Isotope effects in thermal diffusivity and electrical resistivity of zirconium hydride and deuteride

Thermal diffusivities of ε-phase zirconium hydride and deuteride (ε-ZrH_x and ε-ZrD_x: x = 1.69–1.99) have been measured at the temperatures from room temperature to 600 K by means of a laser-flash method. The hydrogen concentration and temperature dependences on the thermal conductivities of ε-ZrH_x and ε-ZrD_x have been estimated from the experimental results of the thermal diffusivity and the literature data of the specific heat and the density. It has been found that the thermal conductivity of ε-ZrH_x is higher compared with that of ε-ZrD_x. In order to understand the isotope effect of the thermal conductivity, the electrical resistivities of ε-ZrH_x and ε-ZrD_x have been measured using a four-contact DC method and their electrical conductivities have been obtained. Based on the Wiedemann-Franz rule, the comparison between the thermal and electrical conductivities shows that the electronic heat conduction is dominant for ε-ZrH_x and ε-ZrD_x at high temperatures around 600 K and the isotope difference in the thermal conductivity for x >1.8 is due to the difference in the electron-phonon scattering by optical mode.