Energy expression of the chemical bond between atoms in metal oxides Original Research Article

The chemical bond between atoms in metal oxides is expressed in an energy scale. Total energy is partitioned into the atomic energy densities of constituent elements in the metal oxide, using energy density analysis. The atomization energies, ΔEM for metal atom and ΔEO for O atom, are then evaluated by subtracting the atomic energy densities from the energy of the isolated neutral atom, M and O, respectively. In this study, a ΔEO vs. ΔEM diagram called atomization energy diagram is first proposed and used for the understanding of the nature of chemical bond in various metal oxides. Both ΔEM and ΔEO values reflect the average structure as well as the local structure. For example their values vary depending on the vertex, edge or face sharing of MO6 octahedron, and also change with the overall density of binary metal oxides. For perovskite-type oxides it is shown that the ΔEO value tends to increase by the phase transition from cubic to tetragonal phase, regardless of the tilting-type or the 〈1 0 0〉 displacement-type transition. The bond formation in spinel-type oxides is also understood with the aid of the atomization energies. The present approach based on the atomization energy concept will provide us a new clue to the design of metal oxides.