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 T_C variation (13 °C) and excellent piezoelectric and dielectric response (d₃₃ = 373 pC/N and ${\epsilon }_{33}^T$ = 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 ($d_{33}^{\ast }$), dielectric (${\epsilon }_{33}^{T\ast }$), elastic ($s_{33}^{E\ast }$)and electromechanical coupling ($k_{33}^{\ast }$) 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.

钙钛矿K(Ta,Nb)O ₃ (KTN)单晶以其优异的电光性能和优异的压电响应引起了人们的极大兴趣。然而，对于 Nb 和 Ta 之间巨大的偏析差异，成分均匀的 KTN 单晶的生长一直是一个巨大的挑战。在这项工作中，我们提出了一种热场优化策略来解决这一挑战。均质 Sn 掺杂 KTN (Sn:KTN) 单晶，具有显着降低的成分梯度（0.003 mol/mm，是其他 KTN 系统的 1/4–1/8）、最小的T _C变化（13 °C）和出色的压电和介电响应( d ₃₃  = 373 pC/N 和${\epsilon }_{33}^{吨}$ = 5206) 已成功实现。我们发现 Sn:KTN 的功能特性受到近室温四方-立方相变的极大影响。从本征方面来看，纵向晶格变形变得更加容易，导致最大压电（$d_{33}^{*}$), 电介质 (${\epsilon }_{33}^{吨*}$）， 松紧带 （$s_{33}^{乙*}$) 和机电耦合 (${ķ}_{33}^{*}$) 沿极方向的系数 [001] _C . 从外在方面来看，畴壁密度和畴壁迁移率都得到了极大的改善，从而减少了晶格畸变，这也对功能特性有很大贡献。这项工作为设计和生长高质量晶体提供了一条简单实用的途径，更重要的是，揭示了相变/功能特性边界的基本机制。