Evolution of loss tangent with structural ordering of the perovskite-type Ba₃CaNb₂O₉ ceramics

In this paper, we investigate the microwave dielectric properties considering the de-gree of disorder, which plays a fundamental role in the values of dielectric loss, for the perovskite-type Ba₃CaNb₂O₉ ceramics. Dense ceramics were prepared by con-ventional method in solid state reactions and their dielectric properties were then ob-tained as a function of sintering time. The coexistence of domains in the 1:1 (cubic) and the 1:2 (trigonal) ordering types in all samples was realized. Specifically, the in-crease of sintering time tends to reduce the domains 1:1, raising the unloaded quality factor (Q_u). The domain (1:1) acts as a lattice vibration damping, thus increasing the dielectric loss at resonance. The best performance was recorded in sintered ceramic at 1500° C for 32 h: ε_r = 43 (relative permittivity), Q_u × f_R = 15,752 GHz (resonant frequency f_R = 7.76 GHz) and τ_f = 278 ppm/deg C (coefficient of resonant frequency variation with temperature). (author)