Structural mechanism behind piezoelectric enhancement in off-stoichiometric Na0.5Bi0.5TiO3 based lead-free piezoceramics
Structural mechanism behind piezoelectric enhancement in off-stoichiometric Na0.5Bi0.5TiO3 based lead-free piezoceramics
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DOI：
10.1016/j.actamat.2018.11.015
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发表时间：
2019-02
期刊：
影响因子：
9.4
通讯作者：
A. Mishra;D. Khatua;Arnab De;B. Majumdar;T. Frömling;R. Ranjan
中科院分区：
文献类型：
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作者：
A. Mishra;D. Khatua;Arnab De;B. Majumdar;T. Frömling;R. Ranjan
虽然在过去的研究表明，某些种类的非化学计量比提高无铅压电陶瓷Na0.5Bi0.5TiO3（NBT）的压电响应，有一个缺乏清晰的机制与这个有趣的现象从基本结构的角度来看。在本文中，我们已经全面研究了这个问题，并成功地建立了一个相互之间的对应关系的非化学计量比，晶粒尺寸，晶体结构，介电和压电性能在Na0.5Bi0.5TiO3（NBT）。在根据标称公式即Na 0.5 + xBi 0.5TiO 3合成的四种不同类型的非化学计量样品中，（Na过量Na系列），Na0.5-xBi0.5TiO3（缺Na Na系列），Na0.5Bi0.5+ xTiO 3（Bi过量Bi系列）和Na0.5Bi0.5-xTiO 3（缺Bi Bi系列）中，x = 0.04的缺Na系列获得了最好的压电响应（d33 × 100 pC/N）。我们成功地建立了非化学计量和压电性之间的结构联系，这一系列通过检查在其极化状态的标本的结构状态。我们发现，非化学计量的组合物表现出较高的压电响应包含较高的分数的无序铁电相共存的场稳定的长程铁电（R3 C）秩序。超过临界非化学计量比（x > 0.04），结构无序的优势崩溃系统的压电响应。我们还表明，可以实现的非化学计量比也可以通过减少化学计量NBT的晶粒尺寸。我们的研究结果表明，增强的压电响应的非化学计量组合物是由于其减小的晶粒尺寸相比，化学计量组合物，和缺陷物种的性质具有次要的作用，如果有的话。我们发现同样的现象/机制是在非化学计量准同型相界组成0.94Na0.5Bi0.5TiO3-0.06BaTiO3（NBT-6 BT）。虽然我们的实验证实了生存的结构异质性（极化后）作为一个重要的贡献因素，提高了NBT基无铅压电陶瓷的压电响应的作用，我们还使用介电色散作为一种工具，以显示非化学计量的组合物表现出最高的压电响应的特点是由极化场的无序相的最大抑制。
While studies in the past have shown that certain kinds of off-stoichiometry enhance the piezoelectric response of the lead-free piezoceramic Na0.5Bi0.5TiO3(NBT), there is a lack of clarity regarding the mechanism associated with this interesting phenomenon from the fundamental structural perspective. In this paper, we have investigated this issue comprehensively and succeeded in establishing a mutual correspondence between off-stoichiometry, grain size, crystal structure, dielectric and piezoelectric properties in Na0.5Bi0.5TiO3(NBT). Of the four different types of off-stoichiometric samples synthesized as per nominal formulae namely Na0.5+xBi0.5TiO3(Na-excess Na-series), Na0.5-xBi0.5TiO3(Na-deficient Na-series), Na0.5Bi0.5+xTiO3(Bi-excess Bi-series), and Na0.5Bi0.5-xTiO3(Bi-deficient Bi-series), the best piezoelectric response (d33∼ 100pC/N) was obtained in the Na-deficient series with x = 0.04. We succeeded in establishing the structural link between off-stoichiometry and piezoelectricity of this series by examining the structural state of the specimens in their poled state. We show that the off-stoichiometric compositions exhibiting higher piezoelectric response contain a higher fraction of the disordered ferroelectric phase coexisting with the field stabilized long-range ferroelectric (R3c) order. Beyond the critical off-stoichiometry (x > 0.04), the dominance of the structural disorder collapses the piezoelectric response of the system. We also show that what can be achieved by off-stoichiometry can as well be achieved by reducing the grain size of stoichiometric NBT. Our results suggest that the enhanced piezoelectric response of the off-stoichiometric compositions is due to their reduced grain size as compared to the stoichiometric composition, and that the nature of the defect species has a secondary role, if any. We found the same phenomenon/mechanism to be operative in the off-stoichiometric morphotropic phase boundary composition 0.94Na0.5Bi0.5TiO3-0.06BaTiO3(NBT-6BT). While our experiments confirm the role of the surviving structural heterogeneity (after poling) as an important contributing factor which enhances the piezoelectric response of NBT-based lead-free piezoceramics, we also use dielectric dispersion as a tool to show that the off-stoichiometric composition exhibiting highest piezoelectric response is characterized by maximum suppression of the disordered phase by the poling field.