Selecting the suitable dopants: electronic structures of transition metal and rare earth doped thermoelectric sodium cobaltate

TL;DR

This study uses ab initio calculations to analyze how different dopants with distinct electronic configurations affect the stability and electronic structure of sodium cobaltate, guiding the design of better thermoelectric materials.

Contribution

It provides a systematic computational analysis of dopant effects on sodium cobaltate, highlighting the stability and electronic impacts of Ni, Zn, and Eu dopants.

Findings

Ni and Zn are more stable when substituting Co.

Eu is more stable when substituting Na.

Results align with experimental data and inform dopant selection.

Abstract

Engineered $Na_{0.75}CoO_2$ is considered a prime candidate to achieve high-efficiency thermoelectric systems to regenerate electricity from waste heat. In this work, three elements with outmost electronic configurations, (1) an open d shell (Ni), (2) a closed d shell (Zn), and (3) a half filled f shell (Eu) with maximum unpaired electrons, were selected to outline the dopants' effects on electronic and crystallographic structures of $Na_{0.75}CoO_2$. Systematic $ab$ $initio$ density functional calculations with $DMOL^3$ package showed that the Ni and Zn were more stable when substituting Co with formation energy $-2.35$ eV, $2.08$ eV when Fermi level equals to the valence band maximum. While Eu is more stable when it substitutes Na having formation energy of $-2.64$ eV. As these results show great harmony with existing experimental data, they provide new insights into the fundamental principle of dopant selection for manipulating the physical properties in the development of high-performance sodium cobaltate based multifunctional materials.