Jia Yunbo

Growth of Bi2Sr2CaCu2O8 single crystals from Bi-rich melts

Abstract High-quality Bi 2 Sr 2 CaCu 2 O 8 single crystals with dimensions up to 15x4x0.05 mm 3 were grown from the starting composition Bi 2+ x Sr 2 CaCu 2 O y , where x =0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7. Different amounts of Bi 2 O 3 in excess are included in each crystal growth run to act as flux for the growth and the optimum concentrations of the flux amount have been found. Structure characterization of a high-quality 2212 free crystal of 5x1.8x0.02 mm 3 was conducted by the (00 l ), ( h 00) and (0 k 0) X-ray diffractions, using a rotating anode diffractometer, and the back-reflection Laue photograph. It is found that melting incongruency is the main problem encountered in the growth of large and pure-phase single crystals from Bi 2 O 3 -rich melts and we have shown that, for x =0.8, crystals of 2212 phase and crystals of 2201 phase coexisting with CuO are obtained from the two segregated parts of the Bi-rich melts.

Observation of the modulated structure in Bi2Sr2CaCu2Oy single crystals by using an X-ray rotating-anode diffractometer

Abstract With a conventional X-ray rotating-anode diffractometer, structure characterization of a pure and highly oriented Bi 2 Sr 2 CaCu 2 O y single crystal sheet with large dimensions of 5×1.8×0.03 mm 3 has been conducted. Incommensurate satellites corresponding to a modulation 0.21 b ∗ + c ∗ have been observed up to second order. Apart from the asymmetry in intensities of the symmetrically located satellites, we revealed one more characteristic of the modulated structure, that the satellites are stretched along the c ∗ direction to form poles in reciprocal space. The technique used is suggested to be convenient and practical for studies concerning especially the modulations for large crystals.

Structural Characteristics of 2212-Phase Single Crystal in the Bi-Sr-Ca-Cu-O Superconductor

A single crystal of Bi-Sr-Ca-Cu-O 2212 superconducting phase has been studied by combining the Laue method with the method of X-ray diffractometry. It is suggested that the single-crystal structure of a superconductor is a modulated structure of a three-dimensional period coexisting with a two-dimensional lattice. In the structure, the Bi-concentrated bands, which form a three-dimensional modulated structure that corresponds to the results observed in high-resolution electron microscopy, do not entirely enter the parent structure lattice, but divide the parent structure into oxygen-deficient pervoskitelike layers. The pervoskitelike layer has a quasi-two-dimensional structure. The element modulation of Sr and Ca appears in the two-dimensional lattice, which is caused by the effect of Bi-concentrated bands. Meanwhile, the superlattice is formed on the ab plane. The three-dimensional structure of periodic modulation is formed by the pervoskitelike layer and Bi-concentrated band as a unit.

Study on the crystal and electronic structure of ceramics

(PrBCO) is unique in the ( R = rare earth) series because it is not superconducting. In fact, for , drops monotonically with Pr concentration, with going to zero at 55% Pr. There have been many studies of this material with the hope that an explanation for the lack of superconductivity in PrBCO might help explain why is superconducting. Unfortunately, to date, none of the proposed explanations has been totally satisfactory and without objection due to the considerable controversy of the results obtained by different experiments. In this paper, a series of samples of (YPrBCO) have been studied by x-ray diffraction, Raman spectroscopy and XPS. The results reveal that the Pr dopant does not change the orthorhombic symmetry of the samples. The peak positions at 502 and of the Raman spectra become shifted for different Pr concentration, which suggests a change in oxygen content upon substitution of Pr ion for Y ion. There are two valences of Pr ions in YPrBCO. The valence of Pr is changed with change in Pr content x. The relative content of and is closely related to the total Pr content x. The valence of Pr is close to 3+ for small x, and is increased as x increases. The valence change of the Pr ion would directly result in the increase of oxygen content. A ligand hole localized on the Pr-O(2)/O(3) band would remove a hole from the conduction band and yield a formal site. The strong hybridization between Pr 4f electrons and conduction holes in the planes induces a localization of mobile holes causing the suppression of superconductivity in the YPrBCO system. In addition, the existence of some extra oxygen atoms around Pr will also affect the distortion of the planes and possibly assist in the suppression of the superconductivity.

