Effects of Mn doping and sintering condition on the microstructure, dielectric, and energy storage properties of Ba0.8Sr0.2TiO3 ceramics

Mn 2+ ion, as an acceptor dopant, is usually employed to optimize the microstructures and electrical properties of BaTiO 3 -based lead-free ceramic systems. In this work, Ba 0.8 Sr 0.2 (Ti 1 −  x Mn x )O 3 (BSTM, x  = 0-0.005 mol) ceramics were synthesized using the solid-state sintering technique. The effects of Mn 2+ doping content and sintering condition on the microstructure, dielectric, and energy storage properties of BSTM ceramics were studied and discussed. Compared with undoped samples, the Mn doping with a low concentration of x  < 0.005 mol can effectively reduce the average grain size of BSTM ceramics when sintered at 1300 °C/3 h. It is also found that Mn 2+ doping can decrease the dielectric loss and enhance remarkably the electrical strength ( E BDS ). This is because Mn replaces B-site Ti 4+ ions, thus generating oxygen vacancies as well as defect dipoles \([Mn_{{Ti}}^{{nn}} - V_{O}^{{ \cdot \cdot }} ]\) . With an increase in Mn 2+ doping content, more oxygen vacancies are produced to modify the microstructure and electrical properties. However, either elevated sintering temperature (e.g., 1325 °C) or prolonged sintering time (e.g., 1275 °C/5 h) can induce a rapid growth of grain size, leading to the weakened relaxation characteristics and the valence transformation from Mn 2+ to Mn 3+ / Mn 4+ , but the energy efficiency of BSTM ceramics is enhanced due to the thin P– E ferroelectric loops. The significant impacts of Mn 2+ doping and sintering conditions on the morphology structure and electrical properties need to be considered for the better optimization of energy storage properties of relaxor ferroelectric ceramics.