(Ba 1-y Pb y ) 3·75 Nd 9·5 Ti 18 O 54 and (Ba 1-y Sr y ) 3·75 Nd 9·5 Ti 18 O 54 microwave dielectric ceramics: Effect of Pb and Sr substitution on dielectric properties

Two series of substitutionally doped ceramics, (Ba_1-yPb_y)_3·75Nd_9·5Ti₁₈O₅₄ and (Ba_1-ySr_y) _3·75Nd_9·5 Ti₁₈O₅₄, with y = 0·02, 0·05, 0·1, 0·2, and 0·5, were prepared by the mixed oxide route to examine the effect of substituting barium with lead or strontium. Samples were sintered at temperatures in the range 1350 to 1500°C, yielding products with densities typically 95% of theoretical. It was found that in each series up to approx imately 20% of the barium could be substituted before the solubility limit was reached. The relative permittivity ϵ_r was found to be approximately 80 for all compositions, and was almost independent of changes in the lead or strontium content. The product of the dielectric Q value and resonant frequency Q × f₀ reached a peak of 9700 in the lead doped system with y = 0·02. In the strontium doped series a peak Q × f₀ value of 11 000 was achieved, also at y = 0·02. At higher levels of strontium substitution the temperature coefficient of permittivity Tϵ_r became increasingly negative. In the Ba-Pb series, Tϵ_r changed from -40 to +52 ppm K^-1 for substitutions in the range y = 0·05 to 0·20, thus providing a means of achieving temperature stable dielectric properties in BaO-Nd₂O₃-TiO₂ based ceramics.