Quadrupole interactions in Zr${\mathrm{V}}_2$ hydrides

Hydrides of Zr${\mathrm{V}}_2$ ($\mathrm{Zr}{\mathrm{V}}_2{\mathrm{H}}_x$) were investigated using the NMR technique. Well-resolved quadrupole spectra of the ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ nuclei were obtained at room temperature. The quadrupole frequency ${\nu }_Q$ increases with hydrogen concentration from 20 kHz for $x=0\mathrm{} \left(\mathrm{Zr}{\mathrm{V}}_2\right) \mathrm{to} 330$ kHz for $x=3,4\mathrm{}$. The sharp structure of these spectra is destroyed at low temperatures. The behavior is explained by line narrowing due to the high rate of hydrogen diffusion at room temperature and the symmetry of the crystal lattice of the $\mathrm{Zr}{\mathrm{V}}_2{\mathrm{H}}_x$ compounds. Various line-broadening mechanisms are discussed. The Knight shift and spin-lattice relaxation time $T_1$ of ${}_{}{}^{51}{}_{}{}^{}\mathrm{V}$ were measured as a function of hydrogen concentration. $T_1$ is strongly hydrogen-concentration dependent due to changes in the dynamic part of the quadrupole interaction as well as to change in the electronic structure which is also manifested in the Knight-shift behavior. There is agreement between the quadrupole interaction derived from the $T_1$ data and that obtained from the quadrupole spectra. The possible sources of the quadrupole interaction are discussed.