In this work, oxygen vacancies were precisely controlled by manipulating oxygen partial pressure and the oxygen partial pressure dependence of thermoelectric properties of polycrystalline Na0.73CoO2−δ was investigated. The results suggested that resistivity and thermopower augment simultaneously with increasing concentration of oxygen vacancies δ due to the recombination of electrons and holes and average Co valence state. The total thermal conductivity could be reduced by minimizing δ. The dimensionless figure of merit was strongly affected by δ at lower operating temperature. The experimental results provided guideline for the variation in performance of this material system under different processing and operating environments.

Correlation of Oxygen Vacancy Concentration and Thermoelectric Properties in Na0.73CoO2−δ. P.H.Tsai, T.Norby, T.T.Tan, R.Donelson, Z.D.Chen, S.Li: Applied Physics Letters, 2010, 96[14], 141905