Product Identification of Bismuth Telluride by Nitric Acid Corrosion

Bismuth telluride-based thermoelectric devices are the only thermoelectric devices that are currently used in large-scale commercial applications. In actual production, nitric acid roughening solution corrodes them and generates a black substance on the surface that is difficult to remove. The exact composition of the black film is not known, which makes its removal even more difficult. In this study, it was observed by x-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) that the black substance may be formed by the reaction of Sb 2 Te 3 in p -type bismuth telluride with nitric acid. Valence analysis by x-ray photoelectron spectrometry (XPS) showed the presence of Te in the black substance in the valence states of Te 4+ and Te 6+ , and Sb in the valence state of Sb 3+ . Fourier transform infrared spectrometry (FTIR) results showed the existence of four chemical bonds, including ν Te-O , ν Sb-O , ν Te-O-Te , and ν Te-O-Te , while ν N=O and δ N=O were also detected at 1361 cm −1 and 1039 cm −1 , respectively, indicating the presence of NO3 − in the black substance. Synthesizing the experimental phenomena and literature data, the composition of the black substance was presumed to be x TeO 2 -Sb 2 O 3 -HNO 3 (2 < x < 3), and the corresponding reaction chemical equation was given. This study provides an important reference for further optimization of the production process.