Grain Boundary Interfaces Controlled by Reduced Graphene Oxide in Nonstoichiometric SrTiO3-\u03b4 Thermoelectrics

Jamil Ur Rahman,Kyu Hyoung Lee,Nguyen Van Du,Won-Seon Seo,Woo Hyun Nam,Soonil Lee,Weon Ho Shin,Myong Ho Kim

doi:10.1038/s41598-019-45162-7

Abstract

Point defect or doping in Strontium titanium oxide (STO) largely determines the thermoelectric (TE) properties. So far, insufficient knowledge exists on the impact of double Schottky barrier on the TE performance. Herein, we report a drastic effect of double Schottky barrier on the TE performance in undoped STO. It demonstrates that incorporation of Reduced Graphene Oxide (RGO) into undoped STO weakens the double Schottky barrier and thereby results in a simultaneous increase in both carrier concentration and mobility of undoped STO. The enhanced mobility exhibits single crystal-like behavior. This increase in the carrier concentration and mobility boosts the electrical conductivity and power factor of undoped STO, which is attributed to the reduction of the double Schottky barrier height and/or the band alignment of STO and RGO that allow the charge transfer through the interface at grain boundaries. Furthermore, this STO/RGO interface also enhances the phonon scattering, which results in low thermal conductivity. This strategy significantly increases the ratio of σ/κ, resulting in an enhancement in ZT as compared with pure undoped STO. This study opens a new window to optimize the TE properties of many candidate materials.

Highlights

In recent years, strontium titanium oxide (STO) is considered an interesting n-type material in thermoelectric research due to its high absolute Seebeck coefficient[9]
We propose a novel strategy to achieve enhanced transport properties with the improved thermoelectric performance of undoped Strontium titanium oxide (STO) by fabricating its composite with reduced graphene oxide (RGO)
No agglomeration of RGO ≤ 0.7 wt% could be observed in the scanning electron microscopy (SEM) micrographs, indicating that undoped STO grains well interacted with RGO sheet

Summary

Introduction

Strontium titanium oxide (STO) is considered an interesting n-type material in thermoelectric research due to its high absolute Seebeck coefficient[9]. The deterioration of the double Schottky barrier would change the electronic transport properties at atomic-scale[26] To demonstrate this issue, we propose a novel strategy to achieve enhanced transport properties with the improved thermoelectric performance of undoped STO by fabricating its composite with reduced graphene oxide (RGO). We demonstrate a promising preparation approach to fabricate STO/RGO composite free from the double Schottky barrier Most importantly, by this strategy even in the undoped polycrystalline STO can provide single crystal-like charge transport properties with high electrical conductivity and power factor. By this strategy even in the undoped polycrystalline STO can provide single crystal-like charge transport properties with high electrical conductivity and power factor This approach provides the opportunity to suppress the phonon transport at the STO/RGO interface

Methods

Results

Conclusion