Properties of Vanadium-Alloy Dihydrides

Abstract

Dihydrides of binary V-alloys with Ti and Cr have been investigated by X-ray diffraction, inelastic neutron scattering, measurements of the magnetic susceptibility and low temperature calorimetry. A strong H induced bulk segregation in V/Ti-alloys required special care in sample preparation. All dihydrides exhibit f.c.c. structure, the lattice constant decreases with decreasing Ti content, but remains almost unaffected by the Cr concentration. Inelastic neutron scattering shows only little dependence of the vibrational band modes on the alloy composition. Because the frequency range of the band modes and the local vibrations of H in the tetrahedra are widely separated, no contribution of the optical modes to the electron-phonon coupling and thus no superconductivity is possible. The local H frequencies (mean peak energies) of all the alloy dihydrides are lower than those of VH₂. The neutron scattering spectra of the V-alloy dihydrides show a structure in the peak of the optical modes (splitting). The steep rise of the dihydride electronic heat capacity as well as of the susceptibility is discussed in terms of band-structure calculations and reduced screening charge at the H site.