EPR of dynamic Jahn-Teller distortion in Cu^II doped magnesium Tutton's salt

Abstract

The dynamic Jahn-Teller distortion in single crystals of Cu^II doped magnesium Tutton's salt, MgK₂(SO₄)₂·6H₂O was studied by EPR spectroscopy. The directions of the g tensor axes were found to coincide with those of A at room temperature as well as at 113 K and were correlated with the Mg---O directions in the lattice. Two spatially distinct sites of copper were detected in the crystal. The g and A values were also calculated from the polycrystalline samples at various temperatures. A dx²-y² ground state has been assigned for CuII, as in the isomorphous zinc Tutton's salt. The Silver and Getz model was applied to understand the dynamics of Jahn-Teller (JT) activity. The system was found to undergo dynamic JT distortion at all temperatures. At low temperatures, the [Cu(H₂O)₆]²⁺ ion has three possible degenerate vibronic states corresponding to three possible directions for the long axis of the octahedron. The energy separations between the three inequivalent JT valleys were estimated as ^δ1,2 = 90 and ^δ1,3 = 370 cm⁻¹. The lattice strain parameter V₂ and the JT stabilization energy E_JT were also estimated as 19,140 and 1030 cm⁻¹ respectively. From the E_JT value, the JT distortion present in the system was classified as a case of "strong" coupling.