Synthesis and thermal stability of topological semimetal <i>R</i> MnSb ₂ ( <i>R</i> = Yb, Sr, Ba, Eu)

YbMnSb₂, a topological semimetal with an exotic band structure, has recently been found to exhibit potential thermoelectric transport properties in its single-crystalline formality. The fabrication of polycrystals, which have the advantages of easy synthesis and doping tunability, will advance the transport studies of YbMnSb₂ but face challenges. Here, we found that the polycrystalline YbMnSb₂, synthesized using the conventional melting method, unexpectedly exhibits obvious impurities due to the competing phase YbMn₂Sb₂. To avoid the high-temperature synthesis, high-quality polycrystalline bulk YbMnSb₂, as well as three other <i>R</i>MnSb₂ (<i>R</i> = Sr, Ba, Eu), were successfully prepared by mechanical alloying followed by spark plasma sintering. Based on the high-quality polycrystalline samples, it was discovered that YbMnSb₂ reacts with oxygen during heating in the presence of small amounts of oxygen, resulting in MnSb, Yb₂O₃, and Sb. A similar oxidation phenomenon also occurs for the other <i>R</i>MnSb₂. This work provides a feasible method for synthesizing high-quality <i>R</i>MnSb₂ polycrystals, which should also be suitable for the other isostructural topological semimetals, paving the way for future studies of their transport properties.