Phase transitions, electronic properties, and superconductivity in the systemV2ZrHx

We present experimental results for the magnetic susceptibility in the temperature range between 10 and 300 K and for the low-temperature specific heat in samples of nominal composition ${\mathrm{V}}_2\mathrm{Zr}{\mathrm{H}}_x$, $0<x\le 1.22$. These data are supplemented by results from x-ray diffraction experiments. We find that at low temperatures and for $x\lesssim 1.3$, ${\mathrm{V}}_2\mathrm{Zr}{\mathrm{H}}_x$ decomposes into ${\mathrm{V}}_2$Zr and ${\mathrm{V}}_2$Zr${\mathrm{H}}_{1.3}$. In ${\mathrm{V}}_2$Zr${\mathrm{H}}_{1.3}$, the coefficient of the electronic specific heat, $\gamma$, is ∼3.2 mJ/${\mathrm{K}}^2$ g-at. (for cubic ${\mathrm{V}}_2$Zr, $\gamma \sim 23$ mJ/${\mathrm{K}}^2$ g-at.) and the magnetic susceptibility at 10 K, $\chi \left(10\mathrm{} \mathrm{K}\right)$, is ∼1.8 × ${10}^{-4\mathrm{}}$ emu/g-at. [for cubic ${\mathrm{V}}_2$Zr, $\chi \left(10\mathrm{} \mathrm{K}\right)$ ∼3.9 × ${10}^{-4\mathrm{}}$ emu/g-at.]. Thus, a drastic reduction of the electronic density of states at the Fermi level is observed. Above 2 K, ${\mathrm{V}}_2$Zr${\mathrm{H}}_{1.3}$ is not superconducting (for cubic ${\mathrm{V}}_2$Zr, $T_c\sim 8.7$ K). Our results are discussed in the context of recent band-structure calculations for ${\mathrm{V}}_2$Zr.