Influence of Bi Substitution with Rare-Earth Elements on the Transport Properties of BiCuSeO Oxyselenides

: 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 μV K –1 to 238 μV K –1 at 800 K. Thus, a power factor of nearly 3 μW cm –1 K –2 is achieved for Bi 0.92 R 0.08 CuSeO 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 originated from atomic mass fluctuations between R and Bi. Ultimately, a maximum z T 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.