Studying the Seebeck coefficient and exploring the possibility of enhancing ZT upto 1.8 for NaCo$_2$O$_4$ in high temperature region

TL;DR

This study combines experimental and computational methods to analyze the Seebeck coefficient of NaCo$_2$O$_4$, revealing potential to enhance thermoelectric efficiency (ZT) up to 1.8 at high temperatures through doping.

Contribution

It provides a detailed electronic structure analysis and predicts significant ZT enhancement in NaCo$_2$O$_4$ via p- and n-type doping at high temperatures.

Findings

Seebeck coefficient ranges from 55 to 103 μV/K between 300-600 K.

Maximum ZT of 1.8 predicted for n-type doping at 1200 K.

Electronic structure shows magnetic and half-metallic nature.

Abstract

Here, we have studied the temperature dependent Seebeck coefficient (S) of the NaCo$_2$O$_4$ (NCO) by using experimental and computational methods. The range of experimentally obtained S is $\sim$55 to 103 $\mu$V/K in the temperature range of 300-600 K, which confirms the p-type behaviour of NCO. The electronic structure of this compound is obtained via DFT+U formalism. The band dispersion and partial density of states confirms the magnetic and half metallic nature. Furthermore, in the transport properties, the obtained S using a U = 4 eV gives the best match with experimental data. The temperature and chemical potential dependent S$^{2}$$\sigma$$/$$\tau$ is calculated using the obtained electronic transport properties, in which the maximum value obtained for p(n)-type doping is $\sim$22(61)$\times$10$^1$$^4$ $\mu$WK$^{-2}$cm$^{-1}$s$^{-1}$. The possibility of enhancing the ZT is identified, and it is calculated in temperature range 300-1200 K. The maximum calculated value of ZT is 0.64 for p-type and 1.8 for n-type doping at 1200 K. The calculated carrier concentration obtained for p(n) type doping at 1200 K is $\sim$1.17 (1.6)$\times$10$^2$$^2$ cm$^-$$^3$. This study suggests that the careful doping of p and n type can enhance the applicability of this compound in thermoelectric for high temperature application.