Effect of divalent dopants on properties of Ba_3.75Nd_9.5Ti₁₈O₅₄ microwave dielectric resonators

Pellets in the ternary solid-solution Ba_6-3xNd_8+2xTi₁₈O₅₄ (x = 0.75) have been processed to near theoretical density by mixed-oxide synthesis, and their dielectric properties determined to be ε_r≈89, Q_f>10,000, and τ_f≈+60 ppm/°C at microwave frequencies. Similar ceramics with Ca, Sr, and Pb partially substituted for Ba were also processed and analyzed. Both Ca and Sr were found to increase ε_r to 100-105 but significantly lower Q_f and inflate τ_f. While Pb substitution also lowered Q_f, it had no significant effect on ε_r and beneficially suppressed τ_f to values from -16 to +8 ppm/°C, tunable with Pb content, strongly suggesting that these materials may be useful for commercial applications.