Retaining crystallinity of as-deposited thermoelectric Fe2VAl-based thin films grown from DCMS and HiPIMS

Thermoelectric materials have gained much attention in recent years due to their ability to directly interconvert electrical and thermal energy via the Seebeck/Peltier effect. Their appeal for application in energy harvesting and solid-state cooling is however currently held back, as current state-of-the-art systems rely on rare and/or hazardous elements. Efforts to replace them with more abundant and environmentally benign alternatives have shown Heusler-alloys to be attractive candidates with thin film Fe 2 V 0.8 W 0.2 Al achieving a massive Figure of Merit, but requiring extensive post-processing to achieve crystallinity. Here, we report the direct deposition of this material in a crystalline, fully disordered W-type body-centered cubic (bcc) structure using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS). Structural analyses confirm the formation of crystalline Heusler Phases in the as-deposited state, even at room temperature, eliminating the need for prolonged annealing. Transport measurements reveal low thermal conductivity (2.12 W/m∙K), low resistivity (≈240 μΩ∙cm) and a moderate Seebeck-coefficient (−55 μV/K), resulting in a viable Figure of Merit (ZT ≈ 0.1). These findings demonstrate an energy-efficient route in the fabrication of thermoelectric thin films from earth-abundant, non-toxic elements to be used for sustainable energy conversion. • Crystalline and fully disordered W-type bcc-Fe 2 V 0.8 W 0.2 Al in all cases from room temperature up to 500°C in the as-deposited state • Demonstrated the viability of HiPIMS for the production of thermoelectric thin films from non-toxic and earth-abundant elements • Low thermal conductivity (≈ 2 W/m∙K) and moderate Seebeck-coefficient (up to -55 μV /K) lead to a viable Figure of Merit (≈ 0.1) • Increase in deposition pressure appears overall beneficial and leads to an increase in thermopower and a decrease in thermal conductivity • Identified competing growth of (220)- and (440)-orientation linked to deposition parameters and Al-deficiency