MnO2 doping stabilized antiferroelectric P phase and underlying physical mechanism in NaNbO3-SrTiO3 lead-free ceramics

The incorporation of a few amount of MnO2 into 0.88NaNbO3-0.12SrTiO3 lead-free ceramics was found to effectively stabilize the antiferroelectric orthorhombic P phase before its transition into antiferroelectric orthorhombic R phase, consequently featuring completely reversible electric field-induced antiferroelectric-ferroelectric phase transition. Not only reproducible double polarization hysteresis loops but also repeated sprout-like strain-field curves ensure great application potentials in large-displacement lead-free actuators owing to both large repeatedly-utilized strains of ∼0.33% and low driving field of ∼11 kV/mm. Combined results of XPS, Raman spectroscopy and dielectric properties indicate that the stabilized antiferroelectric P phase was closely related to the reduced B-site cation polarizability and oxygen vacancy concentration, while a slight change in antiferrodistortive degree would discourage the P-R phase transition. These results indicate that ionic doping is an alternative method to alter the antiferroelectric P phase stability of NaNbO3-based lead-free ceramics by synergistically considering the influencing factors of phase and crystal structure stability.