Growth features and intergranular connectivity of melt processed YBCO

Bulk, high temperature superconductors have significant potential for use as powerful permanent magnets in a variety of practical applications due to their ability to trap record magnetic fields. In this paper, soft ferromagnetic sections are combined with a bulk, large grain Y-Ba-Cu-O (YBCO) high temperature superconductor to form superconductor/ferromagnet (SC/FM) hybrid structures. We study how the ferromagnetic sections influence the shape of the profile of the trapped magnetic induction at the surface of each structure and report the surface magnetic flux density measured by Hall probe mapping. These configurations have been modelled using a 2D axisymmetric finite element method based on the H-formulation and the results show excellent qualitative and quantitative agreement with the experimental measurements. The model has also been used to study the magnetic flux distribution and predict the behaviour for other constitutive laws and geometries. The results show that the ferromagnetic material acts as a magnetic shield, but the flux density and its gradient are enhanced on the face opposite to the ferromagnet. The thickness and saturation magnetization of the ferromagnetic material are important and a characteristic ferromagnet thickness d* is derived: below d*, saturation of the ferromagnet occurs, and above d*, a weak thicknessdependence is observed. The influence of the ferromagnet is observed even if its saturation magnetization is lower than the trapped flux density of the superconductor. Conversely, thin ferromagnetic discs can be driven to full saturation even though the outer magnetic field is much smaller than their saturation magnetization. [5,6]) is well beyond the saturation magnetization of conventional ferromagnets. This makes them extremely promising as a competing technology for traditional permanent magnets in various applications [7][8][9][10]. The combination of ferromagnetic and superconducting materials can enhance the performance of the superconductor [11,12] and even lead to new applications [13]. Large grain, bulk superconductors are often used in applications that incorporate ferromagnetic materials, such as in motors and generators [14,15]. Ferromagnets can also increase the force in levitation systems [16,17] and close the magnetic circuit, which improves the available flux produced by bulk superconductors [18]. Similarly, ferromagnetic materials are used as sheaths around multifilament wires and tapes [19,20] or as magnetic flux diverters to modify the flux distribution around tapes and superconducting coil magnets [21][22][23][24][25][26][27][28]; thereby improving their electrical properties (i.e. increasing the critical current and reducing AC losses).

Section: Measurement Resultsmentioning

confidence: 99%

Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor

Philippe

Ainslie

Wera

et al. 2015

“…The surface of the single domain is characterized by the presence of parallel lines perpendicular to the macroscopic growth direction of the domain. Under higher magnification it is observed that these lines are composed of Y-123 phase layers with parallel edges and therefore correspond to the aor b-axis facet lines derived from the tetragonal symmetry in the a-b plane of the single domain [18]. This is because the Y-123 phase has a tetragonal crystal structure at the grain growth temperature.…”

Section: Resultsmentioning

confidence: 90%

Observations of the influence of Y-211 inclusions on melt textured growth of single domain Y–Ba–Cu–O

Xu¹,

Wu²,

Qiu³

2007

Single domain Y–Ba–Cu–O (YBCO) samples composed of a YBa2Cu3O7−δ (Y-123) matrix with Y2BaCuO5 (Y-211) inclusions were fabricated using the top-seed melt-textured growth (TSMTG) process. The influence of the Y-211 inclusions on the melt-textured growth mode has been studied for precursor pellets with a Y-123:Y-211 molar ratio of 1:0.2, 1:0.3 and 1:0.4. The surface morphologies obtained from these sintering pellets quenched from 1000 °C, 997 °C and 994 °C, respectively, have revealed that the initial peritectic recombination process near the seed crystal seems to take place earlier for the Y-123 matrix with low Y-211 inclusions than for that with a high level of Y-211 inclusions; however, the melt-textured growth rate of the single domain seems to be faster in the system with a high level of Y-211 inclusion than in that with a low level.

“…The top surface is parallel to the (001) plane of the crystal lattice, and there are three major crystallographic directions in it: All possible shapes of initial facet plane generated by elongated seeds depending on the seed crystallographic orientation were analysed. As reported in [9], the seed generates an initial facet plane of rectangular shape whose edges are parallel to the directions a irrespective of the seed shape, as can be seen in figure 1. Taking this into account one can suppose that in the ideal case the elongated seed whose edges are parallel to the a directions generates the initial facet plane of rectangular shape corresponding to the form of the seed contact surface.…”

Section: Preparation Of Elongated Seedsmentioning

confidence: 84%

Employment of Gd–Ba–Cu–O elongated seeds in top-seeded melt-growth processing of Y–Ba–Cu–O superconductors

Nizhelskiy¹,

Poluschenko²,

Matveev³

2006

Top-seeded melt-growth (TSMG) processing of large bulk Y–Ba–Cu–O monodomains was advanced by applying Gd–Ba–Cu–O elongated seeds. The seeds, up to 38 mm in length, were fabricated by cutting Gd–Ba–Cu–O monodomains produced by the TSMG technique. Three types of seeds, differing in their orientation of crystallographic directions, were prepared. Crystal growth of the Y–Ba–Cu–O monodomain depending on crystallographic directions in the seed contact surface was investigated. It was established that every type of seed generates a different growth mode of the initial facet plane. It is shown that elongated seeds make for growth of a dominant crystal without spontaneous nucleation, decrease of processing time, reduction of maximum heating temperature and improvement of manufacturability and reproducibility of the TSMG process. Y–Ba–Cu–O monodomains up to 48 mm in diameter were produced using elongated seeds. They are able to trap magnetic fields up to 1.38 T.