Specific heat of β-AgI single crystal at low temperatures

Abstract

Using high resolution AC calorimetry between 10 and 300 K, we measured the specific heat of AgI single crystal grown at room temperature in the hexagonal (β) phase. In addition to the previously reported thermal anomaly at T 1∼60 K, a second peak in the specific heat was observed at T 2∼220 K. Although the thermal signal at T 1 was reversible and shows no dependence on the thermal history of the sample, the peak at T 2 was enhanced on successive temperature scanning of the sample through the transition point until it reached a constant area (enthalpy) of about 4.15 J mol −1. We discuss our observations near 220 K in terms of a phase transition in the silver ion sublattice in β-AgI due to disordering of the mobile ions on heating the sample through the transition temperature.