Thermoelectric and magnetic properties of Ca3Co4–xCuxO9 + δ with x = 0.00, 0.05, 0.07, 0.10 and 0.15

Ca3Co4–xCuxO9 + δ (x = 0.00, 0.05, 0.07, 0.10 and 0.15) samples were prepared by conventional solid-state synthesis and their thermoelectric properties were systematically investigated. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. Ca3Co3.85Cu0.15O9 + δ had the highest power factor of 2.17 μW cm−1 K−2 at 141 K, representing an improvement of about 64.4% compared to undoped Ca3Co4O9 + δ. Magnetization measurements indicated that all the samples exhibit a low-spin state of cobalt ions. The observed effective magnetic moments decreased with increasing copper content.