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, Zn _1− _x Cu _x Al _2 O _4 (0.0 ≤ x ≤ 0.1) samples were synthesized by a simple hydrothermal method. The structural, optical, morphological, and TE properties of Zn _1− _x Cu _x Al _2 O _4 (0.0 ≤ x ≤ 0.1) have been investigated. XRD analysis reveals that ZnAl _2 O _4 has a single-phase cubic structure and Cu is completely dissolved in the ZnAl _2 O _4 lattice. Thermal analysis shows that ZnAl _2 O _4 has high thermal stability up to 1000 °C. From the UV–vis DRS analysis, the energy band gap of ZnAl _2 O _4 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 ZnAl _2 O _4 and Zn _0.9 Cu _0.1 Al _2 O _4 are obtained to be 3.836 × 10 ^13 cm ^−3 and 3.3 × 10 ^16 cm ^−3 at 313 K and 9.6 × 10 ^13 cm ^−3 for pure and 5.5 × 10 ^16 cm ^−3 for Zn _0.9 Cu _0.1 Al _2 O _4 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, Zn _0.9 Cu _0.1 Al _2 O _4 shows the highest power factor of 0.50 μ W/mK ^2 while the pure ZnAl _2 O _4 shows a maximum power factor of 0.19 μ W/mK ^2 at 673 K. The Zn _0.9 Cu _0.1 Al _2 O _4 exhibits a relatively high zT of 2.4 × 10 ^−4 at 673 K, while pure ZnAl _2 O _4 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.

Keywords

• thermoelectric properties
• spinel oxides
• seebeck coefficient
• figure of merit