Jae Soo Shin

X-ray photoelectron spectroscopy study in Bi2Sr2Ca1-xNdxCu2O8+d

X-ray photoelectron spectroscopy (XPS) measurements were performed in Bi2Sr2Ca1-xNdxCu2O8+d (0≤x≤1) in order to investigate the change in the electronic states through the decrease of the holes in this system. The negative chemical shifts of the Cu 2p main peaks were observed, while their satellites did not shift but decreased in areas. These behaviors indicated that the holes at both Cu and O sites decrease with increasing Nd concentration x.

EFFECT OF NI SUBSTITUTION FOR CU IN 110 K PHASE OF (BI, PB)-SR-CA-CU-O SUPERCONDUCTORS

The effect of Ni substitution for Cu in the 110 K phase of (Bi, Pb)-Sr-Ca-Cu-O superconductor was investigated. Samples of Bi1.84Pb0.34Sr1.91Ca2.03(Cu1-xNix)3.06Oy were prepared. The single phase was obtained up to a Ni concentration of x=0.015. The zero-resistance temperature Tc decreased monotonically in the region of x≤0.03 and became 90 K at x=0.03. Tc remained constant at 89 K in the region of 0.03<x≤0.10. Through X-ray photoelectron spectroscopy measurements, the Cu 2p core level was found to shift toward lower binding energy with the increase of x, which shows the Ni substitution for Cu.

Effect of Y substitution for the Ca site in the 110 K phase of (Bi, Pb)-Sr-Ca-Cu-O superconductors

The effect of the substitution of the trivalent Y ions for the divalent Ca ions has been studied in the 110 K phase of Bi1.84Pb0.34Sr1.91(Ca1-xYx)2.03Cu3.06O10+y (x=0~0.05). We found the solubility limit of Y to the 110 K phase around x=0.015. Within the solubility limit, the c-axis seemed to decrease with increasing x. In the region of the 110 K single phase, the critical temperature Tc gradually decreased with the increase of x, corresponding to the decrease of the carrier concentration.

Effect of Y Substitution for Ca in Bi2Sr2CaCu2O8+d Superconducting Films Prepared by Liquid Phase Epitaxial Method

The effect of Y substitution for Ca on superconducting properties has been investigated in Bi2Sr2CaCu2O8+d films prepared by liquid phase epitaxial method. The Y concentration in the film, xS, increased in proportion to that in the solution, xL, in the region of 0≤xL≤0.2, and then it was saturated. The incorporation ratio of Y in solid and in liquid, xS/xL, for 0≤xL≤0.2 was found to be about 3. The xS dependences of the zero-resistance temperature and the carrier concentration showed that about half of the Y concentration incorporated in the films contributes to the effect of the Y substitution obtained in sintered materials.

XPS Study on the Formation Process of the High-Tc Phase in the Bi-Pb-Sr-Ca-Cu-O System

X-ray photoemission spectroscopy (XPS) measurements were carried out to investigate the changes in the Cu ion valency through the formation of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O superconducting system. The Cu2+ composition increased rapidly in the initial stages of sintering and became saturated, whereas the Cu+ and Cu3+ compositions showed a systematic change, within a certain sintering time, dependent on the sintering temperature. It was found that these changes in the Cu ion valency reflect the structural change in the formation of the high-Tc phase in this system.

XPS measurements in Bi2Sr2Ca1−xYxCu2O8+d

We performed X-ray photoemission spectroscopy (XPS) measurements in Bi 2 Sr 2 Ca 1−x Y x Cu 2 O 8+d system in order to investigate the relation between the Cu valence and superconductivity. The negative chemical shift of the Cu 2p spectra indicated that holes in the Cu site decreased with increasing Y concentration. The change in the shape and the positive chemical shift of the O 1s spectra indicated that holes on the oxygen site in Cu-O layer increased with increasing Y concentration. The superconducting transition temperature decreased monotonically with decreasing the Cu valence and vanished when the Cu valence became less than 2.

X-ray photoemission spectroscopy study on Bi2Sr2-x Ca1+x Cu2O8+d

Abstract We have elucidated the distribution of the Sr and Ca atoms in the Bi2Sr2-x Ca1+x Cu2O8+d system (0  ′  0.8) by X-ray photoemission spectroscopy (XPS). The carrier concentration and the superconducting temperature Tc have a maximum at x = 0.2 and then monotonously decrease with increasing x. From the XPS measurements, the Sr3d and Ca2p spectra are found to be decomposed into two states. We have clarified the occupation of the Sr and Ca atoms in the Sr-and Ca-layers and found that the deficiency in the Sr-layer has a great influence on superconductivity.

Preparation of Bi-Sr-Ca-Cu-O superconducting films by the liquid phase epitaxial method

Bi-Sr-Ca-Cu-O superconducting films were prepared on MgO(100) single-crystal substrates by the liquid phase epitaxial (LPE) method using Bi 2 Sr 2 CaCu 2 O x solution. X-ray diffraction measurements and scanning electron microscopy analyses revealed that films were predominantly oriented with the c -axis perpendicular to the substrate surfaces. The as-grown film consisted of the 10 K and 80 K phases. After the post-annealing, films mainly consisted of the 80 K phase.

Formation of Bi2212 Phase via Bi2201 Phase in Liquid-Phase Epitaxial Growth

Bi2212 single-phase films are prepared using the liquid-phase epitaxial (LPE) method. The dependence of the relative content of the Bi2212 phase in the as-grown films on the growth temperature has made it clear that the Bi2212 phase can be obtained in a narrow temperature region around 980°C. LPE growth under the liquid-temperature gradient is examined. It is found that the temperature gradient suppresses the growth of the Bi2212 phase.

Effect of the Bi2201 coexistence on the Bi2212 solidification in the LPE film

The solidification of the Bi2212 phase has been investigated by using the LPE method. The dependence of the relative content of the Bi2212 phase in the as-grown film on the growth temperature has made it clear that the Bi2212 phase can be obtained only from a temperature near 980°C. It has suggested that the narrow solid phase of the Bi2212 phase adjoins to the liquid phase of the Bi2201 phase.