XANES Study on the Generation and Distribution of Holes via Ca Substitution and O Doping in Cu(Ba0.8Sr0.2)2(Yb1−xCax)Cu2O6+z

✍ Scribed by M. Karppinen; H. Yamauchi; T. Nakane; K. Fujinami; K. Lehmus; P. Nachimuthu; R.S. Liu; J.M. Chen

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 277 KB
• Volume: 166
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2002.9588

✦ Synopsis

Generation of holes is facilitated in the Cu(Ba 0.8 Sr 0.2 ) 2 (Yb 1Àx Ca x )Cu 2 O 6+z (Cu-1212) system by two independent ways, i.e., by Ca substitution (0rxr0:35) and O doping (0ozo1). The distribution of holes between the CuO 2 -(Yb 1Àx Ca x )-CuO 2 block containing two identical superconductive CuO 2 planes and the ''charge-reservoir'' block consisting of a single CuO z chain has been quantitatively investigated by means of O K-edge and Cu L 2,3 -edge X-ray absorption nearedge structure (XANES) spectroscopy. The resultant values for the CuO 2 -plane hole concentration are compared with those calculated employing the bond-valence-sum (BVS) method from the neutron powder diffraction (NPD) data previously reported for the same samples. The results of the two methods are in good agreement. The two independent hole-doping ways are found to result in different distributions of holes over the crystal, i.e., different ratios of hole numbers at the CuO 2 plane and the CuO z chain. With Ca substitution holes are directed efficiently into the CuO 2 plane, while for O doping holes are more homogeneously distributed between the CuO 2 plane and the CuO z chain. Moreover, the value of T c at a fixed CuO 2 -plane hole concentration is shown to be higher for Ca-substituted than for O-doped samples.