Heat of formation and band structure of binary and ternary metal hydrides

The heat of formation, , of metal hydrides is empirically found to be linearly related to a characteristic energy of the electronic band structure of the host metal. Independently of the position of the host metal in the Periodic Table (simple metals, noble metals, transition metals, actinides, and rare earths) we found = +, with =E₅-Eₒ, =29. 62 kJ/eV mol H, and =-135 kJ/mol H (E₅ is the Fermi energy and Eₒ is the center of the lowest band of the host metal; is expressed in kJ/mol H and in eV). Assuming that this relation also holds for ternary metal hydrides we used the (simple) tight-binding coherent-potential-approximation model of Cyrot and Cyrot-Lackmann to evaluate the characteristic energy of Aₘ₀Bₘ₁ alloys where A and B are both nonsimple metals. The values of derived from the calculated are in good agreement with existing experimental data on the heat of formation of ternary metal hydrides.