Low-temperature sintering and dielectric properties of Ag(Nb,Ta)O₃ composite ceramics

The sintering behavior and dielectric properties of perovskite Ag(Nb_1-xTa_x)O₃ (O < × < 1) solid solutions and two-phase composite assemblages were explored. A small amount of CuO (1 wt%) was used for liquid-phase sintering and led to high densification at temperatures <950°C. The temperature coefficient of capacitance, TCC, was adjusted by varying the Nb:Ta ratio within the solid-solution series and by creating composite microstructures. Two-phase assemblages consisting of Ag(Nb_3/4Ta_1/4)O₃ and Ag(Nb_1/4Ta_3/4)O₃ were synthesized to achieve a temperature-stable dielectric material for high-frequency applications. The composite dielectric with CuO addition had an average dielectric constant of 390 and a Q X f factor of 410 GHz at 2 GHz, with a stable TCC (0 to -180 ppm/°C) in the temperature range from -20° to +60°C. In addition, process compatibility with a silver conductor was confirmed by high-frequency ring-resonator measurements and microstructural characterization. The Ag(Nb_1-xTa_x)O₃ solid solutions and composites are promising candidates as embedded capacitors for radio-frequency/microwave applications.