The temperature dependence of the pressure switching of Jahn–Teller deformation in the deuterated ammonium copper Tutton salt

The pressure switch of the Jahn–Teller deformation direction in (ND4)2Cu(SO4)2·6D2O was investigated in the temperature range 130–320 K. Below 295 K, the new, pressure-induced phase, is stable under ambient pressure. Switching back is observed on heating to above 297 K. In the range 150–295 K a strong temperature dependence of the switching pressure (from 24 to 450 MPa) is observed. Below 150 K, the switching process is slow and a coexistence of two phases is observed. We conclude that the switch of the Cu(D2O)6 complex deformation direction is the Jahn–Teller response to the changes in the hydrogen bond system.