Hydrogen motion and site occupation in Ti 2CoH x(D x): NMR and neutron scattering studies

Abstract

Nuclear magnetic resonance measurements of the 1H and 2D spin–lattice relaxation rates R 1 for Ti 2Ni-type compounds Ti 2CoH 0.5, Ti 2CoH 0.9 and Ti 2CoD 1.0 have been combined with inelastic neutron scattering (INS) measurements of the H(D) vibrational spectra and neutron diffraction measurements for the same samples. The R 1 results for Ti 2CoH 0.9 and Ti 2CoD 1.0 give evidence for the existence of a fast H(D) motion with the characteristic jump rate of about 3×10 8 s −1 at room temperature, whereas for Ti 2CoH 0.5 such a fast motional process is absent. The results of the INS and neutron diffraction measurements suggest that the appearance of the fast hydrogen jump process in Ti 2CoH x (D x ) with x≈1 is related to the occupation of an additional type of interstitial sites by hydrogen atoms. While in Ti 2CoH 0.5, hydrogen atoms are found to occupy only the octahedral sites with Ti 6 coordination, a partial occupation of the tetrahedral Ti 3Co and Ti 2Co 2 sites by H(D) atoms (in addition to the nearly completely filled sublattice of the octahedral sites) has been revealed for Ti 2CoH 0.9 and Ti 2CoD 1.0. Possible paths of hydrogen jump motion in Ti 2CoH x (D x ) are discussed on the basis of the distances between the sites partially occupied by H(D) atoms.