Heat capacity measurement and DSC study of hafnium hydrides

Heat capacities, electrical conductivities and phase transition temperature of hafnium hydrides, HfHx (0.99≤x≤1.83), were studied using a direct heating pulse calorimeter and a differential scanning calorimeter from room temperature to above 500 K. The heat capacity of HfH1.83 was larger than that of pure hafnium and showed no anomaly of heat capacity. In contrast, there were λ-type peaks for the heat capacity and DSC curves for HfHx (1.1≤x≤1.6) near 385 and 356 K. The anomalies of heat capacity and electrical conductivity of HfHx (1.1≤x≤1.6) were considered the result of phase transition and order-disorder phase transition for hydrogen in the hafnium hydride lattice for HfHx (1.1≤x≤1.3).