High-Performance Thermoelectric Oxides Based on Spinel Structure

TL;DR

This study uses density functional theory to identify spinel-structured oxides with high Seebeck coefficients and promising thermoelectric properties at near room temperature, potentially replacing toxic materials.

Contribution

It predicts new high-performance thermoelectric oxides within the spinel structure, specifically MnFe₂O₄, RhFe₂O₄, CrFe₂O₄, and MoFe₂O₄, with high Seebeck coefficients and favorable thermoelectric power factors.

Findings

MnFe₂O₄ and RhFe₂O₄ have Seebeck coefficients of ~±600 μV/K at room temperature.

CrFe₂O₄ and MoFe₂O₄ exhibit even higher Seebeck coefficients (~±700 μV/K).

MoFe₂O₄ doped with holes shows a high thermoelectric power factor at 300 K and 600 K.

Abstract

High-performance thermoelectric oxides could offer a great energy solution for integrated and embedded applications in sensing and electronics industries. Oxides, however, often suffer from low Seebeck coefficient when compared with other classes of thermoelectric materials. In search of high-performance thermoelectric oxides, we present a comprehensive density functional investigation, based on GGA$+U$ formalism, surveying the 3d and 4d transition-metal-containing ferrites of the spinel structure. Consequently, we predict MnFe$_2$O$_4$ and RhFe$_2$O$_4$ have Seebeck coefficients of $\sim \pm 600$ $\mu$V K$^{-1}$ at near room temperature, achieved by light hole and electron doping. Furthermore, CrFe$_2$O$_4$ and MoFe$_2$O$_4$ have even higher ambient Seebeck coefficients at $\sim \pm 700$ $\mu$V K$^{-1}$. In the latter compounds, the Seebeck coefficient is approximately a flat function of temperature up to $\sim 700$ K, offering a tremendous operational convenience. Additionally, MoFe$_2$O$_4$ doped with $10^{19}$ holes/cm$^3$ has a calculated thermoelectric power factor of $689.81$ $\mu$W K$^{-2}$ m$^{-1}$ at $300$ K, and $455.67$ $\mu$W K$^{-2}$ m$^{-1}$ at $600$ K. The thermoelectric properties predicted here can bring these thermoelectric oxides to applications at lower temperatures traditionally fulfilled by more toxic and otherwise burdensome materials.