CuAlO \(_{2}\) as an oxide thermoelectric material has attracted researchers’ attention because of its low-cost and high-temperature stability. In this work, CuAl \(_{1-x}\) O \(_{2}\) + Gd \(_{x}\) (x=0, 0.01, 0.03, 0.04, 0.06, 0.1) samples were synthesized by solid-state reaction and spark plasma sintering. Positron annihilation measurements showed that doping with a small amount of Gd ( \(x \le\) 0.03) inhibits the growth of Cu vacancy and vacancy cluster size, which improves the carrier mobility of the sample and optimizes the electrical conductivity and power factor of the sample. With further increase of Gd content, both the vacancy cluster size and concentration shows increase, which leads to fast decrease of the mobility. Finally, the sample CuAl \(_{0.97}\) O \(_{2}\) +Gd \(_{0.03}\) exhibits the best thermoelectric performance at 773 K, with the highest zT value of 5.824 \(\times\) 10 \(^{-3}\) , which is 40.39% higher than that of the intrinsic CuAlO \(_{2}\) . The average zT of CuAl \(_{0.97}\) O \(_{2}\) +Gd \(_{0.03}\) between 303 K and 773 K is also 38.9% higher than that of the intrinsic sample.
