Defect Structure of Lead Pyroniobates

Rick Ubic, Boise State University
J. C. Merry, Queen Mary, University of London
A. C. Leach, Queen Mary, University of London
I. M. Reaney, University of Sheffield

Abstract

The crystal structure of defect pyrochlores in the PbO - Nb₂O₅ system have been investigated by powder x-ray diffraction, electron diffraction, and high-resolution electron microscopy. Single-phase cubic pyrochlore was obtained for Pb_aNb₂O_5+n (n = 1.5); but for n > 1.5, discreet Pb-rich layers were observed in a manner similar to Ruddlesden Popper and Aurivillius phases. The appearance of these defect layers, which form on <111> planes of the parent pyrochlore, results in a lowering of the overall symmetry to trigonal.