Effect of praseodymium and lanthanum substitution for bismuth on the thermoelectric properties of BiCuSeO oxyselenides

The results of investigating the thermoelectric properties of the bulk $р$-type oxyselenides Bi$_{1-x}$Pr$_{x}$CuSeO ($x$ = 0, 0.04, 0.08) and Bi$_{0.96}$La$_{0.04}$CuSeO obtained by the solid-state reaction technique are presented. The temperature dependences of the thermopower, electrical resistivity, and thermal conductivity are measured at temperatures from room temperature to 800 K. Over the whole temperature range, a decrease in the electrical resistivity and thermopower is observed with increasing substitution level, while the thermal conductivity is almost unaffected by the substitution of rare-earth elements for bismuth. Despite the nominal valence of Bi, La, and Pr being the same, the replacement of bismuth by rare-earth ions leads to an increase in the charge-carrier concentration, which may be caused by a difference in the electronic configurations of ions, resulting in a shift of the Fermi level to the valence band.