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 xSrTiO(3)-(1-x)Ca(Mg1/3Nb2/3)O-3 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 epsilon(r)similar to 205, Q x f value similar to 4200 GHz and a large positive tau(f) value similar to 1700 ppm/degrees C. Ca (Mg1/3Nb2/3)O-3 possesses high dielectric constant (epsilon(r) similar to 28), high quality factor (Q x f value similar to 58,000 at 7 GHz) and negative tau(f) value (-48 ppm/degrees C). As the x value varies from 0.2 to 0.8, the xSrTiO(3)-(1-x)Ca(Mg1/3Nb2/3)O-3 system has the dielectric properties as follows: 40 <epsilon(r)< 123, 4600 < Q x f < 33,400 and -23 <tau(f)< 600. A new microwave dielectric material, 0.3SrTiO(3)-0.7Ca(Mg1/3Nb2/3)O-3, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant epsilon(r) similar to 46, a Q x f value similar to 29,300 GHz(at 6.8 GHz) and a tau(f) value similar to -2 ppm/degrees C. A near-zero tau(f) value can be achieved by adjusting the x value of xSrTiO(3)-(1-x)Ca(Mg1/3Nb2/3)O-3 ceramics. (c) 2005 Elsevier B.V. All rights reserved.