Hydrogen in Nb(V 1− yCr y) 2 Laves-phase compounds: neutron diffraction and nuclear magnetic resonance studies

Abstract

In order to study the positions and mobility of hydrogen in ternary Laves-phase compounds Nb(V 1− y Cr y ) 2, we have performed neutron-diffraction measurements in NbVCr and NbVCrD 0.38 at T=295 K and nuclear magnetic resonance measurements of the 1H, 2D and 51V spin-lattice relaxation rates T 1 −1 in NbVCrH 0.3, NbVCrD 0.38 and NbV 1.4Cr 0.6H 0.6 over the temperature range 11–424 K. It is found that the host-metal lattice of both NbVCr and NbVCrD 0.38 has C15-type structure (space group Fd 3m ), and D atoms in NbVCrD 0.38 occupy tetrahedral g sites coordinated by two Nb atoms and two V(Cr) atoms. For all the samples studied, the temperature dependence of the motional contribution to T 1 −1 shows two peaks. This feature indicates a coexistence of two hydrogen jump processes with well-separated characteristic frequencies. The parameters of H(D) motion derived from the relaxation rate data for Nb(V 1− y Cr y ) 2–H(D) are compared with those for the related Laves-phase system TaV 2–H(D).