Specific heat anomalies and phase transitions in the solid electrolyte Ag26I18W4O16

摘要

Changes in the heat capacity of the solid electrolyte Ag26I18W4O16are measured in the temperature range 150ndash;330 K by differential scanning calorimetry. Our measurements, done on a powder sample, showed that Ag26I18W4O16has three phase transitions. AtT1quest;199 andT2quest;248 K, this material exhibits a first order phase transition with heat of transformationH1=53plusmn;2 mcal/g and H2=56plusmn;4 mcal/g. The phase transition atT3quest;277 K is second order with characteristic lambda shape. The transition atT1shows a broad onset and hysteresis (Dgr;Tquest;4 K). Similarly, the transition atT2is hysteratic but with Dgr;Tquest;1 K. No hysteresis is associated with the continuous orderndash;disorder transition atT3. It is concluded that Ag26I18W4O16becomes a superionic conductor at 277 K, in agreement with F. Habbal, J.A. Zvirgzds, and J.F. Scott lsqb;J. Chem. Phys. 69, 4984 (1978)rsqb; and not at 247 K, as erroneously concluded by S. Geller, S. A. Wilber, G. F. Ruse, J. R. Akridge, and A. Turkovic, Phys. Rev. B 21, 2506 (1980).