E-TYPE ORBITALS OF OCTAHEDRALLY CO-ORDINATED IONS

A study is made of the properties of a paramagnetic ion in an Eg orbital state interacting with a lattice. A general formulation is given, appropriate to any spin, and it is shown that, if the ion-lattice interaction is sufficiently great, for the low-lying levels a profound change occurs in the motion of the neighbours. This may properly be described as a dynamic Jahn-Teller effect. The nature of the motion is examined and it is suggested that the ion plus its neighbours acts as a non-linear scattering centre for incident thermal waves, and that there are local vibrations of comparatively large amplitudes at 'beat frequencies'. In any situation where this description is applicable it then appears to be a reasonable approximation to replace the ion plus lattice by a 'molecular model'.