Na site doping a pathway for enhanced thermoelectric performance in Na 1− x CoO 2 ; the case of Gd and Yb dopants
Year: 2019
Type: article
Abstract: Doping is considered to be the main method for improving the thermoelectric performance of layered sodium cobaltate (Na 1− x CoO 2 ). However, in the vast majority of past reports, the equilibrium location of the dopant in the Na 1− x CoO 2 ’ complex layered lattice has not been confidently identified. Consequently, a universal strategy for choosing a suitable dopant for enhancing Na 1− x CoO 2 ’s figure of merit is yet to be established. Here, by examining the formation energy of Gd and Yb dopants in Na 0.75 CoO 2 and Na 0.50 CoO 2 , we demonstrate that in an oxygen poor environment, Gd and Yb dopants reside in the Na layer while in an oxygen rich environment these dopants replace a Co in CoO 2 layer. When at Na layer, Gd and Yb dopants reduce the carrier concentration via electron–hole recombination, simultaneously increasing the Seebeck coefficient ( S ) and reducing electric conductivity ( σ ). Na site doping, however, improves the thermoelectric power factor (PF), only in Na 0.50 CoO 2 . When replacing a Co, these dopants reduce S and PF. The results demonstrate how thermoelectric performance critically depends on the synthesis environment that must be fine-tuned for achieving any thermoelectric enhancement.
Author: M Hussein N Assadi
Institution: UNSW Sydney
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: bronze
Funder: University of New South Wales
OpenAlex ID: W2989609857