Texture of Y‐ and Bi‐HTSC and Methods for its Determination

Abstract

Investigation of the texture of Y-and Bi-HTSC materials by X-ray techniques involves certain difficulties owing to the peculiarities of their crystal structure which causes the arrangement of reflexes in dense groups and practically precludes the formation of a pole figure from an isolated reflex. The texture of Y-and Bi-HTSC materials has been investigated by constructing direct pole figures tn an automatic texture diffractometer DAPT YM1 in CuKa emission from groups of reflexes which are unresolvable under the test conditions. The choice of groups of reflexes was dictated by the type of texture formed. With a basal texture of packing of powders, the following groups have turned out to be the most suitable for the YBa2Cu307-x phase (123): (013) + (110) + (103), 20 = 32.3-32.8" and (014) + (005) + (104), 28 = 38.5-38.8'. They include the reflexes which are structural and superstructural relative to a bcc subcell with a rather slight orthorhombic distortion, with its tripling along the "c" axis forming a cell of (123) Single crystals and polycrystalline materials based on HTSC relate to a group of hard substances with a high liability to brittle fracture (GRABKO et al., GROZAV et al.; DEMIRSKY et al.; Nr et al.): HTSC powders, owing to pronounced anisotropy of their properties (LABORDE et al.; SHAMRAY; WATANABE et al.), acquire a non-equiaxed shape of particles on fracture of crystals, with a particular preferable orientation of fracture planes. In the course of deformation (uniaxial compression, rolling), Y-and Bi-HTSC-based materials, as a rule, acquire a basal (001) texture (LUSNIKOV et al.; SHAMRAY et al.; STARCHENKO et al.; WENK et al.), which has a noticeable effect on their mechanical and superconductive properties (HUANG et al.; LABORDE et al.; WATANABE et al.). Basides, the appearance of the basal texture should be taken into consideration when determining the crystal structure parameters and phase composition of polycrystalline specimens by methods of neutronographic and X-ray structural analysis. In the present work, the method of X-ray structural analysis has been developed and the texture of cold-rolled and annealed thin strips based on the phases YBa2Cu30, --x (123) and Bi2Sr,CaCu,0B (2212) has been determined. Materials and methodsThin strips of Y-and Bi-HTSC materials were prepared by cold rolling of practically single-phase powders of these materials (295% by vol. of the main phase) with 2-10% of a viscous binder. The

Critical Currents in a Composite Superconductor

“…Since the c-axis texture is the type of texture that is interesting in texture studies in high T c ceramic materials the 2 θ value of the (0010) plane was mainly used because it gives the maximum intensity. A list of some main (hkl) and the corresponding 20 and χ values are given in Table 3.4 (Shamray et al 1991). The samples were polished very carefully to give a surface as smooth as possible.…”