Effects of 'random deformations' in the EPR spectra of Jahn-Teller Cu(D2O)(6) complexes in the mixed KND4Zn(SO4)(2) 6D(2)O Tutton salt

The EPR study of high quality mixed crystal K(ND4)Zn(SO4)(2). 6D(2)O shows that the doped Cu-63(D2O)(6) complexes exist simultaneously in two configur ations, differing by the directions of Jahn-Teller spontaneous deformation. This observation directly confirms the early supposition that the elongati on direction of the doped copper complexes is determined by the indirectly interacting monovalent cations. The high temperature EPR spectra have a 'powder-like' appearance and, at lo wer temperatures, a significant deformation of the resonant lines is observ ed. These effects are explained as a result of random deformations, introdu ced by the mixing of ND4+ and K+ ions on the electronic structure and dynam ics of the Jahn-Teller hexaaqua copper complexes. Internal deformations cha nge the complex rhombicity and parameters of the Jahn-Teller adiabatic pote ntial leading to their random spread. It is shown that in a low symmetry ca se, the statistic, symmetrical distributions of these parameters may lead t o the asymmetric distribution of g- and A-values, resulting in the asymmetr ic distribution of the EPR resonant fields. The proposed approach is confir med by the presentation of theoretical spectra calculated for the assumptio ns of randomly distributed EPR spectra parameters. These spectra reproduce well experimentally observed spectra in K(ND4)Zn(SO4)(2). 6D(2)O crystals. (C) 2001 Elsevier Science Ltd. All rights reserved.