Crystal structure and lattice dynamics of chromium hydrides

Samples of fcc (γ) CrH and hcp (ɛ) CrH have been prepared by cathodic electrodeposition of chromium and studied by powder neutron diffraction at 8 K and by inelastic neutron scattering (INS) at 5 K in the range of energy transfers 6-400 meV. A profile analysis of the neutron diffraction patterns showed that hydrogen occupies octahedral interstitial sites in the fcc metal lattice of γ-CrH with a = 3.854(3) Å and in the hcp metal lattice of ɛ-CrH with a = 2.719(3) Å and c = 4.433(4) Å. No magnetic ordering was detected in either hydride at 8 K. The INS investigation demonstrated that the fundamental band of optical hydrogen vibrations in both hydrides consists of a strong peak with a broad shoulder towards higher energies. The peak position is 118 meV for γ-CrH and 122 meV for ɛ-CrH.