Structure in the Neutron Scattering Spectra of Zirconium Hydride

Abstract

Neutron double-differential cross sections of four polycrystalline samples of $\mathrm{Zr}{\mathrm{H}}_{x}$ with hydrogen-to-zirconium ratios ($x$) of 0.54, 1.03, 1.56, and 2.00 have been measured with high-energy resolution by downscattering of neutrons from initial energies of 171.5 and 244.8meV. Clear evidence of structure in the one-phonon optical peak of Zr${\mathrm{H}}_{2}$ is observed for the first time. This structure consists of two maxima located at energy transfers of 137 and 143 meV and a shoulder located at 154meV. Similar structure is indicated for the other hydride samples but it becomes less well defined as the hydrogen-to-zirconium ratio decreases. The observed structure is compared with predictions of a central-force model calculation by Slaggie, which includes the effects of interactions between hydrogen atoms. The widths of the hydrogen vibration peaks are found to depend upon the zirconium-to-hydrogen ratio as well as upon the momentum transferred in the scattering process.