Competing dopants grain boundary segregation and resultant seebeck coefficient and power factor enhancement of thermoelectric calcium cobaltite ceramics. Issue 14 (1st October 2017)

• Record Type: Journal Article
• Authors: Boyle, Cullen; Liang, Liang; Chen, Yun; Prucz, Jacky; Cakmak, Ercan; Watkins, Thomas R.; Lara-Curzio, Edgar; Song, Xueyan
• Is Part Of: Ceramics international. Volume 43:Issue 14(2017)
• Page Start: 11523
• Page End: 11528
• Publication Date: 2017-10-01
• Subjects: Thermoelectric materials -- Non-stoichiometric addition -- Grain boundary segregation -- Carrier filtering effect; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2017.06.029
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: The present work demonstrates the feasibility of increasing the values of Seebeck coefficient S and power factor of calcium cobaltite Ca3 Co4 O9 ceramics through competing dopant grain boundary segregation. The nominal chemistry of the polycrystalline material system investigated is Ca3−x Bix Bay Co4 O9 with simultaneous stoichiometric substitution of Bi for Ca and non-stoichiometric addition of minute amounts of Ba. There is continuous increase of S due to Bi substitution and Ba addition. The electrical resistivity also changes upon doping. Overall, the power factor of best performing Bi and Ba co-doped sample is about 0.93 mW m −1 K −2, which is one of the highest power factor values ever reported for Ca3 Co4 O9, and corresponds to a factor of 3 increase compared to that of the baseline composition Ca3 Co4 O9. Systematic nanostructure and chemistry characterization was performed on the samples with different nominal compositions. When Bi is the only dopant in Ca3 Co4 O9, it can be found at both the grain interior and the grain boundaries GBs as a result of segregation. When Bi and Ba are added simultaneously as dopants, competing processes lead to the segregation of Ba and depletion of Bi at the GBs, with Bi present only in the grain interior. Bi substitution in the lattice increases the S at both the low and high temperature regimes, while the segregation of Ba at the GBs dramatically increase the S at low temperature regime.