Microwave properties of doped lead pyroniobate

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/°C) 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.