Properties of the microwave dielectric phase Ba6-3XNd8+2XTi18O54

The Ba6-3xRE8+2xTi18O54 (RE = rare-earth element) solid solution has been w ell established as a useful microwave resonator material due to its high di electric constant (epsilon(r)),low loss (tan delta = 1/Q), and tunable temp erature coefficient of resonant frequency (tau(f)) Ceramics of this phase ( RE = Nd) have been processed in this study by a mixed-oxide route, and the variation in properties caused by divalent and tetravalent doping was inves tigated. Dielectric properties have been measured for single-phase pellets with the stoichiometries x = 0.25, 0.50, and 0.75. As the value of x increa sed, Q was found to increase significantly, and both epsilon(r) and tau(f) decreased, Various dopants, including Ca, Sr, Pb, Zr, and Hf, were used in the n = 0.75 composition to tune electrical properties, with varying degree s of success, Most doped samples were multiphase, Ca- and Sr- doping, while raising epsilon(r) of the ceramic, resulted in very poor Q's and unaccepta bly high values of tau(f). Zr- and Hf-doping, on the other hand, caused a m odest reduction in tau(f) but produced drastic reductions in Q and epsilon( r). Only ph-doping was found to usefully reduce tf whilst leaving both epsi lon(r), and Q at reasonable levels. The composition which exhibited the bes t properties was (Ba0.875Pb0.125)(3.75)Nd9.5Ti18O54, for Which epsilon(r) = 72, Q = 1000 (at 6.1 GHz), and tau(f) = 8-11 ppm/degrees C.