Tuning the temperature coefficient of the resonant frequency of the AlPO₄-BPO₄-SiO₂ ternaries with TiO₂ addition and sintering atmosphere control

Microwave ceramics with low relative dielectric permittivities (epsilon(r)), high-quality factors (Qxf values), and near-zero temperature coefficients of resonant frequency (tau(f)) are strongly required for the 5 G and forthcoming 6 G wireless communication system. Effects of the TiO2 addition and atmosphere control on the microstructures and microwave dielectric properties of 0.05AlPO(4)-0.05BPO(4)-0.90SiO(2) (5A5B90S) and 0.45AlPO(4)-0.45BPO(4)-0.10SiO(2) (45A45B10S) ternaries were investigated in this paper to achieve the above objective. Adding TiO2 produced the TiP2O7 and/or (TiO)(2)P2O7 secondary phases in the 5A5B90S, and TiP2O7 in the 45A45B10S sintered bodies, respectively, which improved their sinterabilities. Near zero-tau(f) value (tau(f) similar to -2.0(8) ppm/degrees C) whilst retaining low epsilon(r) (similar to 4.97(7)) and high Qxf value (54,000 +/- 1619 GHz) could be attained for the 5A5B90S with the addition of 15 wt% TiO2. In contrast, both the Qxf and tau(f) values deteriorated with the addition of TiO2 for the 45A45B10S. Sintering in the B2O3 protection atmosphere helps suppress the formation of TiP2O7 and/or (TiO)(2)P2O7 secondary phases for both samples, specifically in the surface layer of the sample, which increased the tunability of tau(f) to be near zero. Combined good microwave dielectric properties with epsilon(r) similar to 4.47(6), Qxf similar to 48000 +/- 950 GHz, tau(f) similar to - 2.1(8) ppm/degrees C; epsilon(r) similar to 5.05(8), Qxf similar to 45,326 +/- 900 GHz, tau(f) similar to - 7.6 +/- 1.2 ppm/degrees C could be attained for the 5A5B90S + 10 wt% TiO2 and 45A45B10S + 15 wt% TiO2 ceramics, respectively by sintering in B2O3 protection atmosphere.