Whatmore Roger W, Dutta Debismita, Keeney Lynette
Department of Materials, Faculty of Engineering Imperial College London SW7 2AZ United Kingdom.
School of Chemistry University College Cork Cork Ireland.
J Appl Crystallogr. 2025 Jul 2;58(Pt 4):1191-1204. doi: 10.1107/S1600576725004091. eCollection 2025 Aug 1.
Layered crystal structures, such as the Ruddlesden-Popper and Aurivillius families of layered perovskites, have long been studied for their diverse range of functionalities. The Aurivillius family has been extensively studied for its ferroelectric properties and potential applications in various fields, including multiferroic memories. A new analytical model is presented here that explains how out-of-phase boundaries (OPBs) in epitaxial thin films of layered materials affect X-ray diffraction (XRD) peak profiles. This model predicts which diffraction peaks will split and the degree of splitting in terms of simple physical parameters that describe the nanostructure of the OPBs, specifically the structural displacement perpendicular to the layers when moving across the OPB, the angle made by the OPB at the thin-film-substrate interface, and the OPB periodicity and its statistical distribution. The model was applied to epitaxial thin films of two Aurivillius oxides, SrBi(Ta,Nb)O (SBTN) and BiTiO (BiT), and its predictions were compared with experimental XRD data for these materials. The results showed good agreement between the predicted and observed peak splitting as a function of OPB periodicity for SBTN and for an XRD profile taken from a BiT thin film containing a well characterized distribution of OPBs. These results have proven the model's validity and accuracy. The model provides a new framework for analysing and characterizing this class of defect structures in layered systems containing OPBs.
层状晶体结构，如层状钙钛矿的Ruddlesden-Popper和Aurivillius族，长期以来因其多样的功能而受到研究。Aurivillius族因其铁电特性以及在包括多铁性存储器在内的各个领域的潜在应用而得到广泛研究。本文提出了一种新的分析模型，该模型解释了层状材料外延薄膜中的异相边界（OPB）如何影响X射线衍射（XRD）峰轮廓。该模型根据描述OPB纳米结构的简单物理参数预测哪些衍射峰会分裂以及分裂程度，具体包括跨越OPB时垂直于层的结构位移、OPB在薄膜-衬底界面处形成的角度、OPB周期性及其统计分布。该模型应用于两种Aurivillius氧化物SrBi(Ta,Nb)O（SBTN）和BiTiO（BiT）的外延薄膜，并将其预测结果与这些材料的实验XRD数据进行比较。结果表明，对于SBTN以及从包含特征明确的OPB分布的BiT薄膜获取的XRD图谱，预测的和观察到的峰分裂与OPB周期性的函数关系之间具有良好的一致性。这些结果证明了该模型的有效性和准确性。该模型为分析和表征包含OPB的层状系统中的这类缺陷结构提供了一个新框架。
