Ferroelectric materials reveal an ultra-high piezoelectric effect because of their spontaneous polarization and show high potential for applications. At present, the lead-free piezoelectric materials are in a great demand because of their environmentally friendly character, but their performance needs to be improved. Generally, in order to enhance the piezoelectric coefficients, researchers could rely on a phase boundary and/or to grow single crystals. Here, a Ta-doped (K, Na)NbO3 (KNN) single crystal with the orthorhombic–tetragonal (O–T) phase boundary is grown via the top-seed solution growth method. Excellent piezoelectric coefficients (d33 ≈ 560 pC/N via the Berlincourt method and d33* ≈ 1353 pm/V derived from strain-electric field loops) are achieved in a K0.40Na0.60Ta0.41Nb0.59O3 single crystal. What is more, with the electric field rising from 0.5 kV/cm to 4 kV/cm, the converse d33 and the strain hysteresis level improve from 580 pm/V to 640 pm/V and from 0.052 to 0.104, respectively. Our results clarify that the high d33 can be attributed to the high domain density and the labyrinthine-domain structure. In addition, the electric-field-induced phase transition is also observed, which is supposed to cause the high d33*. This work not only reports the ultra-high piezoresponse of the KNN-based single crystal but also provides strong evidence for its mesoscale origin.

中文翻译：

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钽掺杂铌酸钾钠单晶的超高压电响应

铁电材料由于其自发极化而显示出超高压压电效应，并显示出很高的应用潜力。目前，无铅压电材料由于其环保特性而需求量很大，但其性能有待提高。通常，为了提高压电系数，研究人员可以依靠相界和/或生长单晶。在这里，通过顶晶种溶液生长方法生长具有正交-四方 (O-T) 相界的 Ta 掺杂 (K, Na)NbO3 (KNN) 单晶。在 K0.40Na0.60Ta0.41Nb0.59O3 单晶中实现了出色的压电系数（d33 ≈ 560 pC/N，通过 Berlincourt 方法得出，d33* ≈ 1353 pm/V，源自应变电场回路）。更，随着电场从 0.5 kV/cm 上升到 4 kV/cm，逆向 d33 和应变滞后水平分别从 580 pm/V 提高到 640 pm/V 和从 0.052 提高到 0.104。我们的结果阐明，高 d33 可归因于高域密度和迷宫域结构。此外，还观察到电场引起的相变，这可能会导致高 d33*。这项工作不仅报告了基于 KNN 的单晶的超高压电响应，而且为其中尺度起源提供了强有力的证据。还观察到电场诱导的相变，这应该会导致高 d33*。这项工作不仅报告了基于 KNN 的单晶的超高压电响应，而且为其中尺度起源提供了强有力的证据。还观察到电场诱导的相变，这应该会导致高 d33*。这项工作不仅报告了基于 KNN 的单晶的超高压电响应，而且为其中尺度起源提供了强有力的证据。