Valence analysis of Pb and Cu and superconductivity of (Pb,Cu)(Sr,La) 2CuO y

Abstract

The Pb 1201 phases, Pb 0.5Cu 0.5Sr 2− x La x CuO y , with x = 1.0–1.2 and Pb 0.6Cu 0.4Sr 2− x La x CuO y , with x = 0.9–1.2 have been prepared at 1010–1015°C for 1.7–2.0 hours in flowing oxygen. To evaluate the Cu valence in the CuO 2 sheet, the Pb valence is separately determined by K 2Cr 2O 7 titration, in addition to the oxygen content determination by iodometry. The T c (onset) rises as the oxygen content decreases due to release of the overdoping, but was not affected by La 3+ substitution for Sr 2+ and by the Pb content in the (Pb,Cu)O layer. The explanation is that the Cu valence in the CuO 2 sheet decreases as the oxygen content decreases, while the Pb valence is reduced by La 3+ substitution or the Pb content increases.