The study of structural characteristics of YBaCuO superconducting thin films on (001) Zr(Y)O2 by x‐ray diffraction

Three kinds of x‐ray diffraction experiment of YBa2Cu3O7−x thin film on Zr(Y)O2 have been carried out. It has been proved that YBaCuO superconducting thin film grow epitaxially on (001) Zr(Y)O2. The orientation relationships between YBaCuO thin film and Zr(Y)O2 substrate are (001) YBaCuO∥(001) ZrO2 and [100] YBaCu∥[110] Zr(Y)O2.

Synthesis and structure of Sr2(YCe)nCuFeOy (n=2, 3, 4), a new series of layered cuprates with flourite layers

Abstract A new series of cuprates Sr 2 (YCe) n CuFeO y ( n =2, 3, 4) was synthesized and investigated by XRPD and TEM. Sr 2 Y 1.34 Ce 0.66 CuFeO y ( n =2) and Sr 2 Y 1.4 Ce 1.6 CuFeO y ( n =3) were prepared by solid reaction method and sol-gel process, respectively. The crystal structure of Sr 2 (YCe) n CuFeO y ( n >2) was found to be a layered structure with multiple flourite blocks.

Effect of Oxygen-Diffusion Possibly Involved in Perovskite Unit on Superconductivity of Various Oxygen-Doped Bi2Sr2CaCu2O8+y Single Crystals

For a highly oriented Bi2Sr2CaCu2O8+y single crystal with a lower as-grown Tc of 72K, on airannealing at 250°C for 2 h, its Tc remained unchanged, while increased to 83K after annealing for 25 h. For another crystal with a higher as-grown Tc of 86.7K and annealed under the same condition, its Tc was unchanged except for a slight improvement of ΔTc and was independent of the annealing time. X-ray diffraction showed that there were no changes of c-axis lattice parameter for the annealed crystals. If the above two crystals, after annealing at 250°C for 25 h, were further annealed at 600°C for 20 h, then Tc was increased to the same value of almost 88K and the c-axis lattice parameter showed a dramatic contraction. We suggested that the improvement of superconductivity of the sample annealed at much lower annealing temperature (250°C) are associated with the oxygen diffusion involved in the pervoskite unit and this diffusion from the perovskite unit occurs earlier than that from Bi-O layers.

Lattice matching of GdBa2Cu3O7-x superconducting thin films on Zr(Y)O2

GdBa2Cu3O7-x superconducting thin films, which were grown in situ on a (001) Zr(Y)O2 substrate by DC magnetron sputtering with zero resistance transition temperature Tc in the range 89.6-92.18 K, have been studied by X-ray diffraction experiments and pole figures. The relation between the a and b axes of GdBa2Cu3O7-x thin films and the in-plane lattice vectors of Zr(Y)O2 has been obtained from the pole figures. It is found that there are two sorts of twins, 45 degrees and 90 degrees .

The comparison of structural characteristics between 2212 and 2201 phases in the Bi-Sr-Ca-Cu-O system

Abstract The Laue and Bragg diffraction patterns of a Bi-based 2212-phase (Bi 2 Sr 2 CaCu 2 O y ) single crystal have been investigated by Laue photography using continuous radiation and monochromatic radiation, and compared with those of a Bi-based 2201-phase (Bi 2 Sr 2 CuO z ) single crystal. It is found that there are a two-dimensional lattice and a three-dimensional lattice in the Bi-based 2212-phase crystal, which are structurally independent of each other. However, there is only a three-dimensional superlattice in the Bi-based 2201-phase crystal. Combining these results with the reported results of high-resolution electron microscope research, it is suggested that “Bi-concentrated” bands of the Bi-based 2201 phase have entirely entered into the lattice of the parent structure formed by CaCuO 2 [1], but not of the Bi-based 2212 phase, in which the “Bi-concentrated” band formed a lattice itself.

The structural characteristics of Bi-based 2212 phase whiskers

Abstract We have succeeded in studying the structural characteristics of a single thread of Bi-based 2212-phase whisker by X-ray diffraction. It is found that the structural characteristics of a single thread of whisker coincide with those of a 2212-phase single crystal. The single thread of whisker is a 2212 plate-like single crystal and is stacked in a layered structure. There are a number of low-angle boundaries in the BC-plane, but few in the AB-plane of the whisker.