Homogenous Sn-doped K(Ta,Nb)O3 single crystals and its high piezoelectric response

Perovskite K(Ta,Nb)O3 (KTN) single crystal has drawn great interests for its outstanding electro-optic performance and excellent piezoelectric response. However, growth of compositionally uniform KTN single crystals has always been a great challenge for the great segregation difference between Nb and Ta. In this work, we propose a thermal field optimization strategy to resolve this challenge. Homogenous Sn doped KTN (Sn:KTN) single crystal with significantly reduced composition gradient (0.003 mol/mm, 1/4–1/8 of other KTN system), minimal TC variation (13 °C) and excellent piezoelectric and dielectric response (d33 = 373 pC/N and ε33T = 5206) has been successfully achieved. We found that the functional properties of Sn:KTN were greatly affected by the near-room temperature tetragonal-cubic phase transition. From the intrinsic aspect, longitudinal lattice deformation becomes much easier, resulting in maximum piezoelectric (d33∗), dielectric (ε33T∗), elastic (s33E∗)and electromechanical coupling (k33∗) coefficients along polar direction [001]C. From the extrinsic aspect, both domain wall density and domain wall mobility are greatly improved for the reduced lattice distortion, which also contribute a lot to the functional properties. This work provides a simple and practical route for designing and growing high quality crystals, and more importantly, reveals the fundamental mechanism of the phase transitions/boundaries on the functional properties.