High-pressure structural phase transitions in CuWO4

We study the effects of pressure on the structural, vibrational, and magnetic behavior of cuproscheelite. We performed powder x-ray diffraction and Raman spectroscopy experiments up to 27 GPa as well as ab initio total-energy and lattice-dynamics calculations. Experiments provide evidence that a structural phase transition takes place at 10 GPa from the low-pressure triclinic phase P1 to a monoclinic wolframite-type structure P2/c. Calculations confirmed this finding and indicate that the phase transformation involves a change in the magnetic order. In addition, the equation of state for the triclinic phase is determined: V-0=132.8(2) angstrom(3), B-0=139(6) GPa, and B-0(1)=4. Furthermore, experiments under different stress conditions show that nonhydrostatic stresses induce a second phase transition at 17 GPa and reduce the compressibility of CuWO4, B-0=171(6) GPa. The pressure dependence of all Raman modes of the triclinic and high-pressure phases is also reported and discussed.