Defect Chemistry Engineering to Regulate the Excellent <i>ZT</i><sub>ave</sub> Value of Nonstoichiometric Ca<sub>3–<i>x</i></sub>Co<sub>4</sub>O<sub>9</sub> (0 ≤ <i>x</i> ≤ 0.06) Ceramics
Zhen Han, Junzhan Zhang, Haolin Ma, Fei Xing, Yuqing Qi, Jian Wei, Geping He, Ying Zhang, Yalou Xin, Qing Wang, Zongmo Shi
Abstract
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 ( ZT ave ) value has hindered service performance. A series of cation vacancies as Ca-active sites were introduced into Ca 3– x Co 4 O 9 (0 ≤ x ≤ 0.06) by defect chemistry engineering to regulate the excellent ZT ave value. The Ca-active sites of Ca 3– x Co 4 O 9 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 2 ) to 0.38 mW/(m·K 2 ) and the electrical conductivity from 54.8 to 108.3 S/cm were achieved for the Ca 2.96 Co 4 O 9 sample. A notable ZT value of 0.32 was obtained at 1073 K. Furthermore, the high ZT ave of approximately 0.166 reached within the temperature range of 323–1073 K, representing a 3.25 times improvement compared to pure Ca 3 Co 4 O 9 ceramics. This study highlights defect chemistry engineering as an effective strategy for optimizing the thermoelectric performance of nonstoichiometric Ca 3 Co 4 O 9 ceramics, offering promising prospects for the development of Ca 3 Co 4 O 9 -based thermoelectric materials.