Sintering behavior and microwave dielectric properties of Bi3(Nb1−xTax)O7 solid solutions

Solid solutions of Bi3(Nb1−xTax)O7 (x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h)−1 between 0 ≤ x ≤ 1 and Bi3(Nb1−xTax)O7 ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi3(Nb1−xTax)O7 ceramics increased from 8.2 to 9.1 g cm−3, microwave permittivity decreased from 95 to 65 while Qf values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τf from −113 ppm °C−1 of Bi3NbO7 to −70 ppm °C−1 of Bi3TaO7. Microwave permittivity, Qf values and τf values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi3(Nb1−xTax)O7 ceramics could be a good candidate for low temperature co-fired ceramics application.