Cu valence states in superconducting BiPbSrCaCuO system

Abstract

The oxidation states of Bi, Pb, and Cu in the BiPbSrCaCuO (BPSCCO) system have been determined by a combination of volumetric measurement technique and iodometric titration. It was found that, in contrast to previous reports, the concentration of the Cu 3+ ions decreased with increasing Pb content, and Cu 3+ ions were absent in samples of Bi 1.6Pb 0.4Sr 1.6Ca 2Cu 3O 9.8, while a T c at 108 K and a J c of greater than 12,000 A/cm 2 at 77 K were observed. The 110 K phase in BPSCCO was stabilized and showed a high tolerance to change in oxygen partial pressure during sintering. In Pb-doped materials, Bi appears to be trivalent while Pb was determined to be mixed-valence Pb 4+ Pb 2+ . It is suggested that superconductivity in BPSCCO may result from a dynamic transfer of holes from Bi PbO layers toward CuO 2 planes.