Unusual Mn oxidation state distribution in the vicinity of the tensile-strained interface between CaMnO3-delta and La0.7Ca0.3MnO3 layers

Oxide perovskite materials with heterointerfaces are important structures with applications such as electronic devices. The functionality of these materials depends on many factors, such as the charge, structure, and presence of defects at the interface. Thus, understanding the properties of interfaces and their effects on material function is important in the design and optimization of functional materials. In this study, the interplay among the Mn oxidation state distribution, the presence of oxygen vacancies (VOs), and the structure of the interface is investigated in the heterointerface between CaMnO3-d and La0.7Ca0.3MnO3 layers by using electron energy loss spectroscopy combined with scanning transmission electron microscopy. Unlike the expectation that the Mn oxidation state distribution is controlled by the distribution of cations intermixing at the interface, it is dominantly influenced by the presence of VOs when the substrate gives tensile stress to it. As a result, the tensile-strained heterointerface shows an anomalously sharp reduction in the Mn oxidation state at the interface. This result suggests that VOs and strain are two essential ingredients to consider for the understanding of oxidation state distribution at interfaces. This study provides insights into the nature of various oxide heterointerfaces.