First-principles study the structural, electronic, vibrational and thermodynamic properties of Zr1−xHfxCoH3

The structural, electronic, vibrational and thermodynamic properties of Zr1−xHfxCoH3 (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) are investigated using first principles approach based on the virtual crystal approximation (VCA). The results indicate the series Zr1−xHfxCoH3 have the similar physical properties. When Hf concentration increases gradually, the lattice parameter reduces and the thermodynamic stability first decreases and then increases, respectively. The calculated results of charge distributions and electron localization function (ELF) suggest that the interactions of HCo and HZr1−xHfx are primarily metallic with a small covalent component. The band structure and the corresponding density of states (DOS) around the Fermi level (Ef) indicate the metallicity enhances and the electrical conductivity is better with increasing Hf content. The phonon density of states imply that with the increase of Hf content, the covalent interactions between H(4c2) and Zr1−xHfx are weakened, while the covalent interactions between H(8f1) and Zr1−xHfx basically remained unchanged (H(4c2) and H(8f1) represent the hydrogen atoms occupying 4c2 and 8f1 site, respectively), which is consistent with the results of charge density. Finally, the thermodynamic properties are obtained and discussed on the base of the obtained vibrational properties.