Thermal transport properties of hafnium hydrides and deuterides

The thermal conductivities of δ′-, δ-, δ+ε-, and ε-phase hafnium hydrides and deuterides with various hydrogen isotope concentrations (HfH_x, 1.48 ≤ x ≤ 2.03; HfD_x, 1.55 ≤ x ≤ 1.94) were evaluated within the temperature range of 290-570 K from the measured thermal diffusivity, calculated specific heat, and density. The thermal conductivities of δ′-, δ-, δ+ε-, and ε-phase HfH_x and HfD_x are independent of the temperature within the range 300-550 K and are in the range 0.15-0.22 W/cm K and 0.17-0.23 W/cm K, respectively; these values are similar to and lower than the observed thermal conductivities of α-phase Hf. The experimental results for the electrical resistivities of δ′-, δ-, δ+ε-, and ε-phase HfH_x and HfD_x and the Lorenz number corresponding to the electronic conduction, obtained from the Wiedemann-Franz rule, indicated that heat conduction due to electron migration significantly influences the thermal conductivity values at high temperatures. On the other hand, heat conduction due to phonon migration significantly affects the isotope effects on the thermal transport properties.