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Abstract

A series of transmission electron microscopy experiments were carried out for studying the structure and chemistry thermal stability of thermoelectric material single crystalline SnSe with Na-doping. With spherical aberration-corrected scanning transmission electron microscopy and high sensitivity energy dispersive X-ray detector, both of the atomic structural and compositional defects of Na-doped SnSe were uncovered. Lamella-shaped defect with depleted-Sn but rich-Na was captured. In situ heating experiments up to 450 °C revealed a thermal-induced elemental segregation process. The elements of Na, Sn and Se were revealed to segregate severely and even porous regions appeared above 350 °C. Isolated Na, Sn and Se islands were formed through the heating processes. These observations revealed a possible performance degradation of hole-doped SnSe through the applications in thermal cycling processes. A comparison experiment carried out on bulk Na-doped SnSe samples showed a much better thermal stability and a stable electronic transport property. However, the current investigation and results suggest more systematic researches need to be considered to completely preclude or delay the nucleation and propagation of these defects and the thermal-induced elemental segregation processes.

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... With typical sizes down to nanometer scale, the proportion of surface atoms is significantly increased; therefore, nanomaterials often reveal tremendous surface effects but reduced stability compared with bulk materials. Elemental diffusion [6,7], decomposition [8,9], and gas corrosion (such as oxidation [8,10]) more easily occur at elevated temperatures for nanomaterials. Thus, high temperature and related treatment often disturbs/changes the core-shell structures that will, in turn, affect the performance and applications of core-shell nanostructures. ...
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