Superconductivity of the Hydrides and Deuterides of HfV2

Current interest in the superconductivity of metal hydrides and deuterides has encouraged an investigation of the influence of hydrogen and deuterium absorption on the crystallographic and superconducting properties of the C15 (${\mathrm{MgCu}}_2$ ‐type) intermetallic compound, ${\mathrm{HfV}}_2$ . Room temperature absorption of hydrogen (H) and deuterium (D) by ${\mathrm{HfV}}_2$ at ${\text{2.5\hspace{0.17em}×\hspace{0.17em}10}}^6\hspace{0.17em}\mathrm{Pa}$ . was found to produce alloys of the compositions ${\mathrm{HfV}}_2{\mathrm{H}}_{\text{4.53}}\text{\hspace{0.17em}±\hspace{0.17em}0.02}$ and ${\mathrm{HfV}}_2{\mathrm{D}}_{\text{4.55}}\text{\hspace{0.17em}±\hspace{0.17em}0.02}$ which were stable upon removal to air. These fully hydrided and deuterated alloys were brought to equilibrium in various mixtures with ${\mathrm{HfV}}_2$ to produce a range of alloy concentrations. Within the limits of measurement, the lattice parameters of the hydrides and deuterides of the same concentration were found to be identical, and the lattice expansion arising from absorption was found to vary linearly with hydrogen or deuterium concentration. These specimens, which were powdered by the absorption process, were tested for superconductivity to the compositions ${\mathrm{HfV}}_2{\mathrm{H}}_{\text{1.59}}$ and ${\mathrm{HfV}}_2{\mathrm{D}}_{\text{1.00}}$ by an inductance bridge method. Alloying with hydrogen was found to decrease T_c by 4.7 K per mole of hydrogen per mole of ${\mathrm{HfV}}_2$ . The deuterides exhibit a more rapid decrease of T_c of 6.8 K per mole deuterium. Upper critical field measurements on ${\mathrm{HfV}}_2{\mathrm{D}}_{\text{0.5}}$ indicate a depression of H_c2 in comparison to ${\mathrm{HfV}}_2$ . These characteristics of the hydrides and deuterides are discussed on the basis of their lattice and electronic properties.