(Sr1‐xCax)2TiO4 microwave dielectric ceramics with R‐P structure (x = 0~0.15)

Abstract

Abstract(Sr1‐xCax)2TiO4 ceramics (0 ≤ x ≤ 0.15) were synthesized by a standard solid state reaction route. Tetragonal Ruddlesden‐Popper (R‐P) solid solutions (Sr1‐xCax)2TiO4 with space group I4/mmm were obtained in the composition range of x = 0~0.15, while Sr3Ti2O7 has been observed as secondary phase in x ≤ 0.10. In the present ceramics, both the dielectric constant ɛr and temperature coefficient of resonant frequency τf decreased at first and turned to increase again with increasing x, while the quality factor Qf decreased slightly at first and turned to decrease sharply after x = 0.1. The improved microwave dielectric properties with the best combination were obtained in (Sr1‐xCax)2TiO4 ceramics at x = 0.075: ɛr = 39.3, Qf = 93 550 GHz, τf = 119 ppm/°C The obvious improvement was achieved in temperature coefficient of resonant frequency (from 140 to 119 ppm/°C) with Ca2+‐substitution for Sr2+ in Sr2TiO4 ceramics due to the increased B‐site bond valance.