Abstract
The PbO–Nb 2 O 5 phase diagram has been investigated, using electron diffraction and high resolution electron microscopy (HREM), for [Pb]/[Nb] ratios between 1 and 1.25. Apart from the basic pyrochlore structure, different long period superstructures, forming a homologous series Pb 2 n +1 Nb 2 n −1 O 7 n −1 based on the pyrochlore structure have been found. Members with n = 5, 7, 9, 11 have been observed and their structure determined based on electron diffraction and HREM. Image simulations allow studying the influence of cation and oxygen vacancies in the basic structure. Ordering of oxygen vacancies could be detected while no cation vacancies are observed. Deviations from the perfect structure and ordered stacking defects are discussed.
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