Structure and Dielectric Properties of Lead Pyrochlores

Rick Ubic, Boise State University
Ian M. Reaney, The University of Sheffield

Abstract

This work investigates the structure and stability of the pyrochlore solid solution Pb_nNb₂O5+_n using a combination of high-resolution electron microscopy and electron diffraction. The microwave dielectric properties of the series 1.5 ≤n≤3.0 have been established, and the effect of the substitution of Ta⁵⁺ for Nb⁵⁺ on dielectric properties has also been investigated for n= 1.5 and 2.0. Single-phase cubic pyrochlore was obtained for n= 1.5. Compositions for which n > 1.5 showed discreet PbO-rich layers on {111}_cubic planes between alternating slabs of pyrochlore, similar in appearance to Ruddlesden–Popper phases. The occurrence of these layers results in a lowering of the overall symmetry to trigonal, and their presence was found to have a profound effect on the microwave dielectric properties.