Synthesis and thermoelectric performance of Li-doped NiO ceramics

Ni1−xLixO (x = 0, 0.03, 0.06, 0.09) powders were prepared by sol–gel method combined with sintering procedure using Ni(CH3COO)2·4H2O and citric acid as the raw materials and alcohol as solvent. The crystal structures of the samples were investigated by X-ray diffraction and Raman spectroscopy. The thermoelectric properties, such as the electrical conductivity, the Seebeck coefficient and the thermal conductivity were measured. The results showed that all the samples are p-type semiconductors. The electrical conductivity increases with the increase of the temperature, which indicates that the substitution of Li+ for Ni2+ can increase the concentrations and mobility of the carriers. The thermal conductivity decreases remarkably with the increase of the Li doping content, which indicates that Li doping can enhance the scattering of phonon. However, the Seebeck coefficient will decline with the increase of the Li doping content. As results of the increase of electrical conductivity and reduction of thermal conductivity, Li doping can increase the figure of merit (ZT) of NiO, the ZT value reach 0.049 at 770 K for Ni1−xLixO with x = 0.06.