Dielectric properties and applications of low loss (1 - x)(Mg_0.95Co_0.05)TiO₃-xCa_0.8Sm_0.4/3TiO₃ ceramic system at microwave frequency

In this paper, the microstructures and microwave dielectric properties of the (1 - x)(Mg_0.95Co_0.05)TiO₃-xCa_0.8Sm_0.4/3TiO₃ (x = 0.05-0.2) ceramic system were investigated. Ca_0.61Sm_0.78/3TiO₃ increased the dielectric constant (ε_r), reduced the quality factor (Q × f value) and also compensated the temperature coefficient of resonant frequency (τ_f) of (Mg_0.95Co_0.05)TiO₃. The microstructures of (1 - x)(Mg_0.95Co_0.05)TiO₃-xCa_0.8Sm_0.4/3TiO₃ ceramics were characterized by X-ray diffraction patterns, scanning electron microscope (SEM). The existing areas of different compositions in the ceramics were observed by means of energy dispersive spectroscopy (EDS), which revealed that Ca_0.8Sm_0.4/3TiO₃ as minor phase co-existed with (Mg_0.95Co_0.05)TiO₃. The existing Ca_0.8Sm_0.4/3TiO₃ phase can inhibit the grain growth of the main (Mg_0.95Co_0.05)TiO₃ phase. A dielectric constant (ε_r) of 22.5, a Q × f value of 108,000 (at 8 GHz ) and a τ_f value of -8 ppm/°C were obtained for 0.9(Mg_0.95Co_0.05)TiO₃-0.1Ca_0.8Sm_0.4/3TiO₃ ceramic sintered at 1275 °C for 4 h. Moreover, an ISM band parallel-coupled line band-pass filter with a central frequency of 5.8 GHz was also designed and fabricated using the proposed material as substrate to study its performance. It also showed a substantial reduction in both insertion loss and size in comparison with other dielectrics FR4 and alumina.