Bismuth sodium titanate and related compounds are promising lead-free ferroelectric materials potentially useful in a wide range of piezoelectric applications. The domain structure plays an important role in determining the piezoelectric and ferroelectric properties and thereby the performance of electromechanical transducers. In this work, piezoresponse force microscopy (PFM) is used to gain insights into the mesoscopic-scale domain structure and its evolution under electric field in the (1−x)Bi_0.5Na_0.5TiO₃-xBaTiO₃ (BNT-BT) piezoceramics with compositions varying from x = 0 to x = 0.08. A phase transition from the rhombohedral phase to the tetragonal phase is observed with increasing BT contents. A relationship is established between the relaxor behavior and the domain structures imaged by PFM, i.e., short-range polar regions without visible domains in relaxor ceramics of pure BNT, while long-range ordered polar states with clear domains in ferroelectric ceramics with the addition of BT content. Distinct micro-domains are observed in the ceramics with compositions close to the morphotropic phase boundary (MPB), but the domain size drops to nanometers in the MPB composition with an increasing domain wall density. An electric field can induce the transformation from the relaxor behavior to a ferroelectric state, accompanied by an increase in domain sizes and a rearrangement/reorientation of the polar domains. This study of domain structure and its evolution in BNT-BT provides a better understanding of the relationship between the crystal structure, mesoscopic-scale domains, and macroscopic properties in these important lead-free piezoelectric ceramics.

中文翻译：

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无铅Bi0.5Na0.5TiO3-BaTiO3铁电陶瓷介观畴结构和宏观性能的演变

钛酸铋钠和相关化合物是有前途的无铅铁电材料，可广泛用于压电应用中。畴结构在确定压电和铁电特性以及机电转换器的性能方面起着重要作用。在这项工作中，使用压电响应力显微镜（PFM）来深入了解（1- x）Bi _0.5 Na _0.5 TiO ₃ - x BaTiO ₃（BNT-BT）中介观尺度域结构及其在电场下的演化。组成从x  = 0到x的压电陶瓷 = 0.08。随着BT含量的增加，观察到从菱面体相到四方相的相变。在弛豫器行为和PFM成像的畴结构之间建立了关系，即纯​​BNT弛豫陶瓷中没有可见畴的短程极性区域，而铁电陶瓷中通过添加铁氧体具有清晰畴的长程有序极性态BT内容。在陶瓷中观察到明显的微区，其组成接近相变相界（MPB），但是随着畴壁密度的增加，MPB组成中的畴尺寸下降到纳米。电场可引起从弛豫行为转变为铁电态，并伴随着畴尺寸的增加和极性畴的重排/​​重新取向。