that the activation enthalpies of motion are temperature dependent. It is also likely that very few Ag+ ions are thermally excited from the immobile to the mobile category. The magnitude of the activation enthalpies of motion of the beta and gamma phases appear to be constant, and suggest that there is greater (possibly complete) order in the gamma than in the beta phase and greater order in the beta than in the alpha phase.

electrical conductivity ; solid electrolyte ; single crystal ; Ag26I18W4O16

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