Influence of Bi substitution with rare-earth elements on the transport properties of BiCuSeO oxyselenides

TL;DR

This study shows that substituting rare-earth elements La or Pr into BiCuSeO enhances its thermoelectric performance by increasing charge carriers and reducing thermal conductivity, leading to a 30% improvement in zT at high temperatures.

Contribution

It is the first demonstration of how rare-earth substitution in BiCuSeO improves electronic and thermal transport properties for thermoelectric applications.

Findings

Electrical resistivity decreased by two times at 800 K.

Seebeck coefficient decreased from 323 to 238 μV/K at 800 K.

Maximum zT of 0.34 at 800 K for La-substituted sample.

Abstract

In this study, we demonstrate that introducing of rare-earth elements, $R$ = La or Pr, into the Bi-O charge reservoir layer of BiCuSeO leads to an increase of both, the charge carrier concentration and the effective mass. Although the charge carrier mobility slightly decreases upon Bi$^{3+}$ to $R^{3+}$ substitution, the electronic transport properties are significantly improved in a broad temperature range from 100 K to 800 K. In particular, the electrical resistivity decreases by two times, while the Seebeck coefficient drops from 323 ${\mu}$V K$^{-1}$ to 238 ${\mu}$V K$^{-1}$ at 800 K. Thus, a power factor of nearly 3 ${\mu}$W cm$^{-1}$ K$^{-2}$ is achieved for Bi$_{0.92}$La$_{0.08}$CuSeO sample at 800 K. Meanwhile, a noticeable decrease of the lattice thermal conductivity is observed for the substituted samples, which can be attributed to the enhanced point defect scattering mostly originated from atomic mass fluctuations between $R$ and Bi. Ultimately, a maximum $zT$ value of nearly 0.34 at 800 K is obtained for the Bi$_{0.92}$La$_{0.08}$CuSeO sample, which is ~30% higher than that of pristine BiCuSeO.