Wataru Futo

The preparation conditions and characteristics of the Bi−Sr−Ca−Cu−O single crystals

The 7 K, (7+80) K and 80 K phase lli-Sr-Ca-Cu-O single crystals were prepared by changing the composition of the starting materials using a self-flux method. The results of AES (Auger electron spectroscopy) measurements indicate that a part of the Sr would be substituted by Ca in the 7 K phase crystal. Plate-like crystals were observed by SEM (scanning electron microscope) in the as-grown 80 K phase crystal surface. This may be due to the fact that the specimen has a layer structure.

XPS Studies of Bi-Sr-Ca-Cu-O Single Crystal and Ceramics Surfaces

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.

XPS Studies of 80 K-Phase Bi-Sr-Ca-Cu-O Single Crystals

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 Surface Characterizations of 80K-Phase Bi(Pb)-Sr-Ca-Cu-O Bulk Single Crystals and Thin Films

The 80K-phase Bi-system superconducting bulk single crystals and thin films were studied by SEM, LEED, RHEED, AES, XPS and SAM. The clean surfaces of the bulk single crystals were obtained by cleaving them in ultra-high vacuum or heating in vacuum after cleaving in air. The LEED and RHEED patterns from the clean surfaces showed ~ 1 × 5 structures. By comparing the results of AES, XPS and SAM from the film surfaces with those from the bulk single crystals, we found that the surfaces of thin films were covered with the impurities formed by post-annealing.

Preparation Conditions of 80K-Phase Bi (Pb)-Sr-Ca-Cu-O Single Crystals

The 80K-phase Bi(Pb)-Sr-Ca-Cu-O single crystals were prepared by the self-flux method, and the optimum composition of the starting material, which was (Bi, Pb):(Sr, Ca):Cu=1:1:1, Ca/Sr=1 and Pb/(Bi+Pb)=0.15, was clarified. The prepared single crystals were plate-like and their typical sizes were 7 × 7 mm2. The critical temperature (Tc) of the specimen was ~ 74K.

X-Ray Photoelectron Spectroscopy Studies of 7 K-Phase Bi-System Single Crystals

The Bi-system single crystals with c-axis unit cell length of ~24 A, 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.