Appel Oshrat, Breuer Gil, Cohen Shai, Beeri Ofer, Kyratsi Theodora, Gelbstein Yaniv, Zalkind Shimon
Department of Materials Engineering, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel.
Nuclear Research Centre-Negev, POB 9001, Beer-Sheva 84190, Israel.
Materials (Basel). 2019 May 9;12(9):1509. doi: 10.3390/ma12091509.
The MNiSn (M = Ti; Zr; Hf); half-Heusler semiconducting alloys have a high potential for use as -type thermoelectric materials at elevated temperatures (~1000 K). The alloys' durability is crucial for their commercial handling and use, and therefore it is required to characterize their surface oxidation behavior and stability at the working temperature. X-ray photoelectron spectroscopy was utilized to study the surface composition and oxidation of the ZrNiSn alloy at room and elevated temperatures. It was found that during heating in a vacuum, Sn segregates to the surface in order to reduce the surface energy. Exposing the alloy to oxygen resulted mainly in the oxidation of the zirconium to ZrO, as well as some minor oxidation of Sn. At room temperature, the oxidation to ZrO was accompanied by the formation of a thin ZrO layer at the metal-oxide interface. In contrast to TiNiSn, where most of the oxide was formed on the surface due to oxygen-enhanced segregation of Ti, and in the case of ZrNiSn, the formed oxide layer was thinner. Part of the oxide is formed due to Zr segregation to the surface, and in part due to oxygen dissolved into the alloy.
MNiSn（M = Ti；Zr；Hf）；半赫斯勒半导体合金在高温（约1000K）下作为n型热电材料具有很高的应用潜力。合金的耐久性对于其商业处理和使用至关重要，因此需要表征其在工作温度下的表面氧化行为和稳定性。利用X射线光电子能谱研究了ZrNiSn合金在室温和高温下的表面成分和氧化情况。结果发现，在真空中加热时，Sn会偏析到表面以降低表面能。将合金暴露于氧气中主要导致锆氧化为ZrO，同时Sn也有一些轻微氧化。在室温下，氧化为ZrO伴随着在金属-氧化物界面形成一层薄的ZrO层。与TiNiSn不同，TiNiSn由于Ti的氧增强偏析，大部分氧化物形成在表面，而对于ZrNiSn，形成的氧化层较薄。部分氧化物是由于Zr偏析到表面形成的，部分是由于氧溶解到合金中形成的。
