Study of Anharmonicity in Zirconium Hydrides Using Inelastic Neutron Scattering and Ab-Initio Computer Modeling

The anharmonic phonon behavior in zirconium hydrides and deuterides, including epsilon-ZrH2, gamma-ZrH, and gamma-ZrD, has been investigated from aspects of inelastic neutron scattering (INS) and lattice dynamics calculations within the framework of density functional theory (DFT). The harmonic model failed to reproduce the spectral features observed in the experimental data, indicating the existence of anharmonicity in those materials and the necessity of further explanations. Here, we present a detailed study on the anharmonicity in zirconium hydrides/deuterides by exploring the 2D potential energy surface of hydrogen/deuterium atoms and solving the corresponding 2D single-particle Schrodinger equation to obtain the eigenfrequencies, which are then convoluted with the instrument resolution. The convoluted INS spectra qualitatively describe the anharmonic peaks in the experimental INS spectra and demonstrate that the anharmonicity originates from the deviations of hydrogen potentials from quadratic behavior in certain directions; the effects are apparent for the higher-order excited vibrational states, but small for the ground and first excited states.

Automated summary

The anharmonic phonon behavior in zirconium hydrides and deuterides has been investigated using inelastic neutron scattering and lattice dynamics calculations within the framework of density functional theory. The study found that anharmonicity in these materials originates from deviations of hydrogen potentials from quadratic behavior in certain directions and is apparent for higher-order excited vibrational states. Convolution of the eigenfrequencies with the instrument resolution qualitatively describes the anharmonic peaks in the experimental data.