The normal state resistivity and thermopower of a series of lead-substituted n = 2 BSCCO superconductors

Abstract

We have prepared a series of eight polycrystalline samples of lead-substituted compounds of the n = 2 member of the BSCCO superconducting series Bi2-xPbxSr2Can-1CunO2n+4-δ; more specifically in our case of initial stoichiometry Bi2.1-xPbxSr2Ca0.9Cu2O8-δ, with x ranging from 0.0 to 0.35. The transport properties resistivity of all eight and thermoelectric power of six of the eight of these samples have been measured over the temperature range 80-300K. The measurements were performed by the differential method in a self-consistent manner with data being logged and analysed semi-automatically by computer in control of a GPIB bus. We find that increasing substitution of bismuth by lead in the above compound tends to improve the quality and also increases the metallic nature of the measured transport properties. The linear behaviour above Tc of the thermopower with temperature data reported by other authors has also been observed in all the samples we were able to complete measurements on; the resistivity data is typical of that seen for the high Tc oxide superconductors, being metal-like and linear above Tc for most samples although the magnitude may be slightly higher than other reports have stated. The magnitude of the thermopower is typically metallic, ranging from about 1-10 μV/K over our temperature range for all samples. The sign of the thermopower is positive, suggesting conduction by holes. The slope of the linear portion of the data is negative with typical magnitude ~.01μV/K2 For some samples the thermopower goes through zero to become negative at the higher temperatures and this would appear to be the case for all our samples were the upper temperature limit to be extended to say 400K.