Superior thermoelectric power factor in BiCuSeO enabled by ferromagnetic metallic phase and spin entropy effect

Abstract BiCuSeO, a layered oxychalcogenide is a potential p-type thermoelectric material for mid-temperature waste heat recovery. In this work, the BiCuSeO was synthesized by two step facile process of ball milling followed by hot press densification technique. Efforts to increase the reaction speed and time leads to a preferential formation of composite, in which ferromagnetic metallic phase Bi2Cu(SeO3)4 is embedded in the BiCuSeO matrix. X-ray diffraction and X-ray photoelectron spectroscopy analysis confirms the presence of secondary phase Bi2Cu(SeO3)4 in the matrix. The temperature dependent VSM shows the increasing trend of magnetic moment with temperature reveals the ferromagnetic nature of Bi2Cu(SeO3)4. Over the temperature, the electrical conductivity (σ) decreases confirms the metallic behaviour of the sample with high σ of 92.48 Scm-1 at 303 K. Meanwhile, the deterioration of Seebeck coefficient was negligible compared with pure because of additional spin entropy effect confirmed from the EPR analysis with g-factor value of 2.278. Consequently, the occurrence of ferromagnetic metallic phase results in high thermoelectric power factor of 493.73 μWm-1K-2 at 303 K which is 37% higher than pure BiCuSeO.