Significant enhancement of the power factor in Ca3Co4O9 by incorporating Cu2Se

Abstract

Composites of calcium cobalt oxide and copper selenide (Ca3Co4O9/xCu2Se, where x = 0, 5, and 10 wt%) were prepared using the polymerized complex method followed by hot-press sintering. X-ray diffraction analysis (XRD) results revealed the crystalline phase of Ca3Co4O9 with low diffraction peaks of Cu2Se phases, indicating that Ca3Co4O9/xCu2Se composites were successfully obtained. Field emission scanning electron microscopy (FESEM) images showed randomly oriented plate-like grains of pristine Ca3Co4O9, while fine grains were observed after incorporation of Cu2Se. Temperature dependence of the electrical resistivity and Seebeck coefficient was investigated using a four-probe method with temperature ranging from 300 K to 862 K. Measurement of the Hall effect showed higher carrier concentration of Ca3Co4O9/xCu2Se composite materials, with increasing Cu2Se contents resulting in decreased electrical resistivity, while the power factor increased with increasing Cu2Se. Lowest electrical resistivity of 115 μΩ m at 862 K was achieved for Ca3Co4O9/10 wt%Cu2Se, while highest Seebeck coefficient of 228 μV K−1 was obtained at 410 K due to phase transition of the Cu2Se matrix. Maximum power factor of Ca3Co4O9/10 wt%Cu2Se was 270 W m−1 K−2, higher than pristine Ca3Co4O9 (104 μW m−1 K−2) at 862 K. The enhanced power factor of Ca3Co4O9/xCu2Se bulk materials occurred as a result of significantly higher hole concentration of Cu2Se, while enhancement of grain connectivity had a strong influence on decreased electrical resistivity.