The depression of the dynamic Jahn‐Teller effect

Abstract

The Depression of the Dynamic Jahn-Teller Effect BY R. L. DAVIDOVICH (b) A.M. ZIATDINOV (a), M. M. ZARIPOV (a), YU.V. YABLOKOV (a), and The phenomena connected with the Jahn-Teller distortion of complexes in the presence of degenerate electronic states result in consequences important in solid state physics (1, 2) . The study of transitions between the potential minima of Jahn-

Dynamic Behavior of the Jahn−Teller Distorted Cu(H2O)62+ Ion in Cu2+ Doped Cs2[Zn(H2O)6](ZrF6)2 and the Crystal Structure of the Host Lattice

“…The thermal behavior of the EPR spectrum of Cs 2 {Zn[Cu](H 2 O) 6 }(ZrF 6 ) 2 has some features in common both with those reported for the Cu 2+ doped Tutton salts 3,5,6 and with those of Cu 2+ doped [Zn(H 2 O) 6 ]XF 6 , X = Si and Zr. , The Cu 2+ doped Tutton salts show a smooth convergence of just the two higher g -values in the temperature range 50−300 K, with the signals progressively broadening as the temperature rises. The lowest g -value of the Cu(H 2 O) 6 2+ ion in the Tutton salt host does not change below ∼300 K because the lattice strain interaction has a large negative component (corresponding to a compression of the octahedral site) acting along one of the metal−ligand bond directions, so that the vibronic wave function corresponding to the axial elongation of the bonds along this direction is too high in energy to be thermally populated at room temperature. ,, The convergence of the two higher g -values is due to thermal population of the vibronic wave function localized largely in the second minimum of the warped Mexican hat potential surface, with the rate of exchange between the wave functions always being so rapid that the signal corresponds to the weighted average of the two wave functions .…”

“…The g -values at room temperature were obtained from single-crystal spectra. The direction corresponding to the largest g -value, g ma x = 2.506 at 4.2 K, is parallel to the Zn−O(2) bond (the longest in the Zn(H 2 O) 6 2+ complex (see Table )) and is larger than that observed in Tutton salts and hydrates of trigonal symmetry. ,− That direction associated with the intermediate value, g int = 2.100, is parallel to the shortest Zn−O(3) bond, while that parallel to the lowest, g low = 2.077, corresponds to Zn−O(1). At low temperature, the spectra are thus characteristic of a g -tensor of near axial symmetry.…”

“…At 4.2 K, the rate of exchange between the three lowest energy levels is relatively slow, and the EPR spectrum is the superposition of the three spectra of the three lowest vibronic wave functions. Each has a g -tensor corresponding to a tetragonally elongated octahedral coordination geometry but with the long bonds along a different axis. − When the temperature is raised, the signals broaden and almost disappear in the region 30−60 K, where the rate of exchange is comparable to the EPR time scale. Above ∼60 K, the g -tensor is quite isotropic because the rate of exchange between the three vibronic wave functions becomes more rapid than the frequency difference between their EPR signals so that an exchange-averaged spectrum is observed.…”

“…In this case, the complex undergoes little change in geometry with temperature. The model was subsequently applied to the EPR data for the Cu(H 2 O) 6 2+ ion doped into a range of zinc(II) host lattices, in particular, the Tutton salts of general formula (cation) 2 [Zn(H 2 O) 6 ](SO 4 ) 2 , where cation represents NH 4 , Cs, Rb, and K, and related compounds . In these lattices, the EPR data suggest the copper(II) complex has the more common tetragonally elongated geometry with a significant orthorhombic distortion.…”

The Lattice Structure Parameters and Configuration of Cu2+ Jahn‐Teller Centres in Tutton Salt Crystals

“…I n this respect the integral mobility technique [5] is more preferable because the experimental set-up is rather simple in this case. Such measurements were carried out with n-type Si samples [6,7]. n-type Ge was investigated only a t dc field and two microwave frequencies [4] and there is no experiment with p-type Ge in a wide frequency range.…”