The Jahn-Teller cooperative effect in Cu1−xZnxSiF6 · 6H2O

Abstract The properties of CuSiF 6 · 6H 2 O and Cu 0.9 Zn 0.1 SiF 6 · 6H 2 O crystals were studied using X-Ray analysis and adiabatic calorimetry. The measurements cover the temperature range from 100 to 310 K. The enthalpy of transition for the phase transitions which occur at 300 K have been obtained and the crystal lattice parameters of the high-temperature phase of Cu 0.9 Zn 0.1 SiF 6 · 6H 2 O have been determined. These results furnish additional proof for the assumption that this transition involves the cooperative Jahn-Teller effect. The partial dehydration of specimens with loss of two water molecules in the phase-transition region, and the anomalous temperature dependence of the lattice parameters can be explained by stability loss of the initial phase over the pretransitional temperature range.