A fundamental understanding of oxidation and nitridization behavior in thermoelectric materials contributes to the progress of application as well as basic study of thermoelectricity. This chapter investigates high-temperature tolerance for antimony (Sb) and bismuth (Bi) telluride thermoelectric materials, Antimony telluride (Sb2Te3), (Bi0.5Sb0.5)2Te3, and (Bi0.9Sb0.1)2Te3, under argon, nitrogen, or oxygen gas atmospheres at 0.2 MPa and 547°C. A well-known preparation method for Bi-Te oxides is to mix the required amounts of Bi2O3 with TeO2 and heat them at an elevated temperature for a period until the appropriate reaction occurs. The formation of oxides on the solid surface or the incorporation of oxygen atoms into the solid should be dependent primarily on the thermodynamic activities of constituent elements of the samples under given conditions of temperature and oxygen pressure. The chapter describes the experimental details: design of the thermopiezic analysis apparatus and its instrumental performance, sample preparation, and powder X-ray diffraction.