Electronic and magnetic structures and bonding properties of Ce2CrN3 and U2CrN3 from first principles

The electronic and magnetic structures of A2CrN3 (A = Ce, U) ternary compounds calculated within density functional theory (DFT) exhibit different behaviors of the nf elements (n = 4, 5 respectively). Charge analysis allows to formally express the two compounds as [A2Cr]∼5+ [N3 ]∼5− thus classifying them as covalent nitrides, i.e. far from formal exchange of ±9 electrons. From the establishment of the energy-volume equations of state, the two compounds are found with hardness magnitudes: B0(A = Ce) = 192 GPa and B0(A = U) = 243 GPa, within range of oxides due to covalent metal-nitrogen bonding described within overlap matrix analysis. The uranium compound is harder due to a smaller volume and less compressible U versus Ce metals. From relativistic spin orbit coupling calculations both compounds are found to exhibit finite magnetizations on Ce, U and Cr with opposite sign of A versus Cr and the long range magnetic order is identified as ferrimagnetic.