Ultra-high electrostrain in flux-grown (Bi0.5Na0.5)TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 single crystals around the nonergodic/ergodic crossover region

In this study, we successfully grew large-sized single crystals (12 × 11 × 8 mm³) of 0.91Bi0.5Na0.5TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 (BNT-6BT-3KNN) with a <100>c orientation using the flux growth method. This marks the first instance of achieving such crystals. The single crystals display double hysteresis loops, featuring a maximum polarization of ∼64.6 μC/cm2. Capitalizing on the nonergodic/ergodic boundary, the single crystals exhibit a substantial strain (Sm) of 0.91% at the maximum electric field of 20 kV/cm and an exceptionally high inverse piezoelectric coefficient d33* of 4550 pm/V. The creation of long-range domains from needle-like nanodomains and polar-nano regions under the application of an electric field was confirmed through bright-field transmission electron microscopy and piezoresponse force microscopy analyses. The phase diagram for BNT-6BT-3KNN single crystals was constructed by analyzing the temperature dependence of dielectric, ferroelectric, and electrostrain behaviors.