Tetragonal (K, Na)NbO₃ based lead-free single crystal: Growth, full tensor properties, and their orientation dependence

A Li and Ta modified (K, Na)NbO₃ lead-free single crystal with a large size (13 × 10 × 20 mm³) has been grown by using the top-seeded solution growth method. The large size allows us to carry out an extensive study on this tetragonal crystal. We have measured a complete set of elastic, dielectric, and piezoelectric constants for the [001]_C poled crystal with the single domain state. The crystal exhibits high shear piezoelectricity with d₁₅ = 518 pC/N and k₁₅ = 0.733, showing excellent potential in shear electro-sonic energy transformation devices. It is found that the high shear piezoelectricity originates from the vicinity of orthorhombic-tetragonal phase transition, which favors polarization rotation greatly. The orientation dependence of longitudinal dielectric, piezoelectric, and elastic constants and electromechanical coupling factor in the 3-dimentional space were calculated based on the single domain dataset. We believe that this work is of great importance for both fundamental studies and device designs for lead-free materials.