Bi-based Single Crystals Research Articles

Re-growth of large Bi-2212 single crystals by a self-flux method

In order to obtain large size Bi 2Sr 2CaCu 2O x (Bi-2212) superconducting single crystals, we re-grew Bi-2212 single crystals by a self-flux method. In the first growth, Bi-based single crystals was grown by a self-flux method from the starting materials of Bi:Sr:Ca:Cu=2:2:1:2, which was the mixtures prepared from chemical powders of Bi 2O 3, SrCO 3, CaCO 3 and CuO. The mixture were put into the crucibles and heated at 960 °C for 10 h. They were slowly cooled down to 830 °C at the cooling rate of 1 °C/h. The size of the single crystal prepared in the first growth was 7×5 mm 2. In the second growth, the single crystals were again grown by a self-flux method using the single crystals prepared in the first growth. From the results, we found that the plate-like Bi-2212 single crystals with a size of 13.5×12 mm 2 were obtained. Therefore, the re-growth method is thought to be useful for obtaining large Bi-2212 single crystals.

Influence of oxygen content and structural defects on low-temperature mechanical properties of high-temperature superconducting single crystals and ceramics

The data for the microhardness and fracture toughness of Y–Ba–Cu–O and Bi-based single crystals and ceramics in the temperature range 77–293 K are presented and analyzed. Our study reveals that the microhardness of high temperature superconductors is very sensitive to the oxygen stoichiometry, the phase composition, the temperature, and to the microstructural defects such as impurities, intergranular boundaries, and voids. Attention is drawn to the anisotropy of the micromechanical properties and to the features of the fracture in the vicinity of the indentation. The data available on the plasticity of Y–Ba–Cu–O and Bi–Sr–Ca–Cu–O from micro- and macrotests are compared.

Growth of high quality BiSrCaCuO single crystals by the self-flux method with a temperature-holding process

We prepared the BiSrCaCuO(Bi-based) single crystals by the self-flux method with a temperature-holding process. The plate-like Bi-based single crystals with the size of about 2 x 2mm 2 were prepared at the holding temperature of 840°C. From the X-ray diffraction patterns, we found that the c-axis unit cell length of the crystal ( C 0=39 A ̊ ) was longer than that of an 80K phase Bi-based single crystal.

Middle-IR optical response and composition of Bi-based (2212)-type high-Tc superconductors

The optical response in the middle- and near-IR region has been examined in a sequence of Bi-based single crystals with various doping levels and phase compositions. The features in the optical spectra, which have been considered in the pseudodielectric function approximation, are used to characterize the free-carrier system in high-Tc compounds. A correlation between the chemical and phase composition, on the one hand, and the optical characteristics, on the other hand, has been analysed in Bi-based (2212)-type single crystals doped by Y(RE) ions.

Preparation and characterization of Bi-based single crystals of high T c superconductors

The discovery of B i S r C a C u O oxide superconductors has attracted considerable attention because their superconducting transition temperatures exceed 100 K. It is reported [1] that there exist two phases, low-Tc phase (2212) and high-Tc phase (2223). Synthesis of (2223) phase is the more difficult. It has been established [2] that addition of lead helps in the formation of highTc superconducting phase but the exact mechanism of the process is not clear. According to some authors [3], a melt is made by means of lead which is favourable for the growth of (2223) phase prior to (2212). On the other hand there are a number of authors who have pointed out that the lead content is greatly reduced with an increase in the time of synthesis [4, 5]. Many studies have shown that the concentration of lead in superconducting systems drops to zero [6]. This indicates the necessity of additional research aimed at specifying the actual role of lead in the formation of (2223) phase. Takano et al. [4] synthesized a B i P b S r C a C u O superconductor containing lead atoms for which they found Tc (0) at 107 K and a relatively large fraction of high-Tc phase. Thus, in crystal growth of the B i P b S r C a C u O system, it is necessary to develop a method to control the composition of the grown crystals precisely. Therefore, the flux method has been accepted as an important synthetic technique for growing single crystals in the oxide superconductors. The method allows the growth of crystals with a wide range of composition. The reason for this development is the need for large and perfect crystals for the application and study of their physical properties. Single crystal growth using various compounds as fluxes have been reported but many problems remain unsolved, such as the extraction of crystals from the flux material, the relatively small size of the crystals, uncontrolled cooling rates, the choice of a suitable flux, etc. Solute preparation is particularly important. Polycrystalline samples were prepared from Bi203, PbO, SrCO3, CaCO3 and CuO powders. The purity of all the starting materials was 99.9%. The powders were mixed to give a nominal starting composition of (Bil.4Pb0.6Sr2Ca2Cu3Oy). The mixtures were calcined at 800 + 5 °C and sintered at 845 + 5 °C in the repeating step of 24 h. Resistivity measurements show that Tc (0) was 106 + 1 K. This information confirmed the formation of high-Tc.

Preparation and characterization of Bi-based single crystals of high-T c superconductors

Preparation and characterization of Bi-based single crystals of high-T c superconductors

Growth of 80-K-phase Bi [sbnd]Sr [sbnd]Ca [sbnd]Cu [sbnd]O bulk single crystals using the flux containing Li or Sb

We prepared the Bi Sr Ca Cu O (Bi-based) bulk single crystals by a flux method using a starting material of Bi:Sr:Ca:Cu:Li = 2:1:1:2 - x:x(Li: x =0.2–1.4) or Bi:Sb:Sr:Ca:Cu = 2- y:y :1:1:2 (Sb: y =0.05–0.7). The plate-like Bi-based single crystals with a size of 3×4 mm 2 were obtained by using a starting material of x = 1.2. The X-ray diffraction patterns and the resistance-temperature characteristics indicated that the single crystal had an 80 K phase and its zero-resistance temperature was 85 K.