Microstructural and dielectric properties of Ba0.45Mg0.05Sr0.5-x CaxTiO3 high entropy ceramics

Ba0.45Mg0.05Sr0.5-xCaxTiO3 (BMSCT) high entropy ceramics were prepared using a solid-state reaction process sintered at temperatures ranging from 1250 °C to 1400 °C. A change in Ca content significantly affects the crystalline phase and dielectric properties of the BMSCT ceramics. High resolution TEM observations and the analysis of respective images reveal a large number of intragranular on the nanoscale that are massively disordered and disturbed on the atomic level. The influence of Mg doping, resulting in a shift of the Curie point to −50 °C. For Ca-substitution (up to 10 at.%), a broad phase transition is observed in the BMSCT, and the Curie point is −30 °C. Comparing the dielectric constant at 1 MHz and 1 GHz, the permittivity of the BMSCT-9182 is only slightly inferior to the on at low frequency ~6%, but the one for BST is drastically decreased ~70% at microwave frequencies.