Impact of Oxygen Stoichiometry on the Thermoelectric Properties of BiSrCoO Thin Films.

In this study, we present a comprehensive analysis of the thermoelectric (TE) properties of highly -axis-oriented thin films of layered misfit cobaltates BiSrCoO. The films exhibit a high -axis orientation, facilitating precise measurements of electronic transport and TE properties along the - crystallographic plane. Our findings reveal that the presence of nearly stoichiometric oxygen content results in high thermopower with metallic conductivity, while the annealing of the films in a reduced oxygen atmosphere eliminates their metallic behavior. According to the well-established Heike's limit, the thermopower tends to become temperature independent when the thermal energy significantly exceeds the bandwidth, which provides a rough estimation of charge carrier density by using the Heike's formula. This observation suggests that the dominant contribution to the thermopower comes from the narrow Co-t bands near the Fermi energy. Our study demonstrates that the calculated thermopower value using Heike's formula, based on the Hall electron density of the BiSrCoO thin films at 300 K, aligns well with the experimental results, shedding light on the intriguing TE properties of this family of layered cobaltate oxide films.