Thermoelectrics in misfit-layered oxides [(Ca,Ln)2CoO3]0.62[CoO2]: From bulk to nano

• Published in: Nano energy 2012-05, Vol.1 (3), p.456-465
• Main Authors: Wang, Yang, Sui, Yu, Li, Fang, Xu, Luxiang, Wang, Xianjie, Su, Wenhui, Liu, Xiaoyang
• Format: Article
• Language: English
• Subjects: Layered cobaltite; Nanocrystal; Thermal conductivity; Thermoelectrics
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2012.02.007

Thermoelectric (TE) properties of [(Ca,Ln)2CoO3]0.62[CoO2] family, including ceramic bulks synthesized by a solid-state reaction and nano-sized compacts fabricated by a simple cold-pressure method, are systematically investigated, in terms of nanocrystallization technology, effects of doped rare-earth Ln ions, and doping level. The doped Ln ions have noticeable influences on the TE characteristics of [Ca2CoO3]0.62[CoO2] system. The substitutions of Ln3+ for Ca2+ change hole concentration and meanwhile introduce a strong point-defect phonon scattering. From Ln=La to Yb, the increased structural distortion, enhanced electron correlation, and increasing ionic mass fluctuation are responsible for the different TE response. Furthermore, compared with the ceramic bulks, in the highly textured nano-sized compacts the thermal conduction is efficiently suppressed. A doubling of ZT has been achieved by the nanoengineering (ZT exceeds 0.45 at 1000K). On the basis of these results, some strategies for further improvement in ZT are proposed. [Display omitted] ► Highly-textured nano-sized [(Ca,Ln)2CoO3]0.62[CoO2] compacts are successfully fabricated by a simple cold-pressure method. ► These nanocompacts exhibit a high thermoelectric efficiency. ► The high ZT value that exceeds 0.45 at 1000K is maintained after intensive thermal cycling in air. ► This nanosystem could be a promising thermoelectric oxide for high temperature applications.