Grain boundaries in high temperature superconducting ceramics

Abstract

International audienceThe aim of this paper is to review the different types of grain boundaries found in YBa₂Cu₃O_7-d superconducting ceramics which have been investigated over the past decade. A variety of samples covering a wide range of current density Jc values are examined including: classical bulk ceramics, melt-textured bulk ceramics, bulk and thin film bicrystals with specific orientations, thin films and single crystals. From electronic coupling, Jc is expected and found to decrease with increasing grain boundary (GB) misorientation. From the magnetic behaviour, the critical current density Jc(H) is expected to increase with the number of pinning centres. The properties of the various types of GB's are discussed. All the studies reviewed lead to the conclusion that grain boundaries in YBCO materials cannot be understood without specific information about their local composition, structure and electronic state. They confirm that research on bicrystals is crucial for high-temperature superconductor development

Bulk nanocrystalline superconducting YBa2Cu3O7-x

“…This is attributed to weak transmission across d-wave grain boundaries at large misorientation angles [1][2][3][4][5]. Several techniques have been investigated to increase J C , including increasing the flux pinning through nano-particle additions [6] and improving the superconducting properties of the grain boundary [7][8][9].…”

Current Flow and Flux Pinning Properties of YBCO Foam Struts

“…(ii) The struts show the presence of an internal granularity due to embedded grains (YBCO and 211) in the main YBCO matrix and subgrains, which also force the currents within a single strut to flow across grain boundaries (GBs). As the GBs of YBCO are obstacles to the current flow [27], [28] and the struts only have a limited extension, this reduces j c considerably. Table I lists the current densities of all foam struts obtained at an applied field of 1 T, which is already very large for currents across GBs.…”

Nanocomposite structure and reactivity of perovskites based on lanthanum manganites

“…For the oxidation reactions efficiently catalyzed by mate rials containing transition metal cations (manganites, cobaltites, ferrites), no universal dependence of the activity on the electron state of the transition metal cations, defect concentration, and surface and bulk oxygen state has been revealed . This could be due to the nonmonotonic change of the physicochem ical characteristics caused by specificity of the real/defect structure and microheterogeneity of per ovskites, depending on their composition, the method of preparation, the temperature, and the partial pres sure of oxygen [2,3,7,. However, these fea tures are as a rule not taken into account in describing the catalytic properties of mixed oxides.…”

“…Mixed oxides with perovskite like structure are widely used in present day technologies as magnetic, ion conducting, catalytic, and construction materials [1][2][3][4][5][6][7]. For these materials, a strong interrelation between their structural, transport and magnetic char acteristics is observed.…”