MSO4 (M = Ca, Sr, Ba) microwave dielectric ceramics with low dielectric constant

• Published in: Journal of the American Ceramic Society 2023-02, Vol.106 (2), p.1250-1259
• Main Authors: Jia, Ying Qiang, Luo, Wei Kun, Li, Lei, Wu, Shu Ya, Chen, Xiang Ming
• Format: Article
• Language: English
• Subjects: alkaline earth sulfides; Barite; Barium sulfate; Calcium; Ceramics; Compensators; Crystallization; Dielectric properties; Dielectric strength; low dielectric constant; microwave/millimeter‐wave dielectric ceramics; rattling effect; Sintering; Strontium; Strontium sulfate; temperature coefficient of resonant frequency; Temperature dependence
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.18862

MSO4 (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. MSO4 ceramics crystallized in orthorhombic symmetry with the space groups of Amma for CaSO4 and Pnma for SrSO4 and BaSO4. The optimal microwave dielectric properties were obtained with εr = 5.85, Qf = 57 000 GHz, τf,W = −98.8 ppm/°C for CaSO4, εr = 10.95, Qf = 15 500 GHz, τf,W = 101.6 ppm/°C for SrSO4, and εr = 9.42, Qf = 38 200 GHz, τf,W = −4.7 ppm/°C for BaSO4. The increased εr and τf,W while decreased Qf value in the order of CaSO4, BaSO4, and SrSO4 were attributed to the enhanced rattling effect of M2+. Besides, the temperature dependence of τf was weak for CaSO4 and BaSO4, whereas much stronger for SrSO4. As most low‐εr microwave dielectric ceramics are of large negative τf, the near‐zero τf of BaSO4 and positive τf of SrSO4 are rare, indicating they are potential candidates for millimeter‐wave communication as a temperature‐stable dielectric ceramic and a compensator for tuning negative τf to near‐zero, respectively.