Electronic properties of Ti-Nb-H and Ti-V-H systems

Abstract

The results of measurements of the specific heats of Ti-Nb-H and Ti-V-H systems are reported. The electron-phonon enhancement coefficient λ was estimated from magnetic susceptibility data to be 0.33. This value and the electronic specific heat coefficient γ were used to determine the bare density of states N( E F ) at the Fermi level. The dependence of N( E F ) on the conduction electron concentration indicates that the rigid band model is not applicable in this case. We therefore assume that these deviations are due to interstitial hydrogen. However, substitution of titanium by niobium or vanadium (up to 20 at.% V) leads only to band filling without any change in the band shape. On this simple basis and assuming that N(E) = h + ( h a )E we can describe quantitatively the dependence of the density of electronic states at the Fermi level. In conclusion we can state the following: 1. (1) the Fermi energy of the dihydrides lies close to the maximum of the density of states (this result can also be obtained by band structure calculations); 2. (2) a decrease in the hydrogen concentration results in a lower and broader peak in the density of states. The change in the density of states is due to the position of hydrogen states relative to the metallic states.