Stabilization of a new δ′δ′ polymorph in P-substituted Pb2BiVO6: Single crystal structure of Pb2Bi(V0.84P0.16)O6 and conduction properties of related materials

The single crystal structure of a new polymorph δ′-Pb2Bi(V1-xPx)O6δ′-Pb2Bi(V1-xPx)O6 has been investigated; on heating, direct phase transitions α→β→δα→β→δ and α→δα→δ were identified in Pb2Bi(V1−xPx)O6 solid solutions for x⩾0.10x⩾0.10, thus avoiding the high-temperature form decomposition noted in the (δ-Pb2BiVO6δ-Pb2BiVO6) mother phase at 480 °C, to a mixture of PbBiVO5 and Pb4BiVO8 before recomposition at 650 °C. Under a slow cooling process, the δ‐Pb2Bi(V1-xPx)O6δ‐Pb2Bi(V1-xPx)O6 high-temperature phase transforms into a closely related δ′-Pb2Bi(V1-xPx)O6δ′-Pb2Bi(V1-xPx)O6 new polymorph, preserved at room temperature. The structure of δ′-Pb2Bi(V0.84P0.16)O6δ′-Pb2Bi(V0.84P0.16)O6 has been solved from a single crystal data in the orthorhombic system, Pbca   space group, with a=5.922(1)Å, b=18.395(5)Å, c=11.864(3)Å, Z=8Z=8, and compared to a previous description of δ-Pb2BiVO6δ-Pb2BiVO6 in Pmcn, with b   lattice constant halved. Complementary structural investigations of δ′-Pb2Bi(V0.75P0.25)O6δ′-Pb2Bi(V0.75P0.25)O6 powder sample by the Rietveld method, and TEM diffraction studies, confirmed the lattice and space group settings. The structural relationship between the αα, δδ and δ′δ′ forms is completed for Pb2Bi(V1−xPx)O6, and ionic conductivity versus temperature has been measured in the new phase as well as in its related solid solutions.

Projection along [100] of the structure δ′-Pb2Bi(V0.84P0.16)O6δ′-Pb2Bi(V0.84P0.16)O6.Figure optionsDownload as PowerPoint slide