High temperature oxidation behavior of ZrNiSn-based half-Heusler thermoelectric material

The peculiar oxidation behavior of Zr0.5Hf0.5NiSn0.985Sb0.015 (ZHNS) under different temperatures has been investigated. ZHNS presents thermal inert at 823–1073 K, but shows large oxidation rate at 723–773 K. The thermodynamic and kinetic analyses reveal that, dense oxidation layer (DOL, composed of ZrO2, HfO2 and Ni3Sn2) is preferentially generated at high temperatures and/or low oxygen pressures, while alternative layers of (ZrO2, HfO2, SnO2)/Ni3Sn2 with abundant cracks at lower temperatures. By pre-oxidization at 873 K in Ar flow, an artificial DOL oxidation-protective coating is fabricated. With this coating, the single-leg thermoelectric device demonstrates excellent stability in air at temperature gradient of 778 K/300 K for 15 days.