Development of Al2O3–TiO2Al2O3–TiO2 composite ceramics for high-power millimeter-wave applications

Al2O3–TiO2Al2O3–TiO2 composite dielectric ceramics have been prepared by different sintering techniques including high-temperature, high-pressure sintering (2.5 GPa, T = 1000 °C) and conventional pressureless sintering (T = 1350 °C). Formation of the Al2TiO5Al2TiO5 secondary phase has been completely suppressed by optimization of the sintering and annealing temperatures. Dielectric properties were measured in the 10–11 GHz range using the cylindrical resonant cavity technique and in the 40–92 GHz range using the open resonator whispering gallery mode technique. At 10 GHz, the optimized composite material (0.895Al2O3–0.105TiO2) exhibited Q×f=210THz,ε′=12.5 and τf=+2.0ppmK-1 at room temperature. As an evidence of an additional, low-frequency (possibly Debye-type), extrinsic contribution to the dielectric loss, the Q × f value gradually increased with frequency and reached a plateau of Q × f  ≈340THz at approximately 80 GHz. It is demonstrated that Al2O3–TiO2Al2O3–TiO2 composites have considerable potential as dielectric resonators in the output multiplexers of communication satellites.