Polymorphism in PbBiOXO4 compounds (X=V, P, As). Part I: Crystal structures of α- and β-PbBiOVO4

Reinvestigation of PbBiOVO4 thermal behaviour revealed a phase transition. As shown by single-crystal X-ray diffraction and high-resolution neutron powder diffraction, α-PbBiOVO4 transforms to β-PbBiOVO4 at 550 °C. At 25 °C, α-PbBiOVO4 is triclinic, S.G. P-1, Z=2, with a=5.6088(3), b=7.1109(3), c=7.2978(3) Å, α=108.957(2), β=111.889(2), and γ=94.833(2)°. Above 550 °C, β-PbBiOVO4 is monoclinic, S.G. C2/m, Z=4, with a=13.61(1), b=5.64(1), c=7.18(1) Å, and β=113.75(1)°. Both structures are built upon (O2Bi2Pb2)∞ chains parallel to the [100] direction in the α polymorph and [001] in the β-polymorph. These chains are undulated in α and linear in β. In both structures, VO4 tetrahedra are organized in two sets of rows parallel to (O2Bi2Pb2)∞ chains, thus building layers of (OBiPb) sandwiched by two layers of VO4 oriented head to tail; VO4 displays different orientations in α- and β-PbBiOVO4.

PbBiOVO4 polymorphism.Figure optionsDownload as PowerPoint slide