Crystal structures and microwave dielectric properties of novel low-permittivity Ba1- x Sr x ZnSi3O8 ceramics

Ba_1-xSr_xZnSi₃O₈ (x = 0.2–1.0) microwave dielectric ceramics were synthesized using the solid-state method at the temperature from 1087 °C to 1150 °C for 3 h. All compositions showed a single phase for Ba_1-xSr_xZnSi₃O₈ when x increased from 0.2 to 1.0, and a phase transition from monoclinic to triclinic structure occurred between 0.8 and 1.0. The relative permittivity of Ba_1-xSr_xZnSi₃O₈ ceramics decreased from 6.57 to 6.12 when the Ba²⁺ ions substituted by Sr²⁺ ions. However, the quality factor initially decreased from 34,735 GHz (x = 0.2) to 28,986 GHz (x = 0.4) and subsequently increased monotonously. The variation in the temperature coefficient of resonant frequency showed an opposite, slightly changing trend compared with that of the quality factor. A novel single-phase SrZnSi₃O₈, which possesses good microwave dielectric properties of ε_r = 6.12, Q×f = 78,064 GHz, and τ_f = −33.2 ppm/°C, was obtained for the first time at the sintering temperature of 1150 °C.