X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY OF IMPURITIES AMONG HIGH-TEMPERATURE SUPERCONDUCTIVE OXIDE BI2SR2CAN-1CUNOY(N=1,2)

The impurities among high-temperature superconductive oxide, Bi2Sr2Can-1CunOy (n = 1, 2), were studied by XPS; these impurities could not be detected by the X-ray diffraction method. When blocks of the superconductive oxide were fractured, various planes appeared. Those planes having river patters, which seemed to be cleaved surfaces of single crystals, were selected for XPS studies. The spectral patterns were classified into three groups. The spectra of group (A) were due to the clean cleaved surfaces of single crystals of Bi2Sr2CuO6+x or Bi2Sr2CaCu2O8+x'. The spectra of groups (B) and (C) indicated that the impurities covered the planes of the single crystals. Curve fitting of the Sr 3d and Ca 2p levels showed that the chemical species of Sr and Ca were carbonates in (B), and carbonates and undefined species having high ionic bonding in (C). The dissolution of a sample into a MnNO3/HNO3 solution first gave a purple color due to MnO4- at some parts of the sample; the color finally disappeared. The other dissolution into a Fe3+ solution gave Fe2+ ions, which were determined by Cr2O72- ions. These chemical reactions and the spectra of the Cu 2p and Bi 4f levels of group (C) indicate that copper and bismuth are Cu(I) and Bi(V), respectively.