STUDY OF CRYSTAL STRUCTURE AND PHYSICAL PROPERTIES OF THE COMPOUND Bi-Pb-Sr-Ca-Ba-Cu-O

Abstract

With the aid of transmission electron microscopy, the phenomenon of additional superstructure along [Formula: see text] direction was observed for a sample of Bi 1.7 Pb 0.3Sr2 Ca 1.8 Ba 0.2 Cu 3 O y, and two kinds of modulation mode along b axis was found to coexist in this sample. The images of SEM showed that the addition of Ba ions improved the property of two-dimensional growth. The results of XRD indicated that the substitution of Ba 2+ for Ca 2+ increased the volume fraction of the high-Tc phase (Tc>100 K). From the initial part of dc magnetization curve, it is estimated that about 36 percent of the sample volume is in the 110 K superconducting phase at 77 K. Its frozen magnetic flux density is about 8.6 G, which is 5–6 G higher than that of general Pb-doped sample, and its zero-resistance temperature can reach as high as 111 K. These changes of physical properties may be related to the adjustment of the microstructure.

Structural Modulation in Oxygen Deficient Epitaxial Bi2Sr2Ca1Cu2OX Observed by X-ray Reciprocal Space Mapping

“…Regarding the origin of the SC modulation, the intercalation of extra oxygen in a BiO layer has been studied in single crystals. [1][2][3][4] Aliovalent substitution was carried out using different cations, such as the partial substitution of La 3þ for Sr 2þ . 3,4) Taking the substitution of La 3þ for Sr 2þ for example, with increasing La 3þ doping, the SC modulation decreased along both the b-and c-axes, while the lattice constant b expanded and the c contracted.…”

“…[1][2][3][4] Aliovalent substitution was carried out using different cations, such as the partial substitution of La 3þ for Sr 2þ . 3,4) Taking the substitution of La 3þ for Sr 2þ for example, with increasing La 3þ doping, the SC modulation decreased along both the b-and c-axes, while the lattice constant b expanded and the c contracted. It is proposed that the expansion of the lattice constant b increases the mismatch between the BiO layer and perovskite blocks, thus the SC modulation is shortened.…”

Effect of oxygen pressure on structural modulation observed by X-ray reciprocal space mapping in epitaxial bismuth cuprate superconducting film

“…In order to investigate the origin of the SC structure, enormous effort is involved in the intercalation of extra oxygen in the Bi-O layer [4,[8][9][10]. The intercalation was carried out by aliovalent substitution such as the partial substitution of La 3+ for Sr 2+ , Pb 2+ for Bi 3+ [4,10], or 3d metals for Cu [11] etc. It is proposed that the SC periodicity was affected by internal strain caused by aliovalent substitution.…”

“…An aliovalent substitution results in lattice constants expanding along the c-axis and contracting along the b-axis while the SC structure simply changed along both b and c axes [10]. In ref.…”

“…In ref. [10], Zhiqiang et al proposed that the real driving force which results in modulation comes from a misfit degree between BiO and perovskite layers along the b-axis [10]. By re- placing ions with aliovalent ions, other effects such as inducing extra oxygen, might affect the SC structure on aliovalent substitution.…”