Investigation of structural, morphological, thermal, and thermoelectric properties of Zn1−xCuxAl2O4 (0.0 ≤ x ≤ 0.1)

Abstract

Most promising oxide thermoelectric (TE) materials such as perovskites, layered oxide materials, Al-doped ZnO, etc, have been reported. In the present work, Zn1−x Cu x Al2O4 (0.0 ≤ x ≤ 0.1) samples were synthesized by a simple hydrothermal method. The structural, optical, morphological, and TE properties of Zn1−x Cu x Al2O4 (0.0 ≤ x ≤ 0.1) have been investigated. XRD analysis reveals that ZnAl2O4 has a single-phase cubic structure and Cu is completely dissolved in the ZnAl2O4 lattice. Thermal analysis shows that ZnAl2O4 has high thermal stability up to 1000 °C. From the UV–vis DRS analysis, the energy band gap of ZnAl2O4 decreased from 3.30 eV to 2.82 eV with increasing the content of Cu. Carrier concentration and mobility of the samples were measured by the Hall effect. The values of a carrier concentration of undoped ZnAl2O4 and Zn0.9Cu0.1Al2O4 are obtained to be 3.836 × 1013 cm−3 and 3.3 × 1016 cm−3 at 313 K and 9.6 × 1013 cm−3 for pure and 5.5 × 1016 cm−3 for Zn0.9Cu0.1Al2O4 at 673 K. TE properties of the synthesized samples have been analyzed as a function of temperature. With the optimum values of Seebeck coefficient and electrical conductivity, Zn0.9Cu0.1Al2O4 shows the highest power factor of 0.50 μW/mK2 while the pure ZnAl2O4 shows a maximum power factor of 0.19 μW/mK2 at 673 K. The Zn0.9Cu0.1Al2O4 exhibits a relatively high zT of 2.4 × 10−4 at 673 K, while pure ZnAl2O4 has a zT value of 0.4 × 10−4 at 673 K. The obtained values reveal the improvement of TE properties by increasing the Cu content in the sample.