The effects of composition deviations on the microstructure and thermoelectric performance of Ca3Co4O9 thin film
This work investigated composition deviations in Ca3Co4O9 (CCO) films during rf-sputtering process and their effects on the properties of post-annealed CCO films. The negative oxygen ions produced during sputtering resulted in a great reduction in deposition rate and preferential re-sputtering of calcium atoms from the substrate due to their lighter weight compared to cobalt. Experiment results showed that the single phase CCO film exhibited the lowest electrical resistivity of ~ 4 mΩ cm at room temperature and a high power factor of ~ 1.1 mW/mK2 at 973 K. Compared with the single phase CCO sample, the resistivity of the Co-rich sample increased slightly and the Seebeck coefficient increased by ~ 20% at high temperature, thereby leading to a high power factor. The upturn of the Seebeck coefficient behaviours in Co-rich samples from 700 K is most likely associated with the strain induced by the mismatch of thermal expansion coefficients (CTE) between CCO and Co3O4 grains.
This project is supported by Australian Research Council (Grant Nos. DP0988687, DP110102662, FT100100956 and LP120200289) and Foundation of Shaanxi University of Science & Technology (2017GBJ-03).
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