Microstructure and dielectric properties of medium-entropy MeTiO₃ (Me = Ca, Sr, Ba, Mg) ceramics with A-site cation disorder

The rapid development of pulsed power technologies has imposed stringent requirements on high-performance dielectric materials. In this study, medium-entropy perovskite ceramics MeTiO₃ (Me = Ca, Sr, Ba, Mg) were designed and synthesized via a conventional solid-state reaction approach. The effects of the A-site cation on the microstructure and dielectric performance were investigated. The results showed that low A-site size mismatch (e.g., (Ca_1/3Sr_1/3Ba_1/3)TiO₃) yielded single-phase cubic perovskites, whereas higher mismatch promoted multiphase structures. Raman spectroscopy confirmed the presence of significant lattice distortion, and the incorporation of Mg²⁺ enhanced the densification process and inhibited abnormal grain growth. Notably, in the (Ca_1/3Ba_1/3Mg_1/3)TiO₃(CBM) composition, the coexistence of (CaMg)TiO₃ and (BaMg)TiO₃ phases enhances interfacial effects. The partial incorporation of Mg²⁺ into A-site and the formation of Mg-containing secondary phases induce ionic radius mismatch, lattice distortion, and the formation of defect dipoles, leading to a synergistic “lattice distortion–interfacial polarization” effect. Consequently, the CBM ceramics exhibit an ultralow dielectric loss (< 10^–3), a high breakdown strength of 240 kV·cm⁻¹, and excellent temperature stability, with the temperature coefficient of capacitance (TCC_25℃) varying by less than 5% over the range of − 70–150 ℃. These results highlight the medium-entropy perovskite ceramics as promising candidates for pulsed power devices and next-generation advanced dielectric capacitors.