Structural phase transitions in Bi2V1−xGexO5.5−x/2 (x = 0.2, 0.4, and 0.6) single crystals: x-ray crystallographic study

Single crystals of Bi2V1−xGexO5.5−x/2 (x = 0.2, 0.4, and 0.6) were grown by slow cooling of melts. Bismuth vanadate transforms from an orthorhombic to a tetragonal structure and subsequently to an orthorhombic system when the Ge4+ concentration was varied from x = 0.2 to x = 0.6. All of these compositions crystallized in polar space groups (Aba2, F4mm, and Fmm2 for x = 0.2, 0.4, and 0.6, respectively). The structures were fully determined by single crystal X-ray diffraction studies.