Thermoelectric Power of TCNQ-Treated (Bi,Pb)-2223 Cuprates

Abstract

According to powder X-ray and TEM analyses, bulk 2a×2b×c superstructure of TCNQ-treated (Bi,Pb)-2223 cuprates has been attributed to an ordering of oxygen vacancies in the covalent CuO2 layers and also likely in the ionic SrO layers. The transport behavior of both electrical resistivity and thermoelectric power for the (Bi,Pb)-2223 cuprate undergoes a dramatical change after TCNQ treatment. The conductivity of this material shows a metal-like temperature dependence with high resistivity (102 ~ 103 Ω-cm), and a relatively rapid resistivity drop at ca. 11.7 K. These facts indicate that hole carrier concentration in the CuO2 layers is significantly reduced. The thermoelectric power exhibits a metallic-diffusion behavior, which is similar to that of the c-axis in Bi-2212 single crystals. The disappearance of peak thermoelectric power of this material suggests that the commonly observed peak behavior in cuprate superconductors is associated with the hole carriers in the CuO2 layers. In the framework of Kaiser’s metallic-diffusion thermoelectric power model, it seems that the abnormally large electron-phonon enhancement effect of thermoelectric power arising from the CuO2 layers of the pristine (Bi,Pb)-2223 cuprate is significantly reduced in the TCNQ-treated samples with the 2a×2b×c superstructure. This could be due to a low carrier concentration as a result of oxygen vacancies in the CuO2 layers.