Complex defect formation in Fe doped γ-CuI: Enhancement of thermoelectric properties via band engineering

Abstract

The doping effect of Fe atoms on CuI, a potential candidate for room temperature thermoelectric materials, was investigated due to the lack of studies for the aspect of band engineering. The addition of Fe atoms was observed to enhance the p-type performance of CuI, although Fe is more suitable as a donor material. Through Mossbauer spectroscopy and Density Functional Theory (DFT) calculations, it was determined that only about 5 % of the added Fe atoms simply substitute Cu sites, while most Fe atoms occupy interstitial sites, acting as defects and promoting Cu vacancies. Despite the trace amount of Fe only contribute to magnetic properties, it was found that multiple defects and deformation in the electronic band structure caused the effective mass to nearly double. As a result, electrical conductivity increased by an order of magnitude, while the decrease in the Seebeck coefficient was less than half, demonstrating a violation of the Pisarenko relation. Additionally, the incorporation of Fe atoms induced nano structuring behavior, increasing boundary scattering in CuI and significantly reducing thermal conductivity. Fe could be suggested as a suitable dopant for the "phonon-glass-electron-crystal" strategy.