Reversible topotactic phase transition between perovskite (PV) and oxygen-vacancy-ordered brownmillerite (BM) structures provides an effective platform for realizing the control of physical properties in complex transition metal oxides. However, such reversibility always requires extreme external conditions, that is, a high temperature and vacuum environment during the PV-BM transition, while an oxidizing atmosphere and relatively low temperature vice versa. Here, we experimentally observe the reversible process in strained La_0.7Sr_0.3MnO_x films at atomic scale by using in-situ heating aberration-corrected scanning transmission electron microscopy (STEM). Apart from the conventional reduction reaction of creating oxygen-vacancy-ordered frameworks after heating in the TEM, the inverse process of BM-to-PV transition is unexpectedly discovered under such an ultra-high vacuum atmosphere (∼10⁻⁹ Torr) at room temperature. Moreover, this abnormal behavior is strain-dependent. The large compressive strain is found to be detrimental to the inverse phase transition. The density functional theory (DFT) calculations show that the high oxygen affinity of La_0.7Sr_0.3MnO_2.5 is responsible for the reversible transitions. Our findings provide a new insight into the redox reactions of manganite and might be further utilized for potential applications in solid fuel cells, oxygen sensors or resistive switching memories.

钙钛矿 (PV) 和氧空位有序褐铁矿 (BM) 结构之间的可逆拓扑相变为实现复杂过渡金属氧化物物理性质的控制提供了有效平台。然而，这种可逆性总是需要极端的外部条件，即PV-BM转变过程中的高温和真空环境，而氧化气氛和相对较低的温度反之亦然。在这里，我们通过实验观察了应变 La _0.7 Sr _0.3 MnO _{x中的可逆过程}通过使用原位加热像差校正扫描透射电子显微镜 (STEM) 在原子尺度上制作薄膜。除了在 TEM 中加热后产生氧空位有序骨架的传统还原反应外，在室温下这种超高真空气氛（~10 ^-9  Torr）下，出人意料地发现了 BM 到 PV 转变的逆过程温度。此外，这种异常行为依赖于应变。发现大的压应变不利于逆相变。密度泛函理论（DFT）计算表明，La _0.7 Sr _0.3 MnO _{2.5的高氧亲和力}负责可逆转换。我们的研究结果为亚锰酸盐的氧化还原反应提供了新的见解，并可能进一步用于固体燃料电池、氧传感器或电阻开关存储器的潜在应用。