Crystalline structure and dielectric relaxor behavior of MnO2-modified 0.8BaTiO3-0.2BiScO3 ceramics for energy storage application

Based on the synergistic roles of defect dipoles and MnO₂ sintering aid, 0.8BaTiO₃-0.2BiScO₃ (BTBS_0.2) ceramics with and without 0.3 wt% MnO₂ were prepared by a solid-phase reaction route. The impacts of MnO₂ dopant and sintering conditions on the crystalline structure, micro-morphology, dielectric, and energy storage properties were investigated in detail. The X-ray diffraction (XRD) and Raman results demonstrate the coexistence of tetragonal (T) and pseudo-cubic (pC) phases. The increased pC phase content caused by MnO₂ modification is beneficial for the improvement of the relaxation degree. The O 1s fine spectra of X-ray photoelectron spectroscopy (XPS) confirms a remarkable increase in the concentration of oxygen vacancy due to the acceptor Mn dopant, indicating the valence changes of Mn ions from Mn⁴⁺ to Mn³⁺/Mn²⁺. The reduced dielectric loss is induced by the improved density and the pinning effect from the defect dipoles, thereby yielding a higher E_b. An optimal energy density of W_rec = 0.70 J/cm³ with a high energy efficiency of η = 95.8 % at 140 kV/cm was realized in the BTBS_0.2+Mn ceramic composition sintered at 1300 °C. Moreover, the ceramic also exhibits good temperature stability (30–120 °C). Therefore, the BTBS_0.2+Mn ceramics have a promising application prospect in the energy storage field.