Rietveld study of the structural phase transition in the sanmartinite (ZnWO₄)-cuproscheelite (CuWO₄) solid solution

The P1̄ to P2/c phase transition in Cu_1-xZn_xWO₄ has been investigated by observing structural changes across the solid solution. The crystal structures of samples with x = 0.85, 0.55 and 0.30 have been refined by the Rietveld method from high-resolution synchrotron X-ray diffraction data. The Cu/Zn and W atoms are in distorted octahedral coordination. The microscopic order parameter (defined in terms and changes in Cu/Zn-O bond lengths) behaves in a similar manner to the previously-recorded macroscopic spontaneous strain. Rigid-unit-mode analysis shows that the transition does not involve distortions of a framework of rigid octahedra. Rather, the co-operative Jahn-Teller distortion of the CuO₆ octahedra is identified as the driving mechanism, with WO₆ octahedral distortions occurring as a secondary process. -Authors