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

Abstract

In this study, we demonstrate that introduction 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 Bi3+ to R3+ substitution, the electronic transport properties are significantly improved in a broad temperature range from 100 to 800 K. In particular, the electrical resistivity decreases by 2 times, while the Seebeck coefficient drops from 323 to 238 μV K-1 at 800 K. Thus, a power factor of nearly 3 μW cm-1 K-2 is achieved for Bi0.92R0.08CuSeO samples 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 originating from atomic mass fluctuations between R and Bi. Ultimately, a maximum zT value of nearly 0.34 at 800 K is obtained for the Bi0.92La0.08CuSeO sample, which is ∼30% higher than that of pristine BiCuSeO.