Lead Doped Calcium Niobate-Tantalate Pyrochlores: Phase Structure and Dielectric Properties
The microwave properties of lead pyroniobates have been shown to be influenced by their crystal structures. The incorporation of PbO rich layers as the concentration of Pb increases enables these materials to attain high Qf but this is offset by poor εr and τf performance. Isovalent doping of Ta5+ ions on the niobium sites can reduce τf. In a similar previous study, calcium niobate-tantalate with zero τf was derived but both εr and Qf were lower than for the lead pyroniobates. The present work aims to build on these findings by preparing pyrochlore ceramics simultaneously doped on both A and B sites, to give minimal τf values and enhanced quality factors for medium permittivity applications. A single phase composition of (Ca1·4Pb0·6) (Nb0·5Ta1·5) O7 was prepared by mixing precalcined batches of Ca2(Nb0·5Ta1·5) O7 and Pb2(Nb0·5Ta1·5) O7 in the appropriate ratio. Pellets were sintered to high densities and their dielectric properties tested. Preliminary data suggest that compositions with greater lead content and higher A/B cation ratio should be pursued.
J. C. Merry, A. C. Leach, and Rick Ubic. "Lead Doped Calcium Niobate-Tantalate Pyrochlores: Phase Structure and Dielectric Properties" British Ceramic Transactions 101.4 (2002): 143-145.
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