Transport properties and electronic states in the layered thermoelectric rhodate (Bi_1-xPb_x)_1.8Ba₂Rh _1.9O_y

Resistivity, thermopower and Hall coefficient have been systematically measured for polycrystalline samples of (Bi_1-xPb_x) _1.8Ba₂Rh_1.9O_y. An upturn of the resistivity and the Hall coefficient below 50 K is ascribed to decrease in the density of states due to a pseudogap formation. The thermopower and Hall coefficient are nearly identical to those of the thermoelectric oxide Bi ₂Sr₂Co₂O_y. This suggests a nearly identical density of states between the two oxides, which is also verified from a first-principle calculation, where a broader 4d orbital and a larger rhodium-rhodium distance along the in-plane direction accidentally give nearly the same density of states as those of the layered cobalt oxides.