Thermoelectric properties of Bi2O2Se single crystals

TL;DR

This study investigates the thermoelectric properties of Bi2O2Se single crystals, revealing high electron mobility, low thermal conductivity, and improved figure of merit compared to polycrystals, attributed to strong phonon scattering.

Contribution

First comprehensive analysis of thermoelectric properties of Bi2O2Se single crystals, highlighting enhanced performance and underlying phonon scattering mechanisms.

Findings

Electron mobility up to 250 cm²V⁻¹s⁻¹

Thermal conductivity as low as 2 W/m·K

Figure of merit of 0.188 at 390 K

Abstract

Bismuth oxyselenide (Bi$_2$O$_2$Se) attracts great interest as a potential n-type complement to p-type thermoelectric oxides in practical applications. Previous investigations were generally focused on polycrystals. Here, we performed a study on the thermoelectric properties of Bi$_2$O$_2$Se single crystals. Our samples exhibit electron mobility as high as 250 cm$^2.$V$^{-1}$.s$^{-1}$ and thermal conductivity as low as $2$ W.m$^{-1}$.K$^{-1}$ near room temperature. The maximized figure of merit is yielded to be 0.188 at 390 K, higher than that of polycrystals. Consequently, a rough estimation of the phonon mean free path ($\ell_\textrm{ph}$) from the kinetic model amounts to 12 $\r{A}$ at 390 K and follows a $T^{-1}$ behavior. An extrapolation of $\ell_\textrm{ph}$ to higher temperatures indicates that this system approaches the Ioffe-Regel limit at about 1100 K. In light of the phonon dispersions, we argue that the ultralow $\ell_\textrm{ph}$ is attributed to intense anharmonic phonon-phonon scattering, including Umklapp process and acoustic to optical phonon scattering. Our results suggest that single crystals provide a further improvement of thermoelectric performance of Bi$_2$O$_2$Se.