Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, Xi'an Jiaotong University , Xi'an 710049, China.
Department of Chemistry and 4D Laboratories, Simon Fraser University , Burnaby, British Columbia V5A 1S6, Canada.
ACS Appl Mater Interfaces. 2017 Aug 30;9(34):28716-28725. doi: 10.1021/acsami.7b04033. Epub 2017 Aug 15.
Bismuth sodium titanate, BiNaTiO (BNT), is a promising lead-free ferroelectric material. However, its potential applications have not been fully explored, mainly because of the complex domain structure arising from its intricate phase transitions. A deep and thorough study of its domain structure and polarization switching behavior will greatly help with understanding the polarization nature and with promoting future applications. In this work, we demonstrate that BNT polycrystalline films possess a highly ordered out-of-plane polarization (self-polarization) and randomly oriented in-plane polarizations. Interestingly, the inherent nature of polarization in the BNT films does not allow for the nonvolatile domain writing, as the switched polarization spontaneously and rapidly reverses to the initial orientation state once the external poling electric field is removed, making the self-polarization recoverable. Such a stable self-polarization vanishes gradually with temperature increasing over 150 °C but starts to recover to its initial state upon cooling down to 250 °C, and entirely recovers once the temperature is reduced to below 200 °C. Such interesting properties of BNT films are attributed to the combined effects of the free charges at the Pt electrode, (detected) cation vacancies at the oxide/Pt interface and the defects in oxide lattices. Our results make a step closer to fully understand the nature of polarization and related piezoelectricity in BNT. Such films with recoverable self-polarization are of great interest for applications as sensors, actuators, and transducers that can operate particularly under high temperatures and high electric field conditions.
钛酸铋钠（BNT）是一种很有前途的无铅铁电材料。然而，其潜在的应用尚未得到充分的探索，主要是因为其复杂的相转变产生了复杂的畴结构。深入彻底地研究其畴结构和极化翻转行为将有助于理解极化的本质，并促进未来的应用。在这项工作中，我们证明了 BNT 多晶薄膜具有高度有序的面外极化（自极化）和随机取向的面内极化。有趣的是，BNT 薄膜中极化的固有性质不允许进行非易失性畴写入，因为一旦去除外部极化电场，翻转的极化就会自发且迅速地反向回到初始取向状态，从而使自极化可恢复。这种稳定的自极化随着温度超过 150°C 逐渐消失，但在冷却到 250°C 以下时开始恢复到初始状态，一旦温度降至 200°C 以下，就会完全恢复。BNT 薄膜的这些有趣性质归因于 Pt 电极上的自由电荷、氧化物/Pt 界面上的（检测到的）阳离子空位以及氧化物晶格中的缺陷的共同作用。我们的结果使人们对 BNT 中极化的本质和相关压电性有了更深入的了解。这种具有可恢复自极化的薄膜在传感器、执行器和换能器等应用中非常有吸引力，因为它们可以在高温和高电场条件下特别工作。
