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 (P1̅) 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.