Building a free-energy functional from atomically resolved imaging: Atomic-scale phenomena in La-doped BiFeO3
Building a free-energy functional from atomically resolved imaging: Atomic-scale phenomena in La-doped BiFeO3
复制标题
从原子分辨成像构建自由能泛函：La 掺杂 BiFeO3 中的原子尺度现象
DOI：
10.1103/physrevb.99.195440
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发表时间：
2019-05-22
影响因子：
3.7
通讯作者：
Kalinin, Sergei, V
中科院分区：
文献类型：
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作者：
Morozovska, Anna N.;Eliseev, Eugene A.;Kalinin, Sergei, V
扫描透射电子显微镜（STEM）能够以亚微米精度绘制固体的原子结构，为铁性现象和化学膨胀的物理学提供洞察力。然而，由于在波束方向上成像的投影性质，仅信息的子集是可用的。相应地，分析通常依赖于宏观朗道-金斯堡能量的假设已知形式，以及实验确定的原子坐标和序参量场之间的某些预定义关系。在这里，我们提出了一种方法来探索铁性材料的结构，使用降阶参数模型仅根据实验数据构建。本文提出了一个四亚晶格模型（FSM），用于分析描述ABO 3型（反）铁电-反铁畸变钙钛矿中A-阳离子的位移。该模型描述了阳离子A在四个相邻晶胞中的位移，并确定了ABO 3中不同结构相出现和稳定的条件。我们表明，FSM解释的菱形（R），正交（O）和空间调制（SM）相共存，观察原子分辨率STEM在La掺杂的BiFeO 3。使用这种方法，我们原子解决和理论模型的亚晶格不对称性的情况下，A-网站La/Bi阳离子亚晶格LaxBi 1-xFeO 3多晶型物固有的。这种方法允许只从实验数据中探索铁电行为，而不需要对序参量的性质进行额外的假设。
Scanning Transmission Electron Microscopy (STEM) has enabled mapping of atomic structures of solids with sub-pm precision, providing insight to the physics of ferroic phenomena and chemical expansion. However, only a subset of information is available, due to projective nature of imaging in the beam direction. Correspondingly, the analysis often relies on the postulated known form of macroscopic Landau-Ginzburg energy, and some predefined relationship between experimentally determined atomic coordinates and the order parameter field. Here, we propose an approach for exploring the structure of ferroics using reduced order parameter models constructed based on experimental data only. We develop a four sublattices model (FSM) for the analytical description of A-cation displacement in (anti)ferroelectric-antiferrodistortive perovskites of ABO3-type. The model describes the displacements of cation A in four neighboring unit cells and determines the conditions of different structural phases appearance and stability in ABO3. We show that FSM explains the coexistence of rhombohedral (R), orthorhombic (O) and spatially modulated (SM) phases, observed by atomic-resolution STEM in La-doped BiFeO3. Using this approach, we atomically resolve and theoretically model the sublattice asymmetry inherent to the case of the A-site La/Bi cation sublattice in LaxBi1-xFeO3 polymorphs. This approach allows exploring the ferroics behaviors from experimental data only, without additional assumptions on the nature of the order parameter.