Electronic structure of zirconium hydride: A proton NMR study

The proton spin-lattice relaxation times (T1) and Knight shifts (sigma/sub K/) have been measured as a function of temperature in fcc (delta phase) and fct (epsilon phase) ZrH/sub x/ for hydrogen concentrations 1.5< or =x< or =2.0. Interactions with the conduction electrons were found to be the only important T1 relaxation processes below 320 K for the high-purity ZrH/sub x/ samples, and no anomalous temperature effects were observed between 320 and 100 K. The dominant hyperfine interaction for the protons was the transferred core-polarization term from the Zr d band. Both (T/sub 1e/T)/sup -1/2/ and sigma/sub K/ indicate that the density of electronic states N(E/sub F/) at the Fermi level is very dependent upon hydrogen content with a maximum occurring near ZrH/sub 1.83/. This behavior is ascribed to modifications in N(E/sub F/) through the fcc-fct distortion associated with a Jahn-Teller effect in the d bands. The proton NMR results are consistent with a recent band-theory calculation of fcc ZrH2 and photoemission spectroscopy studies of ZrH/sub x/ when the changes in d bands caused by the Jahn-Teller tetragonal distortion are included. The fcc-fct distortions and electronic structures of the ZrH/sub x/ phases are compared with the corresponding properties of the TiH/sub x/ system