Na Site Doping a Pathway for Enhanced Thermoelectric Performance in $Na_{1-x}CoO_2$; The Case of Gd and Yb Dopants

M. Hussein N. Assadi

doi:10.1088/1361-648X/ab5bdb

paper

Na Site Doping a Pathway for Enhanced Thermoelectric Performance in $N a_{1 - x} C o O_{2}$ ; The Case of Gd and Yb Dopants

arXiv:2106.12716 · doi:10.1088/1361-648X/ab5bdb

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 $_{2}$ 's 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.

arXiv commentSix figures and Supplementary Materials

Na Site Doping a Pathway for Enhanced Thermoelectric Performance in Na1−x​CoO2​; The Case of Gd and Yb Dopants

Abstract

References in corpus (14)

Na Site Doping a Pathway for Enhanced Thermoelectric Performance in $N a_{1 - x} C o O_{2}$ ; The Case of Gd and Yb Dopants