Local structure in beta-Ti_1-y V_y H_x studied by inelastic neutron scattering

T. Ueda, S. Hayashi, Y. Nakai, and S. Ikeda
[Phy. Rev. B, Vol.51, No.9, 1 March, 1995-I]

The hydrogen sites in the disordered metal hydrides, beta-Ti_1-y V_y H_x(x ~ 1 and 0.2 lEy lE0.9) were studied using the incoherent inelastic neutron scattering (IINS) technique. The IINS spectra (shown in Fig. 1) of the hydrides were collected at 50 K. Four peaks originated from the b phase, whose energy ranges were 13 lEepsilon lE16 me V, 36 lEepsilon lE44 me V, 97 lEepsilon lE110 me V, and 134 lEepsilon lE152 me V. These peaks were assigned to the metal lattice vibrations and the local vibrational modes of hydrogen atoms occupying the octahedral site (0 site) and two kinds of tetrahedral sites (T₁ and T₂ sites), respectively. The ratio of the number of T₁ sites that were observed at the highest energy range to total hydrogen sites decreased and that of the 0 sites increased with increasing V content in the alloy. The composition dependence of the site fraction was analyzed using the cluster model modified to allow short-range ordering of metal atoms. The short-range order parameter was determined to be 0.43 ±0.05.

Fig. 1. Incoherent inelastic neutron scattering spectra of beta-Ti_1-y V_y H_x(x ~ 1 ; y = 0.2, 0.4, 0.6, 0.9) at 50 K. The spectra are normalized by the hydrogen concentrations, the total count, and the energy distribution of incident neutrons. The solid lines are the results of least-squares curve fitting of data with four Gaussians for y = 0.4 and 0.6 and with five Gaussians for y = 0.2 and 0.9, and the dashed lines are the background noise.