Variable Temperature X-Ray Diffraction Study of Bismuth Magnesium Vanadate, BiMg2VO6

The space group for the structure of BiMg2VO6 at room temperature is shown to be Pmcn, rather than Amma as previously reported. However, when BiMg2VO6, is heated, its structure adopts the Amma space group at about 320 K. When the temperature is decreased through this transition, the (VO4)3- tetrahedron tilts, destroying one of the mirror planes in space group Amma. In space group Amma the (BiO2)1- chains have four equal Bi–O distances of 2.204 ? at 350 K. However, in the lower space group, there are two sets of Bi–O distances, 2.188 and 2.223 ? at 100 K. Unit cell edges in BiMg2VO6 increase with increasing temperature, giving an average linear thermal expansion of 5.2×10-6K-1 over the 100–350 K range.