The XPS (X-ray photoelectron spectroscopy) measurements of the 80 K-phase Bi-Sr-Ca-Cu-O single crystals were carried out on surfaces obtained by cleaving in vacuum, by cleaving in air and heating in vacuum, and by Ar+-sputter etching of the air-cleaved-and-heated surface. The chemical bond natures of all the constituent elements from the air-cleaved-and-heated surface are approximately equal to those from the vacuum-cleaved surface. Sr and Ca from the sputtered surface are more oxidized than those from the vacuum-cleaved surface.

The XPS (X-ray photoelectron spectroscopy) spectra from (a) the cleaved surface of a single crystal, (b) the polished surface and (c) the Ar+-sputtered surface of the ceramics in Bi-Sr-Ca-Cu-O are mecnsured and compared. The chemical bond nature of Bi is the same in all three surfaces. Sr and Ca in (c) are more oxidized than those in (a). In (b), there are two kinds of Sr and Ca, one from a clean surface like the cleaved surface region, and the other, more oxidized Sr and Ca which exist in the Ar+-sputtered surface. Cu2+ is dominant in (a) and (b), while Cu+ is dominant in (c). The O 1s XPS spectrum from (c) is sharper and narrower than that from (a). This may be due to the existence of isolated metal oxides of Sr, Ca and Cu by Ar+-sputter etching.

The Bi-system single crystals with c-axis unit cell length of ∼24 Å, i.e., Bi-Sr-Cu-O (BSCO), Bi-Pb-Sr-Cu-O (BPSCO), Bi-Sr-Ca-Cu-O (BSCCO), and Bi-Pb-Sr-Ca-Cu-O (BPSCCO) single crystals, were prepared using the starting materials of various compositions by the self-flux method. X-ray photoelectron spectroscopy (XPS) measurements from the air-cleaved surfaces of the single crystals were carried out. From the results of the surface composition analyses, we found that Pb occupied a part of the Bi site in the BPSCO single crystal and Ca occupied a part of the Sr site in the BSCCO single crystal. The chemical bond natures of Sr, Cu and O in the BSCO crystal seem to be changed by doping with Pb and/or Ca.

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