Ab initio thermo-elasticity of δ-MHx (M=Zr, Ti)

In the present work, we report the results of a systematic ab initio study of the thermo-elastic properties of δ-MH1.5 (M=Zr, Ti). This investigation serves three purposes: (i) Elucidate the fully anisotropic temperature dependent elastic constants of hydrides, (ii) address discrepancies in thermal expansion data reported in the literature and (iii) provide input data for thermodynamic-based phase-transformation modelling. Due to a reduced contribution from the vibrational free energy to the strain energy, in agreement with experimental observations we find that the temperature dependent stiffness of hydrides vary to a much lesser degree than the matrix. For δ-ZrH1.5, we further find that Zener’s anisotropy ratio varies with temperature. Regarding the linear thermal expansion, our results indicate that it is highly temperature dependent. With the exception of a few outliers, our DFT data concurs well with experimental data, if the temperature range over which it was measured is taken into account. [Display omitted] •We investigate the thermal expansion and elastic properties of δ-hydrides with DFT.•The elastic constants do not vary significantly with temperature.•Zener’s anisotropic ratio is temperature dependent for δ-ZrHx, but not for δ-TiHx.•The thermal expansion coefficient varies significantly with temperature.•Experimentally observed variations in the thermal expansion are discussed.