Pressure-induced phonon frequency shifts in transition-metal nitrides

Abstract

We report the first experiments on the high pressure phonon spectra of transition-metal nitrides HfN, ZrN, and NbN, obtained by Raman scattering measurements. Two pronounced bands, which are related to the acoustic part at low frequency around 200 cm${}^{-1}$ and the optical part at high frequency around 550 cm${}^{-1}$ of the phonon spectrum, respectively, shift to high frequency values with increasing pressure. An analysis of the results allows us to reproduce the experimental pressure dependence of the superconducting transition temperature $T_c$ of ZrN and NbN.

19 pages and 6 figures