Thermoelectric properties of Al-doped zinc oxide-based ceramics sintered at high temperature under different atmospheres

The conventional Solid-state reaction (SSR) method was used to synthesize compositions of (Zn_1−xAl_x)O, with x varying from 0.005 to 0.05 respectively. The as-prepared compositions were sintered in the air as well as in an argon atmosphere at 1400 °C, and their phases, microstructures and thermoelectric properties were investigated. Single-phase ceramics were formed for the composition with x ≤ 0.02. However, some unknown phases (∆) developed along with the parent phases for x ≥ 0.01 due to an over solubility limit of Al in Zn sintered in the air atmosphere. The highest Power factor (PF) for both air and an argon atmosphere were obtained 8.886 × 10⁻⁴ WK⁻² m⁻¹ and 5.389 × 10⁻⁴ WK⁻² m⁻¹ while, the lowest electrical resistivity (ρ) for the composition with x = 0.02 i.e. (Zn_0.98Al_0.02)O were obtained 7.674 mΩ cm and 1.430 mΩ cm at 702 °C respectively. The PF obtained in the air sintered atmosphere for the composition with x = 0.02 is 1.648 times higher than for the same composition sintered in an argon atmosphere. The ρ for the composition with x = 0.02 sintered in an argon atmosphere is 4.6202 times lowered for the same composition (x = 0.02) sintered in the air atmosphere.