Large Piezoelectricity in Ternary Lead‐Free Single Crystals

Since industry‐standard piezoelectric materials, such as lead zirconium titanate ceramics, contain toxic lead, a rapid surge in research on lead‐free piezoelectric materials is occurring due to concerns over environmental safety and human health. A ternary lead‐free (Na0.5Bi0.5)TiO3‐BaTiO3‐(K0.5Na0.5)NbO3 single crystal with a large field induced strain of ≈0.9% and a giant piezoelectric coefficient d33 of 840 pC N−1 at room temperature is reported. It is revealed that the electric‐field‐induced phase transition and phase boundary between energetically comparable polar states (i.e., R3c and P4mm) play an important role in achieving the ultrahigh piezoelectricity. Transmission electron microscopy and scan probe microscopy are employed to verify the weak‐polar ferroelectric R3c and P4bm structure in the ground state. These unprecedentedly high piezoelectric properties make lead‐free ternary single crystals a leading candidate for piezoelectric‐based device applications, especially toward the era of smart homes and implantable medical devices.