Understanding\nthe Anomalous Thermoelectric Behavior\nof Fe–V–W–Al-Based Thin Films

We\ninvestigated the thermoelectric and thermal behavior of Fe–V–W–Al-based\nthin films prepared using the radio frequency magnetron sputtering\ntechnique at different oxygen pressures (0.1–1.0 × 10<sup>–2</sup> Pa) and on different substrates (n, p, and undoped\nSi). Interestingly, at lower oxygen pressure, formation of a bcc-type\nHeusler structure was observed in deposited samples, whereas at higher\noxygen pressure, we have noted the development of an amorphous structure\nin these samples. Our findings indicate that the moderately oxidized\nFe–V–W–Al amorphous thin film deposited on the <i>n</i>-Si substrate possesses a large magnitude of <i>S</i> ∼ −1098 ± 100 μV K<sup>–1</sup> near\nroom temperature, which is almost double the previously reported value\nfor thin films. Additionally, the power factor (PF) indicated an enormously\nlarge value of ∼33.9 mW m<sup>–1</sup> K<sup>–2</sup> near 320 K. The thermal conductivity of the amorphous thin film\nis also found to be 2.75 Wm<sup>–1</sup> K<sup>–1</sup>, which is quite lower compared to bulk alloys. As a result, the\nmaximum figure of merit is estimated to be extremely high, i.e., ∼3.9\nnear 320 K, which is among one of the highest reported values so far.\nThe anomalously large value of Seebeck coefficient and PF has been\nascribed to the unusual composite effect of the metallic amorphous\noxide phase and insulating substrate possessing a large Seebeck coefficient.