功能钙钛矿材料中的Jahn-Teller（JT）效应，直接影响材料的结构和物理性能，这种结构转变发生在皮秒(飞秒)时间尺度。超快TEM技术可以直接揭示这类结构转变的动态过程，分析原子重新排列规律。在本项目中，我们将重点关注高温超导材料La2CuO4及庞磁阻材料LaCaMnO单晶中的JT效应，实现对上述材料中光诱导JT相变的原位观察和动力学结构分析。实验技术主要包括原位和超快电子显微术。为了分析动态过程中瞬态的原子结构和电子结构特征及其变化过程，还将以传统的电子晶体学为基础，拓展时间维度，建立晶格动力学的电子显微学分析基础，解释超快过程中晶格的动态变化和重要实验现象。进一步以标准样品的超快结构数据为参考，完善4D电子晶体学分析技术，编写模块化程序，模拟晶格的超快动力学转变过程。

Jahn-Teller (JT) effect is a significant physical phenomenon in functional systems at ps or fs time scale, which always affects the lattice structure and physical characteristics of related materials. Now, the structural changes and atoms rearrangement in the ultrafast dynamic processes such as JT effect can be revealed by applying the ultrafast transmission electron microscopy (UTEM). We will focus on the JT effect in high temperature superconductor (HTS) material La2CuO4 and colossal magnetoresistance (CMR) material LaCaMnO, and achieve the in-situ observation and dynamic structural analysis of the laser induced JT change and phase transition. In order to analyze the instantaneous electronic structure and atomic configuration in dynamic processes, we will extend the traditional electron crystallography by introducing the time parameter and developing the basic theories of 4D crystallography. In this project, we also plan to create modular programs designed for simulating the ultrafast dynamic change of lattices.