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

Al2O3-TiO2 composite dielectric ceramics have been prepared by different sintering techniques including high-temperature, high-pressure sintering (2.5 GPa, T = 1000 degrees C) and conventional pressureless sintering (T = 1350 degrees C). Formation of the Al2TiO5 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 (0.895 Al2O3-0.105 TiO2) exhibited Q x f = 210 THz, epsilon' = 12.5 and tau(f) = +2.0 ppm K-1 at room temperature. As an evidence of an additional, low-frequency (possibly Debye-type), extrinsic contribution to the dielectric loss, the Q x f value gradually increased with frequency and reached a plateau of Q x f approximate to 340 THz at approximately 80 GHz. It is demonstrated that Al2O3-TiO2 composites have considerable potential as dielectric resonators in the output multiplexers of communication satellites. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.