HEAT-CAPACITY ANOMALY IN THE HIGH IONIC CONDUCTOR RB4CU16I7CL13

The heat capacity of the high ionic conductor Rb4Cu16I7Cl13 was measured between 1 0 and 300 K using a high precision adiabatic calorimeter. An abnormal increase is observed in the heat capacity curve above 90 K, and the heat capacity value exceeds the classical limit value of 120R = 998 J K-1 mol-1 above 130 K. The excess heat capacity shows a broad anomaly with a maximum at about 190 K, which reveals a non-cooperative mechanism of the redistribution of Cu ions among the crystal sites. Heat capacity measurements were also made of Rb4Cu16I7.2Cl12.8, which showed a slight difference in the heat capacity.