Phonon anomalies in transition-metal nitrides: ZrN

The phonon dispersion curves in superconducting ZrN have been measured in the highsymmetry directions $\Delta$, $\Sigma$, and $\Lambda$ by coherent inelastic neutron scattering at room temperature. Anomalies in the dispersion of the acoustic branches have been detected which are similar to those reported already for the superconducting transition-metal carbides and for TiN. The experimental results are well reproduced by a double-shell model which has also been used to calculate the phonon density of states. The calculated density is in good agreement with the results of time-of-flight measurements and with recent Raman data.