Microstructures and dielectric properties of (1−x)SrTiO₃–xCa_0.61Nd_0.26TiO₃ ceramic system at microwave frequencies

(1−x)SrTiO₃–xCa_0.61Nd_0.26TiO₃ (0.6 ≤ x ≤ 0.9) ceramics are prepared through the conventional solid-state route. The XRD results suggest that a single CaTiO₃-like perovskite structure is formed in the range of 0.6 ≤ x ≤ 0.9. Microscopic surface textures and microwave dielectric properties have been investigated by scanning electron microscopy, thermal dilatometry and microwave resonant measurement at the frequency 2–4.2 GHz, respectively. As the x value increases from 0.6 to 0.9, the dielectric constant (ε _r ) decreases due to the smaller ionic polarizability of Ca_0.61Nd_0.26TiO₃ than that of SrTiO₃. The (1−x)SrTiO₃–xCa_0.61Nd_0.26TiO₃ (0.6 ≤ x ≤ 0.9) ceramics sintered at temperatures 1,350–1450 °C for 4 h are accompanied by a decrease in ε _r from 166.8 to 115.7 and a decrease in the temperature coefficient of resonant frequency from +499.6 to +276.8 ppm/ °C, while a increase in the product of dielectric Q value and resonant frequency (Q × f) from 4,945 GHz (at 2.44 GHz) to 11,850 GHz (at 2.87 GHz). The resultant dielectric properties have made (1−x)SrTiO₃–xCa_0.61Nd_0.26TiO₃ ceramics as very interesting materials for microwave communication and passive component applications.