Electronic structure of zirconium hydride: A proton NMR study

Abstract

The proton spin-lattice relaxation times ($T_1$) and Knight shifts (${\sigma }_K$) have been measured as a function of temperature in fcc ($\delta$ phase) and fct ($\epsilon$ phase) $\mathrm{Zr}{\mathrm{H}}_x$ for hydrogen concentrations $1.5\le x\le 2.0$. Interactions with the conduction electrons were found to be the only important $T_1$ relaxation processes below 320 K for the high-purity $\mathrm{Zr}{\mathrm{H}}_x$ samples, and no anomalous temperature effects were observed between 320 and 100 K. The dominant hyperfine interaction for the protons was the transferred core-polarization term from the Zr $d$ band. Both ${\left(T_{1e}T\right)}^{\frac{-1\mathrm{}}{2}}$ and ${\sigma }_K$ indicate that the density of electronic states $N\left(E_F\right)$ at the Fermi level is very dependent upon hydrogen content with a maximum occurring near Zr${\mathrm{H}}_{1.83}$. This behavior is ascribed to modifications in $N\left(E_F\right)$ through the fcc-fct distortion associated with a Jahn-Teller effect in the $d$ bands. The proton NMR results are consistent with a recent band-theory calculation of fcc Zr${\mathrm{H}}_2$ and photoemission spectroscopy studies of $\mathrm{Zr}{\mathrm{H}}_x$ when the changes in $d$ bands caused by the Jahn-Teller tetragonal distortion are included. The fcc-fct distortions and electronic structures of the $\mathrm{Zr}{\mathrm{H}}_x$ phases are compared with the corresponding properties of the $\mathrm{Ti}{\mathrm{H}}_x$ system.