EFFECT OF PRESSURE ON THE FAST-ION CONDUCTOR AGTLSO4

The a.c. electrical conductivity of AgTlSO4 has been measured at T between 365 K and 704 K and at P between 6.3 kbar and 49.5 kbar. The decrease in conductivity, sigma, with P and the diminishing sigma jump at the phase transition observed in our 1 atm DSC and dilatometric studies, are consistent with a simple volume-controlled cationic conduction mechanism. The shift of the transition to higher T with increasing P is in accord with LeChatelier's principle. The dependence of Q(c) on P for the high temperature phase is effectively linear for both heating and cooling. The Delta V-double dagger value of 16.4 cm(3) mole(-1) for the high temperature phase at 667 K between 6.3 kbar and 18.3 kbar is exceptionally high. Dilatometric traces recorded at 1 atm between 373 K and 523 K show an expansion of 1.47% at the similar to 465 K phase transition. Using the measured expansion and density of AgTlSO4, we obtain the enthalpy of transition Delta H-t = 25.7 kJ mole(-1) from the Clapeyron equation in fair agreement with Delta H-t determined from calorimetry.