Power generation driven by thermoelectric conversion requires high chemical stability of the module under the practical operating conditions. The stability of the module in a high-temperature atmosphere depends on the constituent elements of the thermoelectric materials. This study systematically examines the oxidation behaviors of four skutterudite compounds (CoSb₃, Co_0.94Ni_0.06Sb₃, CeFe₃CoSb₁₂, and In_0.25Co₃FeSb₁₂) under high-temperature atmospheric conditions using thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX). All four samples increase in weight at a certain temperature according to the TG curves, and several exothermic peaks are observed in the DTA curves, corresponding to the oxidation or decomposition of the thermoelectric materials. Various phases (e.g., CoSb₂O₄, Sb₂O₃, Sb₂O₄, and CoSb₂O₆ (or FeSbO₄)) are formed after TG-DTA measurement up to 1073 K. The stable temperature ranges of the phases were similar in CoSb₃ and Co_0.94Ni_0.06Sb₃, and in CeFe₃CoSb₁₂ and In_0.25Co₃FeSb₁₂. Notably, the temperature range in which the CoSb₃-type phase is stable is significantly lower in CeFe₃CoSb₁₂ and In_0.25Co₃FeSb₁₂ than in CoSb₃ and Co_0.94Ni_0.06Sb₃. SEM analysis after leaving the sintered materials in air at different temperatures for specified periods of time revealed the formation of several oxide layers on the surface.

RuB₂ (orthorhombic, Pmmn) crystals were grown using metal ruthenium and boron powders using a high-temperature Cu (atomic ratio Cu/Ru = 25.4) solution at 1573 ~ 1773 K, with 5 h keep-time under an Ar atmosphere. Single phase RuB₂ crystals were obtained from the mixture ratios (B/Ru = 2.5 ~ 3.0). For B/Ru = 1.5 ~ 2.2, RuB₂ crystals were formed as a mixed phase with Ru₂B₃ crystals. The hexagonal RuB₂ crystals grew larger with the ratio of B/Ru = 2.5 ~ 3.0. The magnetic susceptibility of RuB₂ showed diamagnetic behavior with almost no temperature dependence from room temperature down to about 80 K, at which a small jump is observed, and Curie-Weiss like paramagnetic behavior observed for further lower temperatures. The electrical resistivity showed low values below 0.142 Ωcm. Single crystals of RuB₂ did not exhibit superconductivity down to temperatures as low as 1.8 K.