X-ray absorption near-edge structure study of Bi2−xPbxSr2(Sm0.85Ce0.15)2Cu2O10+y

Near-edge X-ray absorption spectroscopy results of Ce L3-, Pb L3-, Bi L3-, and Cu K-edge for Bi2−xPbxSr2(Sm0.85Ce0.15)2Cu2O10+y (0 ⩽ x ⩽ 1) series are presented. Ce in this series is found to be in a valence state similar to that in CeO2. The lack of the 2p → 6s transition feature in both the Bi and Pb L3-edge spectra indicates that Bi and Pb have valence values close to +3 and +2, respectively. With the Pb substitution level x increasing from 0.0 to 0.6, the Cu valence vK increases from 2.20 to 2.34, indicating that the substitution of Bi3+ by Pb2+ draws electronic charge out of the CuO2 layers, increasing the oxygen hole concentration as well as the superconducting transition temperature Tc. We also found that for 0.0 ⩽ x ⩽ 0.6, the Cu valence determined from mean characteristic energy of the Cu K-edge spectra is very close to the formal Cu valence estimated by charge neutrality consideration. The decrease of Cu valence with increase of x for samples with x > 0.6 could be due to the formation of a second phase in these samples.