Enhanced Oxidation and Thermal Shock Resistance of N-type Mg₂Si_0.89(Sn_0.1,Sb_0.01) Thermoelectric Material via Cr_0.9Si_0.1 Coating

In this study, Cr_0.9Si_0.1 coatings are deposited onto Mg₂Si_0.89(Sn_0.1Sb_0.01) thermoelectric (TE) materials using a closed-field unbalanced magnetron sputtering system. The cyclic oxidation behavior of uncoated and Cr_0.9Si_0.1-coated TE materials is thoroughly investigated at 500 °C for 10 and 50 cycles, with each cycle lasting 1 h. Surface morphology, phase constitution, cross-sectional layer structure, and elemental distribution are analyzed using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Oxidation kinetics are assessed by measuring the mass gain of samples after cyclic oxidation testing. The uncoated TE material exhibits significant surface degradation after cyclic oxidation, initially forming MgO particles, followed by the development of SiO₂ and Mg₂SiO₄ phases in later stages. Encouragingly, the Cr_0.9Si_0.1 coating demonstrates excellent thermal stability on the n-type Mg₂Si_0.89(Sn_0.1Sb_0.01) substrate. Although some oxygen diffusion occurs along grain boundaries within the coating, it is effectively trapped, thereby preventing further penetration into the underlying substrate. The high oxygen affinity of Cr and/or Si atoms plays a critical role in blocking oxidation, offering robust protection. These findings strongly support the use of Cr_0.9Si_0.1 coatings as an effective antioxidant barrier for TE materials under harsh operational conditions, ensuring the long-term operation of TE modules at elevated temperatures.