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 (Na 0.5 Bi 0.5 )TiO 3 ‐BaTiO 3 ‐(K 0.5 Na 0.5 )NbO 3 single crystal with a large field induced strain of ≈0.9% and a giant piezoelectric coefficient d 33 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., R 3c and P 4mm) play an important role in achieving the ultrahigh piezoelectricity. Transmission electron microscopy and scan probe microscopy are employed to verify the weak‐polar ferroelectric R 3c and P 4bm 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.