通过元素映射揭示的Ca $_3$ Ti $_2$ O $_7$中通过锶取代的层状钙钛矿结构的稳定性
Stabilization of layered perovskite structures via strontium substitution in Ca$_3$Ti$_2$O$_7$ revealed via elemental mapping
摘要：
对层状化合物进行了广泛的研究，从层状铜酸盐到具有共生和堆垛层错的关键问题的范德华材料。然而，由于实验困难，这种结构的研究较少。我们提出了Ruddlesden-Popper钙$_{2.46}$锶$_{0.54}$钛$_2$ O $_7$中共生体的特征缺陷结构，这是已知的混合不适当的铁电性。透射电子显微镜显示，许多共生体组成的7和15层中引入的铁电畴。元素图表明，Sr离子被选择性地取代到钙钛矿层的共生体。密度泛函理论计算支持Sr离子的位置选择性取代，有利地位于共生体中。通过Sr取代的Ruddlesden-Popper相和共生体的稳定化可以由Ca和Sr离子之间的离子半径差来解释。该研究揭示了详细的缺陷结构起源于层状钙钛矿结构的Ca $_{2.46}$ Sr $_{0.54}$ Ti $_2$ O $_7$，并显示了有用的元素映射在探测氧化物中的取代效应。
英文摘要：
Extensive studies have been performed on layered compounds, ranging from layered cuprates to van der Waals materials with critical issues of intergrowths and stacking faults. However, such structures have been studied less because of experimental difficulty. We present characteristic defect structures of intergrowths in the Ruddlesden-Popper Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$, which is known to exhibit hybrid improper ferroelectricity. Transmission electron microscopy reveals that numerous intergrowths composed of 7 and 15 layers are introduced in the ferroelectric domains. Elemental maps demonstrate that Sr ions are selectively substituted into the perovskite layers of intergrowths. Density functional theory calculations support the site-selective substitution of Sr ions, favorably located in the intergrowths. The stabilization of the Ruddlesden-Popper phase and intergrowths via Sr substitution can be explained by the ionic-radius difference between Ca and Sr ions. The study reveals detailed defect structures originating from the layered perovskite structure of Ca$_{2.46}$Sr$_{0.54}$Ti$_2$O$_7$, and shows the usefulness of elemental mapping in probing the substitution effects in oxides.
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