Superior Electrostrictive Effect in Relaxor Potassium Sodium Niobate Based Ferroelectrics

Electromechanical actuators with toxic lead-based electrostrictive materials dominate the market of high-precision electronics devices, so one of urgent aims becomes how to explore the new generation of ecofriendly electrostrictive materials with superior electrostriction behaviors. Herein, a strategy of modifying the active space for the B-site in lead-free relaxor ferroelectrics arouses the potential capacity of electrostriction, including K_0.5Na_0.5NbO₃ (KNN). Through co-doping of Bi³⁺ and Ni²⁺, typical relaxor ferroelectrics (1 - x)K_0.5Na_0.5NbO₃-xBiNi_2/3Nb_1/3O₃ (KNN-xBNN, 0.03 ≤ x ≤ 0.07) are constructed because of the incorporation of dopants ions on the A- or B-site promotes structural disorder. Importantly, a limited active space for the B-site is obtained owing to the contracted oxygen-octahedron with smaller A-site dopants induced by lattice distortion. Benefiting from the design strategy, a remarkable enhancement of electrostrictive coefficient Q₃₃ of ∼0.0456 m⁴/C² is achieved, which is higher than those of KNN-based materials and also twice as large as those of lead based materials. The Q₃₃ also exhibits a relatively good electric field and is temperature-independent. A giant Q₃₃ of 0.0512 m⁴/C² is gained at a high frequency of 100 Hz, meeting the requirement of some commercial actuators for fuel injectors. Such a strategy may help us design high-performance electrostrictive materials.