X-ray absorption near-edge structure study of Bi 2Àx Pb x Sr 2 (Sm 0.85 Ce 0.15 ) 2 Cu 2 O 10+y G. Liang * , Q. Yao, S. Zhou, D. Katz Department of Physics, Sam Houston State University, Huntsville, TX 77341, USA Received 5 April 2002 Available online 24 June 2005 Abstract Near-edge X-ray absorption spectroscopy results of Ce L 3 -, Pb L 3 -, Bi L 3 -, and Cu K-edge for Bi 2Àx Pb x Sr 2 (Sm 0.85 - Ce 0.15 ) 2 Cu 2 O 10+y (0 6 x 6 1) series are presented. Ce in this series is found to be in a valence state similar to that in CeO 2 . The lack of the 2p ! 6s transition feature in both the Bi and Pb L 3 -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 v K increases from 2.20 to 2.34, indicating that the substitution of Bi 3+ by Pb 2+ draws electronic charge out of the CuO 2 layers, increasing the oxygen hole concentration as well as the superconducting transition temperature T c . We also found that for 0.0 6 x 6 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. Ó 2005 Elsevier B.V. All rights reserved. PACS: 74.72.Hs; 78.70.Dm; 61.10.Lx; 71.70.Ch Keywords: High-T c superconductors; XANES; Valence; Edge energy; Cu K-edge 1. Introduction In the big family of high-T c oxide supercon- ductors there exist several superconducting cup- rate systems containing the same fluorite-like (R,Ce) 2 O 2 layers where R is the rare earth ele- ments [1–3]. These fluorite-like layers play impor- tant roles in stabilizing the crystal structure and in regulating the charge carrier density in the conducting CuO 2 layers in these materials. The Bi 2 Sr 2 (R,Ce) 2 Cu 2 O 10+y (the so called Bi-2222) compound, originally discovered by Tokura et al. [2], is a compound with such fluorite-like layers. This compound has a ‘‘double sandwich’’ structure: 0921-4534/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2005.05.011 * Corresponding author. Tel.: +1 936 294 1608; fax: +1 936 294 1585. E-mail address: phy_gnl@shsu.edu (G. Liang). Physica C 424 (2005) 107–115 www.elsevier.com/locate/physc