Defect Chemistry Engineering to Regulate the Excellent Value of Nonstoichiometric CaCoO (0 ≤ ≤ 0.06) Ceramics.

Cobalt-based oxides have attracted significant attention as p-type thermoelectric materials due to their wide operational temperature range. However, their low average figure of merit () value has hindered service performance. A series of cation vacancies as Ca-active sites were introduced into CaCoO (0 ≤ ≤ 0.06) by defect chemistry engineering to regulate the excellent value. The Ca-active sites of CaCoO ceramics induced lattice distortion and point defects, which were unequivocally confirmed by the iDPC-STEM results. The power factor from 0.18 mW/(m·K) to 0.38 mW/(m·K) and the electrical conductivity from 54.8 to 108.3 S/cm were achieved for the CaCoO sample. A notable value of 0.32 was obtained at 1073 K. Furthermore, the high of approximately 0.166 reached within the temperature range of 323-1073 K, representing a 3.25 times improvement compared to pure CaCoO ceramics. This study highlights defect chemistry engineering as an effective strategy for optimizing the thermoelectric performance of nonstoichiometric CaCoO ceramics, offering promising prospects for the development of CaCoO-based thermoelectric materials.