Giant Electrostrain in Lead-Free BiFeO₃-BaTiO₃ Ceramics via High-Entropy Design

Piezoelectric actuators, enabling the conversion of electrical energy into mechanical strain, are pivotal in various electromechanical applications. The morphotropic phase boundary (MPB) approach has been widely used to enhance the electrostrain performance of piezoelectrics. It remains to be explored alternative frameworks beyond the conventional MPB method. Here, a high-entropy strategy is used to enhance the electromechanical response of ferroelectric materials with pristine composition near MPB. By incorporating chemical disorders through the high-entropy strategy, atomic disordered arrangements and severe lattice distortions are induced in the BiFeO₃-BaTiO₃ (BF-BT) system, thus promoting the formation of nanopolar regions and nanodomain structures, facilitating a more flattened energy profile and mutual phase transformation under an electric field and improving the electromechanical response activity of lattices. As a result, high-entropy BF-BT-based polycrystalline ceramics exhibit an ultrahigh electromechanical response with a giant unipolar electrostrain of 1.23% at 80 kV cm^-1 with fatigue-free resistance to cyclic electric fields. The effective converse piezoelectric coefficient (d₃₃*) reaches 1537 pm V^-1, surpassing most lead-free piezoelectrics. Our work highlights the potential of high-entropy design in ferroelectric materials as high-performance piezoelectric actuators.