CaTiO3–Sm0.9Nd0.1AlO3 ceramics with a moderate dielectric constant and a high quality factor prepared by sol–gel auto combustion method

Abstract

CaTiO3–LnAlO3 (Ln = La, Nd, Sm) is a perovskite-type microwave material system characterized by a moderate dielectric constant εr, a high quality factor Q × f, and a small temperature coefficient of resonant frequency τf, making this system promising for microwave devices. However, its high synthesis temperature and sintering temperature limit its industrial applications. In our work, single phase 0.7CaTiO3–0.3Sm0.9Nd0.1AlO3 (7CT–3SNA) was synthesized via the sol–gel auto combustion method using citric acid as fuel at a relatively low temperature. After being calcined at 600 °C for 2 h, well-crystallized 7CT–3SNA powders with 30–50 nm average particle size were achieved, suggesting good sintering activity. The new and narrow order band at about 800 cm−1 in the Raman spectra indicates a high ordering degree in the B site of 7CT–3SNA solid solution. Compared with the solid–state reaction method and co-precipitation method, the 0.7CT–0.3SNA ceramics fabricated by the current method possess a much lower calcination temperature, a similar εr value, and an improved Q × f value. The optimum microwave dielectric properties of εr = 43.54, Q × f = 54375 GHz, and τf = −6.3 × 10−6/°C are obtained for the CTSA ceramics derived from the sol–gel auto combustion process. Therefore, the 7CT–3SNA ceramics prepared in this study are potential dielectric materials for microwave applications, indicating that the sol–gel auto combustion method is a good alternative strategy for the fabrication of CaTiO3–LnAlO3 ceramics.