Thermoelectric Properties of Zinc Oxide Doped with Aluminum and Nickel Ions

In this work, a thermoelectric material with the nominal composition Zn_0.97Al_0.02Ni_0.01O is synthesized using the chemical coprecipitation method. The synthesized powder consists of the main phase of wurtzite with a small content of Ni_1–zZn_zO; the change in the crystal-lattice parameters of the main phase indicates the replacement of Zn²⁺ with Al³⁺. The Ni_1–zZn_zO phase is predominantly located at the grain boundaries, blocking their growth during spark-plasma sintering. The resulting morphology enhances phonon scattering processes, which leads to a decrease in thermal conductivity. The electrical conductivity exhibits activation behavior and increases significantly in comparison with undoped ZnO, because the concentration of charge carriers increases with the substitution of Zn²⁺/Al³⁺. Thus, the chemical coprecipitation method allows one to obtain doped ZnO with an increase in thermoelectric performance of more than 2 times relative to undoped ZnO.