The microwave dielectric properties of the series PbnNb2O5+n (1.3 ≤ n ≤ 3.0) have been established in this work. Single-phase cubic pyrochlore was obtained for n = 1.5. Compositions for which n > 1:5 showed discreet PbO-rich layers between alternating slabs of pyrochlore, similar in appearance to Ruddlesden–Popper phases. These layers have a profound effect on the microwave properties, with n = 2 yielding the lowest τf (814 ppm/ºC) in the series. Attempts were made to reduce τf further by both Mg- and Ta-doping. The properties of Mg-doped Pb1.5Nb2O6.5 were investigated for several concentrations of Mg (on the Nb site) up to Pb1.5(Mg0.24Nb1.76)O6.14, but none showed great promise. Isovalent doping with Ta, PbnTaxNb2-xO5+n, was much more successful. Both the n = 1.5 as well as the n = 2 compositions showed a marked decrease in τf with an increasing amount of Ta.
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