Continuous changes of the Jahn–Teller deformation of Cu(H 2O) 6 complex in ferroelastic Cs 2Cu(ZrF 6) 2·6H 2O crystal

Abstract

Q-band EPR spectra of Cs 2Cu(ZrF 6) 2·6H 2O measured in temperature range 4.2–350 K and supported by the X-ray crystal structure analysis, show a gradual transformation of an adiabatic potential surface of the Jahn–Teller (JT) Cu(H 2O) 6 2+ complex leading to the switch of its elongation direction. This effect is joined with a ferroelastic phase transition at 320 K. It is shown that gradual movement of minima of the adiabatic potential surface along the φ coordinate for ρ≅ ρ 0, describing this phenomenon, is a result of a competition between a small lattice deformation at T> T c and the new deformation appearing at T c and increasing with decreasing temperature.