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 Q(f) but this is offset by poor epsilon(r) and tau(f) performance. Isovalent doping of Ta5+ ions oil the niobium sites can reduce tau(f). In a similar previous study calcium niobate-tantalate with zero tau(f) was derived but both epsilon(r) and Q(f) ivere 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 tau(f) values and enhanced quality factors for medium permittivity applications. A single phase composition of (Ca1.4Pb0.6)(Nb0.5Ta1.5)O-7 was prepared by mixing precalcined batches of Ca-2(Nb0.5T1.5)O-7 and Pb-2(Nb0.5Ta1.5)O-7 in the appropriate ratio. Pellets ivere 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.