Theoretical study on the structural, electronic and physical properties of layered alkaline-earth-group-4 transition-metal nitrides AEMN2
Résumé
Thermodn., structural, and electronic properties of the layered ternary nitrides AEMN2 (AE = alk.-earth; M = group 4 transition metal) both with the KCoO2 and α-NaFeO2 structure-types are examd. within d.-functional theory. The AE:M at. (or ionic) radius ratio seems to be the most important criterion in detg. one structural arrangement over the other. We find that the majority of compds. are more stable with the KCoO2 structure-type where M is coordinated to five nitrogen atoms in a distorted square-based pyramidal geometry. Strong interactions occur in both arrangements not only between nitrogen and transition metal atoms, but also between nitrogen and alk.-earth metal atoms within and between the layers. Calcns. show that all the AEMN2 compds. with the tetragonal structure-type KCoO2 are semiconducting with band gaps of approx. 1 eV. However, small band gap conductor and even semi-metallic behavior are computed for compds. with the alternative hexagonal α-NaFeO2 structure-type.