Metal−Metal Bonding and Metallic Behavior in Some ABO₂ Delafossites

We present results of ab initio band structure calculations on some ABO 2 delafossite oxides that have both the A and B sites occupied by transition metals. This class of materials includes insulators as well as some of the most conducting oxides. The calculations have been performed in order to understand the nature of the metallic and insulating states and the extensive metal−metal bonding displayed by these materials. The effect of polytypism on the electronic structure is examined. Among the interesting aspects of the electronic structure of these materials are the contributions from both A and B atoms to states near the Fermi energy and the highly disperse nature of bands derived from the d z 2 orbitals of the A atom. This last feature is expected to be important for stabilizing metallic ground states.