Understanding the anomalous thermoelectric behaviour of Fe-V-W-Al based thin films

We have investigated the thermoelectric and thermal behaviour of Fe-V-W-Al based thin films prepared using radio frequency magnetron sputtering technique at different base pressures (0.1 ~ 1.0 X 10-2 Pa) and on different substrates (n, p and undoped Si). Interestingly, at lower base pressure, formation of bcc type of Heusler structure was observed in deposited samples, whereas at higher base pressure, we have noted the development of non-Heusler amorphous structure in these samples. Our findings indicates that the moderately oxidized Fe-V-W-Al amorphous thin film deposited on n-Si substrate, possesses large magnitude of absoulte S ~ 1098 microvolt per kelvin near room temperature, which is almost the double the previously reported value for thin films. Additionally, the power factor indicated enormously large values ~ 33.9 milliwatt per meter per kelvin sqaure near 320 K. The thermal conductivity of the amorphous thin film is also found to be 2.75 watt per meter per kelvin, which is quite lower compared to bulk alloys. As a result, the maximum figure of merit is estimated to be extremely high i.e. ~ 3.9 near 320 K, which is among one of the highest reported values so far. The anomalously large value of Seebeck coefficient and power factor has been ascribed to formation of amorphous structure and composite effect of thin film and substrate.