Multifunctional BaTiO3-Based Relaxor Ferroelectrics toward Excellent Energy Storage Performance and Electrostrictive Strain Benefiting from Crossover Region

Lead-free relaxor ferroelectrics (RFEs) exhibit a broader variety of phenomena in comparison with the "canonical" lead-containing compositions, rendering them attractive for newly multifunctional materials with low-cost and eco-friendly processing. Here, guided by the characteristics of relaxor ferroelectrics, lead-free (1 - x)BaTiO3-xKNbO3 systems are conceived and optimized to construct a special crossover region, which brings multiple benefits including tiny hysteresis loss while pursuing high maximum polarization, and large electrostrictive strain with low hysteresis, targeting multifunctional applications of energy storage capacitors, and electrostrictive actuators. We obtained fine-grained 0.96BaTiO3-0.04KNbO3 ceramic with a crossover region where nanodomains and nanosized polar regions with highly dynamic coexist, achieving a large recoverable energy density of 2.03 J/cm3 (300 kV/cm) simultaneously with sky-high charge-discharge efficiency of 94.5%, where low-cost production and environmental issues are warranted. By utilizing the crossover region, superior temperature-stable energy storage capacity (without a drop from 20 to 130 °C) guarantees the practical use. Meanwhile, this strategy favors large electrostrictive strain (0.146%) with ultralow hysteresis in 0.96BT-0.04KN at 80 kV/cm, which is suitable for electrostrictive actuators. It is expected that this strategy will stimulate future studies on lead-free multifunctional RFEs toward energy storage capacitors or electrostrictive actuators with low-cost and environmental compatibility.