New dielectric materials of xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 ceramic system at microwave frequency

The crystal structures and the microwave dielectric properties of the xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 perovskite ceramic system have been investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. SrTiO3 has dielectric properties of dielectric constant εr ∼ 205, Q × f value ∼ 4200 GHz and a large positive τf value ∼ 1700 ppm/°C. Ca(Mg1/3Nb2/3)O3 possesses high dielectric constant (εr ∼ 28), high quality factor (Q × f value ∼ 58,000 at 7 GHz) and negative τf value (− 48 ppm/°C). As the x value varies from 0.2 to 0.8, the xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 system has the dielectric properties as follows: 40 < εr < 123, 4600 < Q × f < 33,400 and − 23 < τf < 600. A new microwave dielectric material, 0.3SrTiO3–0.7Ca(Mg1/3Nb2/3)O3, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant εr ∼ 46, a Q × f value ∼ 29,300 GHz (at 6.8 GHz) and a τf value ∼− 2 ppm/°C. A near-zero τf value can be achieved by adjusting the x value of xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 ceramics.