Nanomaterials - 08

Abstract

A significant improvement in the output power density of the Fe₂VAl-based thermoelectric device is achieved through defect engineering and optimization of a suitable metallization layer. The high thermoelectric performance of Fe₂VAl stems from its sharply rising band edges on either side of the band gap, which is highly sensitive to composition. A slight change in chemical composition could lead to a dramatic change in its thermoelectric properties. Systematic band engineering has already yielded a significantly high thermoelectric power factor (PF) for n-type Fe₂VAl [1,2], enabling its potential use in cooling applications near room temperature. On the other hand, achieving high PF in the p-type counterpart is still challenging [2-4].

We have developed a successful strategy to enhance the thermoelectric power factor of ball-milling and spark plasma sintering processed p-type Fe₂V_0.85Ti_0.1Ta_0.05Al by defects and grain boundary engineering (via controlling the V/Al-defects). Although the obtained ZT is relatively small, the enhancement in PF is quite significant, which enables its use in thermoelectric applications with its n-type Fe₂V_0.95Ta_0.05Al_0.9Si_0.1 counterpart near room temperature. However, a suitable metallization layer is necessary to achieve a minimum internal resistance for the device and convert the maximum produced power. To achieve this, we have systematically studied the metallization of Cu, Ni, and Al under various conditions. Finally, we have developed a two-step sintering process, which enables us to achieve significantly low contact resistance with negligible deterioration in power factor after metallization. We chose Cu metallization and achieved a significantly large power density (ω) of 519.6 mW/cm 2 for a temperature difference of 327 K. The obtained ω is more than 3.3 times that of similar Fe₂VAl-based thermoelectric modules at the same hot side temperature [4]. This study presents a novel approach to enhancing the thermoelectric performance of Fe₂VAl-based devices.