Jahn-Teller distortions induced by tetrahedral-site Fe2+ ions

Abstract

The Jahn-Teller effect for tetrahedral-site Fe2+ ions is expressed to second-order in the interaction energy and to lowest-order anharmonic vibrational energies. The formal results are identical to those for Mn3+ or Cu2+ ions in octahedral sites. However, interpretation of the parameters that enter the formal expressions shows that the mode and transition temperature of any static, crystalline distortion is much more strongly influenced by long-range elastic coupling in the case of tetrahedral-site Fe2+ ions. This result is used to interpret the absence of a static distortion from cubic symmetry in the spinel Fe[Al2]O4, for the occurrence of tetragonal ( c a < 1 and c a > 1) in chromium and vanadium spinels containing tetrahedral-site Fe2+ ions, and for the complex crystallographic properties of the system Fe3-xCrxO4. © 1964.