MSO ₄ (M = Ca, Sr, Ba) microwave dielectric ceramics with low dielectric constant

Abstract

Abstract MSO 4 (M = Ca, Sr, Ba) ceramics with relative densities exceeding 96% were prepared by solid‐state sintering at low sintering temperatures of 625–875°C, and their structures and microwave dielectric properties at 10–19 GHz were characterized. MSO 4 ceramics crystallized in orthorhombic symmetry with the space groups of Amma for CaSO 4 and Pnma for SrSO 4 and BaSO 4 . The optimal microwave dielectric properties were obtained with ε r = 5.85, Qf = 57 000 GHz, τ f,W = −98.8 ppm/°C for CaSO 4 , ε r = 10.95, Qf = 15 500 GHz, τ f,W = 101.6 ppm/°C for SrSO 4 , and ε r = 9.42, Qf = 38 200 GHz, τ f,W = −4.7 ppm/°C for BaSO 4 . The increased ε r and τ f,W while decreased Qf value in the order of CaSO 4 , BaSO 4 , and SrSO 4 were attributed to the enhanced rattling effect of M 2+ . Besides, the temperature dependence of τ f was weak for CaSO 4 and BaSO 4 , whereas much stronger for SrSO 4 . As most low‐ ε r microwave dielectric ceramics are of large negative τ f , the near‐zero τ f of BaSO 4 and positive τ f of SrSO 4 are rare, indicating they are potential candidates for millimeter‐wave communication as a temperature‐stable dielectric ceramic and a compensator for tuning negative τ f to near‐zero, respectively.