Electronic and elastic properties of RCo5 and RCo5Hn (R = La, Ce, Pr)

Density functional calculations of the enthalpy of formation, ΔH, elastic constants, Cij, and polycrystalline moduli of hexagonal LaCo5, CeCo5, PrCo5 and their orthorhombic ternary hydrides LaCo5H4, CeCo5H3, and PrCo5H4 are reported. All six compounds are found to be metallic and ferromagnetic. The calculated lattice constants, magnetic moments, and ΔH values are in very favorable accord with available experimental information. In each hydride, bonding is predominantly metallic with a small ionic component, as previous work indicated for LaNi5H7. Comparison of benchmark calculations of the elastic constants for orthorhombic TiSi2 with previous experimental and theoretical results for this compound confirms the validity of our computational approach for the RCo5 parent and hydride elastic constants. The results provide insights into differences between parent and hydride elastic properties