Thermoelectric Properties of Fe₂VAl-Based Thin-Films Deposited at High Temperature

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Fe₂VAl-based thin-films were prepared using radio frequency magnetron sputtering technique at various substrate temperatures up to 1073 K. At low substrate temperature below 773 K, we did not observe any evidences of L2₁ Heusler phase but the epitaxially grown B2-phase, which is considered as a chemically disordered structure of Heusler-phase. At high substrate temperatures above 773 K, L2₁ ordering became observable and its volume fraction was increased with increasing the substrate temperature. The sample deposited at 1073 K, that was considered as the highly ordered L2₁-phase, possessed S ≈ −120 μV K⁻¹ at around 340 K, and this value is almost the same with that previously reported for bulk samples. The power factor indicated large values exceeding 2.0 mWm⁻¹K⁻² at the room temperature. The thermal conductivity of Fe₂VAl thin-film was reduced to a half value of the bulk. As a result, the maximum figure of merit was almost doubled to 0.07 at 400 K from 0.04 of bulk samples.