Octahedral tilts are the most ubiquitous distortions in perovskite-related structures that can dramatically influence ferroelectric, magnetic, and electronic properties; yet the paradigm of tilt epitaxy in thin films is barely explored. Non-destructively characterizing such epitaxy in three-dimensions for low symmetry complex tilt systems composed of light anions is a formidable challenge. Here we demonstrate that the interfacial tilt epitaxy can transform ultrathin calcium titanate, a non-polar earth-abundant mineral, into high-temperature polar oxides that last above 900 K. The comprehensive picture of octahedral tilts and polar distortions is revealed by reconstructing the three-dimensional electron density maps across film-substrate interfaces with atomic resolution using coherent Bragg rod analysis. The results are complemented with aberration-corrected transmission electron microscopy, film superstructure reflections, and are in excellent agreement with density functional theory. The study could serve as a broader template for non-destructive, three-dimensional atomic resolution probing of complex low symmetry functional interfaces.

中文翻译：

---

功能钙钛矿中八面体倾斜外延的三维原子尺度电子密度重构。

八面体倾斜是钙钛矿相关结构中最普遍的变形，会极大地影响铁电，磁和电子性能。然而，薄膜中倾斜外延的范例几乎没有被探索。对于由轻阴离子组成的低对称复杂倾斜系统，在三维中无损地表征这种外延是一个巨大的挑战。在这里，我们证明了界面倾斜外延可以将超薄的钛酸钙（一种非极性的富含地球的矿物）转变为持续超过900 K的高温极性氧化物。通过重构这三种结构，可以揭示八面体倾斜和极性变形的全面情况使用相干布拉格杆分析，具有原子分辨率的薄膜-电子界面上的三维电子密度图。结果得到像差校正的透射电子显微镜，膜超结构反射的补充，并且与密度泛函理论非常吻合。该研究可以为复杂的低对称功能界面的无损三维原子分辨率探测提供更广泛的模板。