A PHASE-TRANSITION OF AGI AT 150 K

Anomalies in the heat capacity curves of AgI have been detected near t he temperature of 150 K. Powder X-ray diffraction experiments have bee n performed in the temperature range 23-299 K. These anomalies were ob served for the specimens which experienced the alpha- to beta/gamma-ph ase transition (heated up to 773 K and then quenched to room temperatu re) but became unobservable in the subsequent heating cycles. The vari ous values (1.5, 13.0 and 4.1 Jmol(-1)) of the enthalpy of transition obtained depend on the thermal history. It can be considered that the anomaly is a transformation from the intermediate (high-pressure) phas e to the beta/gamma phase.