Phonon Scattering and Suppression of Bipolar Effect in MgO/VO2 Nanoparticle Dispersed p-Type Bi0.5Sb1.5Te3 Composites.

Song Yi Back,Hyunyong Cho,Jae Hyun Yun,Jong-Soo Rhyee,Gareoung Kim

doi:10.3390/ma14102506

Abstract

Bismuth-Telluride-based compounds are unique materials for thermoelectric cooling applications. Because Bi2Te3 is a narrow gap semiconductor, the bipolar diffusion effect is a critical issue to enhance thermoelectric performance. Here, we report the significant reduction of thermal conductivity by decreasing lattice and bipolar thermal conductivity in extrinsic phase mixing of MgO and VO2 nanoparticles in Bi0.5Sb1.5Te3 (BST) bulk matrix. When we separate the thermal conductivity by electronic , lattice , and bipolar thermal conductivities, all the contributions in thermal conductivities are decreased with increasing the concentration of oxide particle distribution, indicating the effective phonon scattering with an asymmetric scattering of carriers. The reduction of thermal conductivity affects the improvement of the ZT values. Even though significant carrier filtering effect is not observed in the oxide bulk composites due to micro-meter size agglomeration of particles, the interface between oxide and bulk matrix scatters carriers giving rise to the increase of the Seebeck coefficient and electrical resistivity. Therefore, we suggest the extrinsic phase mixing of nanoparticles decreases lattice and bipolar thermal conductivity, resulting in the enhancement of thermoelectric performance over a wide temperature range.

Highlights

IntroductionThe TE efficiency is defined by the dimensionless figure-of-merit, ZT = S2 T/(κρ), where S, T, ρ, and κ are the Seebeck coefficient, absolute temperature, electrical resistivity, and thermal conductivity, respectively
When we calculated the bipolar thermal conductivity from the above equations, we found a reduction of bipolar thermal conductivity in the oxide composites, but the lattice thermal conductivity showed a negative value at high temperatures, indicating the overestimation of bipolar thermal conductivity
We investigated the thermoelectric properties of MgO/VO2 BST composites by extrinsic phase mixing of MgO and VO2 nanoparticles in the BST matrix

Summary

Introduction

The TE efficiency is defined by the dimensionless figure-of-merit, ZT = S2 T/(κρ), where S, T, ρ, and κ are the Seebeck coefficient, absolute temperature, electrical resistivity, and thermal conductivity, respectively. A high TE performance is required for a high power-factor, PF = S2 /ρ, and a lower thermal conductivity. The nano-structuring [7,8] and secondary phase dispersion [9,10] can induce pronounced phonon scattering, which results in the reduction of thermal conductivity. The anharmonic lattice vibration leads to the intrinsic low lattice thermal conductivity [11,12]. There have been investigations on the high power-factor and low thermal conductivity through the Peierls distortion [13,14] and selective charge Anderson localization [15]

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Results

Conclusion