有序化氧空位SrCoOx结构和性能的光学调控

The manipulation of oxygen vacancies is critical for the structures and functionalities of transition metal oxides. Because of the exceptionally low oxygen activation energies, the low-temperature topotactic transitions between different phases of SrCoOx are mutable with the modification of the ambient conditions including strain, electric field and temperature.etc, making SrCoOx a prime platform for studying the role of oxygen stoichiometry in determining its physical properties. Besides the study of intrinsic characteristic under equilibrium states, transient behaviors upon excitation of ultrafast laser pulses are also highly required. Giant photoinduced strain (Δc/c>1%) has been observed in applicant’s previous studies and was presumptively attributed to the rearrangement of the tilted Co-O octahedral that induced by the laser pump. In this project, we propose to combine the half-Bragg-diffraction and extended x-ray absorption fine structure techniques with ultrafast X-ray methods to give the direct evidence of the latent transient rotation of octahedral, revealing the physical origin of the giant photoinduced lattice response and the role oxygen vacancies played in this mechanism. Our project will provide a novel manipulation scheme “Light-octahedral rotation-performance”, which has the great meaningfulness of sorting out the relationship between the crystal structure and physical property with correlated electron systems.

氧空位对过渡金属氧化物结构和性能的调控意义重大，SrCoOx较低的氧激活能使其氧空位极易受到外延应变、电场和高压等外场调控而发生拓扑相变，成为研究价态变化与物性关联的理想平台；但除了稳态调控以外,材料在瞬态激发下所展现出的各种新颖的非平衡态特性也至关重要。申请者前期开展了SrCoO2.5在激光调控下的瞬态特性研究，观测到超强的光致应变(Δc/c>1%)，并推测该巨幅应变源自光场诱导的Co-O八面体旋转行为。本项目拟将同步辐射装置半指数衍射法、扩展X射线吸收精细结构谱与超快X射线探测技术相结合，发展瞬态光致氧八面体转动的实验标定手段，对Co-O八面体的瞬态旋转进行表征，从而揭示光致晶格响应的物理机制，并明确有序化氧空位从中所起的作用。本项目提供了一种新颖的性能调控手段：“光-氧八面体旋转-性能”，对理解此类关联电子体系中晶体结构与物理性能具有不可或缺的意义。

课题执行周期内完成了既定的研究目标及任务，即发展并依托新型的超快X射线探测技术，并研究了有序化氧空位体系由光激发所产生的，持续时间非常短（纳秒和微秒量级）的瞬态晶格响应，从而建立起一种新型的材料物性参数和结构性能的调控手段。并取得以下三个方面的研究成果：1. 建立和发展了超快X射线谱学和衍射探测装置，并基于该表征平台实现了有序化氧空位瞬态结构响应的原位表征，捕捉到纳秒量级的瞬态氧八面体晶格旋转，完成项目研究计划；2. 拓展超快X射线衍射探测技术到新颖的研究体系（PTO/PO），发现更为新颖的光生退极化场及光致热效应所产生的应变调控竞争机制；3. 将常规的超快X射线探测技术，拓展为适用于金属增材制造及动态加载等不可逆过程的原位表征，极大地丰富了该技术所适用的研究领域。