Thermoelectric materials that can work at operating temperatures of T ≥ 900 K are highly desirable since the key thermoelectric factors of most thermoelectric materials degrade at high temperatures. In this work, we investigate the high temperature thermoelectric performance of EuFeO3 using a combination of first-principles methods and semi-classical Boltzmann transport theory. High temperature thermoelectric performance is achieved owing to the presence of corrugated flatbands in the valence band region and extremely flatbands in the conduction band region. The lowest energetic structure of EuFeO3 lies within a G-type antiferromagnetic configuration, and the effect of compressive and tensile strains (−7% to +7%) along the (a, b) axes on thermoelectric performance is systematically analyzed. An extremely high value of the Seebeck coefficient (more than 1000 μV/K) is consistently recorded in the high temperature region between 900 K and 1400 K in this material. Furthermore, electrical conductivities and power factors are high and electronic thermal conductivities are low in the considered range of temperatures. The calculated theoretical minimum lattice conductivity is small, estimated at around 1.47–1.54 W m−1 K−1. A compressive strain of −3% is revealed to be the optimum level of strain for enhancing the key thermoelectric factors. Overall, p-type doping shows better thermoelectric performance than n-type doping in EuFeO3.

While most of the thermoelectric materials work well only at low and mid temperatures, high-temperature thermoelectric materials (T > 900 K) are equally important for the operation of deep-spacecraft missions, nuclear reactors, and high-temperature industrial reactors. To accomplish this demand, this work provides insights into wide band gap semiconducting RFeO 3 (rare-earth orthoferrites) for high-temperature thermoelectric applications. Using the first-principles density functional theory calculations, we have demonstrated the coexistence of extremely flat and corrugated flat bands near the Fermi region in a wide band gap material. The presence of such features enhances and sustains the thermopower, electrical conductivity, and power factor, which are the crucial factors for the efficiency of thermoelectric materials. Semiclassical Boltzmann formalism was then employed to study the transport properties of four orthorhombic RFeO 3 materials (R = Pr, Nd, Sm, and Gd). Our results reveal high Seebeck coefficients (thermopower) along with the large electrical conductivities over the high hole doping carrier concentration and in the high-temperature region (T > 900 K). Furthermore, significantly large power factors are obtained with very low theoretical minimum lattice thermal conductivity in the range 1.41−1.51 W m −1 K −1 . These huge power factors directly suggest the maximum power output in RFeO 3 , which we believe is a more appropriate performance index than the figure of merit, especially for hightemperature thermoelectric applications. We also emphasize that the outcomes of our work would be certainly useful for experimentalists in designing high-temperature thermoelectric materials.