THE INTERPLAY OF HIGHER-ORDER VIBRONIC COUPLING AND HOST-LATTICE STRAIN IN THE E-2(G) GROUND-STATE OF COPPER(II) ELONGATED OR COMPRESSED OCTAHEDRA

The coordination geometry of Cu2+ doped into the octahedral sites of s olid materials may vary between tetragonally elongated and compressed, very often superimposed by distinct orthorhombic distortion component s. The geometric deviation from the otherwise preferred D-4h elongatio n can be traced back to the presence of host site strains due to elast ic lattice properties or tiny distortions of the host polyhedra. Vario us examples are discussed on the basis of a simple and a more sophisti cated (including dynamic features) vibronic coupling model.