Electronic and Elastic Properties of RCo_5 and RCo_5H_n (R = La, Ce, Pr)

Density functional calculations of the enthalpy of formation, Delta H, elastic constants, C_ij, and polycrystalline moduli of hexagonal LaCo_5, CeCo_5, PrCo_5, and their orthorhombic ternary hydrides, LaCo_5H_4, CeCo_5H_3, PrCo_5H_4, are reported. All compounds are found to be metallic and ferromagnetic. The calculated magnetic moments agree well with those observed. The theoretical Delta H values are in excellent accord with measured values, indicating that the generalized gradient approximation for the exchange-correlation potential in density functional theory is capable of accurately modeling Delta H for such metallically bonded materials. The spin-dependent elastic constants and associated polycrystalline moduli provide insights into differences between parent and hydride elastic properties, and form the foundation for modeling defects, such as dislocations, and their impact on hydride kinetics.