GROUP-THEORETICAL APPROACH TO ORBITAL ORDERING IN CRYSTALS WITH E(G) AND T(2G) IONS

Orbital ordering in crystals with degenerate localized levels E(g) and T2g is investigated on the basis of the symmetry of atomic density matrices and their transformation properties. During ordering processes, several kinds of local state can be stabilized, among which those with asymmetrical distribution of electron density are of practical importance. They are related to the E(g) x e(g), T2g x e(g), and T2g x t2g Jahn-Teller effects. In crystals with E(g) ions, the group-theoretical analysis leads to a large variety of possible ordered arrangements, whereas in those with T2g ions there are only a few symmetry-allowed configurations.