Abstract
Although theoretical studies and experimental investigations have demonstrated the presence of space-charge-induced dopant segregation, most work has been confined largely to the crystal-free surface and some special grain boundaries, and to the best of our knowledge there has been no systematic comparison to understand how the segregation varies at different types of interfaces in polycrystals. Here, through atomic-column resolved scanning transmission electron microscopy in real polycrystalline samples, we directly elucidate the space-charge segregation features at five distinct types of interfaces in an ABO3 perovskite oxide doped with A- and B-site donors. A series of observations reveals that both the interfacial atomic structure and the subsequent segregation behaviour are invariant regardless of the interface type. The findings in this study thus suggest that the electrostatic potential variation by the interface excess charge and compensating space charge provides a crucial contribution to determining not only the distribution of dopants but also the interfacial structure in oxides.
Highlights
Theoretical studies and experimental investigations have demonstrated the presence of space-charge-induced dopant segregation, most work has been confined largely to the crystal-free surface and some special grain boundaries, and to the best of our knowledge there has been no systematic comparison to understand how the segregation varies at different types of interfaces in polycrystals
It is considerably time consuming during scanning transmission electron microscopy (STEM) observation to identify suitable interfaces parallel to a low index plane in the polycrystalline microstructure consisting of numerous grains with a completely random orientation (see the crystallographic orientation map of grains and the orientation-distribution pole figure obtained in our polycrystalline (Ca1/4Cu3/4)TiO3 samples via the electron backscattered diffraction (EBSD) analysis in Supplementary Fig. 3)
The high-angle annular dark-field (HAADF)-STEM images presented in Fig. 2b show typical microstructure observed in our samples
Summary
Theoretical studies and experimental investigations have demonstrated the presence of space-charge-induced dopant segregation, most work has been confined largely to the crystal-free surface and some special grain boundaries, and to the best of our knowledge there has been no systematic comparison to understand how the segregation varies at different types of interfaces in polycrystals. A series of follow-up studies by Kliewer and colleagues[3,4,5,6] in the mid-1960s theoretically consolidated the existence of space charge and systematically calculated the variation of space-charge potential and the resulting distribution of vacancies and aliovalent impurities in ionic halide crystals by taking the long-range columbic interaction and even the electron affinity into account Spurred by these milestone works, many notable experimental observations as well as theoretical calculations have been carried out in order to shed light on the dopant segregation behaviour and subsequent correlation with the space charge in ionic crystals[7,8,9,10,11,12,13,14,15,16]. Even though the basic ideas derived for the free surface have been adopted to explain the overall segregation characteristics at other types of interfaces including grain boundaries, to the best of our knowledge no specific comparison of segregation between different interfaces has been made, and as a result there is a lack of understanding regarding the influence of the interface type and structure
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