Structure Solution of the High-Pressure Phase of CuWO4 and Evolution of the Jahn-Teller Distortion

In this work, we have investigated the structural behavior of cuproscheelite up to 33.9 GPa by means of high-pressure single-crystal X-ray diffraction (SXRD) and extended X-ray absorption fine structure (EXAFS). According to EXAFS, beyond 9 GPa a phase transition takes place. On the basis of SXRD, the transition is from the triclinic (PI) structure to a monoclinic (P2/c) structure isotypic to wolframite. The transition implies abrupt changes of CuO6 and WO6 octahedra, but no coordination change. Further, we report the role played by the Jahn-Teller distortion of the CuO6 octahedra on the mechanism of the phase transition as well as the changes in the behavior of the Cu-O bonds for the triclinic and monoclinic phases of CuWO4. A second phase transition was detected at 22.5 GPa. Finally, a low-temperature experiment has been carried out at 100 K. No structural changes were detected for CuWO4, confirming the already known triclinic structure stability at room pressure and low temperature.