JAHN-TELLER PHENOMENA IN SOLIDS

Abstract

▪ Abstract  Jahn-Teller phenomena encountered in oxides are reviewed briefly. High-spin Mn(III) in an octahedral site illustrates an ion with twofold orbitally degenerate σ-bonding orbitals having a quenched orbital angular momentum; octahedral V(III) and high-spin Co(II), as well as tetrahedral high-spin Ni(II), are examples of ions with threefold orbitally degenerate π-bonding orbitals that retain orbital angular momentum. Cooperative local deformations that are static give rise, below a transition temperature Tt, to a lowering of the lattice symmetry, anisotropic interactions, and the possibility of a ferromagnetism that is oriented in opposition to a magnetic field applied on cooling through the transition. Dynamic local deformations can influence the physical properties of a solid in a variety of ways. Of special interest is the influence of dynamic deformations at a cross-over from localized to itinerant electronic behavior in a mixed-valent system.