Advanced electron microscopy study of structural and electronic properties of charged ordered manganites

电荷有序的锰氧化物代表了一个非常有趣的材料系统，其中四个自由度(晶格、轨道、电荷和自旋)的相互作用导致了令人着迷的输运性质，如外场中金属-绝缘体的转变。到目前为止，无论是相变的机理还是各种相的详细结构都还不是很清楚。实际实验和理论设想表明，不同基态共存和竞争的电子相分离可以控制外场中绝缘体-金属的相变。在本项目中，我们将重点研究Pr1-xCaxMnO3化合物(0.25&lt；x&lt；0.5)，它在外场(磁场、电、光子和应变)中表现出多种开关行为，其电阻变化高达七个数量级。我们将解决几个悬而未决的问题，即电荷和轨道有序的类型，它们与原子结构的联系，有序域的形成，电子相分离的存在和晶界的影响。在研究中，将使用先进的透射式电子显微镜和外场中绝缘体-金属相变的原位电子显微镜测量方法。

Charge ordered manganites represent an extremely interesting material system, where the interplay of four degrees of freedom (lattice, orbital, charge and spin) results in fascinating transport properties such as metal-insulator transitions in external fields. Up to now, neither the mechanisms of the phase transitions nor the detailed structures of the various phases are well understood. Actual experiments and theoretical ideas suggest that electronic phase separation with a coexistence and competition of different electronic ground states could govern the insulator-metal transition in external fields. In this project we will focus on the Pr1-xCaxMnO3 compound (0.25 < x < 0.5) which shows a multitude of switching behavior in external fields (magnetic, electric, photonic and strain) with huge resistance changes of up to seven orders of magnitudes. We will address several unsolved questions, i.e. the type of charge and orbital ordering, their connection to atomic structure, the formation of ordering domains, the presence of electronic phase separation and the influence of grain boundaries. For the investigations, advanced methods of transmission electron microscopy (TEM) and insitu TEM measurements of the insulator-metal transition in external fields will be applied.