Redox mechanisms and density of holes by XAS in the compensated series Bi2-xPbxSr2Ca1-xYxCu2O8+δ ( 0 ≤ x ≤ 1)

Bi2-xPbxSr2Ca1-xYxCu2O8+δ (0 ≤ x ≤ 1) of structural type Bi(2212) is a very interesting solid solution since one is able to adjust the critical temperature over a large range of x by means of a mere formal exchange of charge between cations which do not belong to the essential [CuO2]∞ planes. X-ray absorption spectroscopy was performed at bismuth, lead, and copper L3-edges on the Bi2-xPbxSr2Ca1-xYxCu2O8+δ (0 ≤ x ≤ 1) solid solution in order to investigate the formal valence states of the elements and the correlation between hole density on the [CuO2]∞ planes and superconducting properties. It is shown that lead substitution does affect the role of the [BiO]∞ planes which exchange electrons (holes) with the [CuO2]∞ planes. The decrease of the hole density in the [CuO2]∞ planes with increasing x has been correlated to the decrease of Tc's, whereas the rapid decrease of the diamagnetic volume for 0.3 ≤ x ≤ 0.7 has been understood on the basis of a segregation between bismuth- and lead-rich phases. 37 refs., 11 figs., 1 tab