Heat capacities between 1.5 and 16 K and superconductivity of V/H and Nb/H alloys

Molar heat capacities have been measured for VH_n and NbH_n with n up to 1.93 at temperatures between 1.5 and 16 K. The height of the peak in plots of the electronic specific heat, indicating superconductivity, diminishes with increasing hydrogen content in the α + β two-phase region, and can be taken as a measure of the fractional amount of α-phase present (lever-rule). In NbH_n, accordingly, the two-phase region presumably extends up to n ≈ 0.9 at helium temperatures. No hydride phase, including VH₂ and NbH₂, showed superconductivity above 1.5 K.The measured γ-coefficients of the V/H-alloys agree with APW band-structure calculations for V metal in the range 5 ? n_e, ? 7 of band electron concentration. They coincide with the γ-coefficients of V/Cr-alloys reported in the literature. Hence VH_n represents another example of the “shifting bands” concept developed recently for PdH_n.