EXAFS study of pressure-induced phase transition in SrWO₄

Pressure-induced scheelite-to-wolframite structural phase transition in SrWO₄ was studied using two complementary techniques - x-ray absorption spectroscopy and x-ray diffraction (XRD). In situ XRD and W L ₃-edge EXAFS measurements were performed using the synchrotron radiation. The experiments were done at room temperature in the pressure range from 0 to 30 GPa using the diamond anvil cell. The XRD results unambiguously show that SrWO₄ transforms from the tetragonal scheelite phase to the monoclinic wolframite-type phase at about 11.7 GPa. Locally this transition appears as a change of the tungsten ions coordination from regular tetrahedral to distorted octahedral. The analysis of the EXAFS data suggests that tungsten ions displace from the centres of the tetrahedra by about 0.04 Å and some nearest oxygen atoms relax by about 0.23 Å.