The isothermal melt-texturing of bulk YBa₂Cu₃O_7-xceramics: from cooking to modelling

Abstract

Various techniques for the synthesis of bulk YBa2Cu3O7-x ceramics are reviewed. The microstructure of melt-textured YBa2Cu3O7-x compounds is described. In contrast to the relatively simple processing of such materials, the complexity of the microstructure at a mesoscopic scale is underlined. A model describing the various features of the microstructure of YBa2Cu3O7-x compounds is described. The obtained results are discussed for various initial conditions and are favourably comparable with experimental findings.

Foam-like evolution in polycrystalline systems following successive ‘melt and growth’ cycles

“…A better fit can be obtained for , / ( A / ( A ) ) using an 'extended Louat law' such as where X is a free parameter characterizing some scale invariance of the cellular structure. This law was discussed in recent works about random agglomeration (Bosco 1995) and about image analysis of composites (Vandewalle 1998). A value X M 0.9 was obtained for the present data.…”

“…The present model is however based on the Eden model (Eden 1961, Jullien andBotet 1985). The relevance of the Eden model in the crystal growth field, especially in the case of ceramics, has been discussed elsewhere (Vandewalle et al 1997, Vandewalle 1998. In short, the Eden model is relevant (i) if one considers the sites of the lattice as mesoscopic units, and (ii) if the growth is isothermally controlled.…”

From RE-211 to RE-123. How to control the final microstructure of superconducting single-domains

“…The microstructure of single-domain (RE)BCO superconductors is highly dependent on the processing conditions and the presence or not of additives [19,27,[30][31][32][33][34][35][36]. A variety of meltprocessing techniques has been developed to produce singledomain (RE)BCO superconductors [11,18,[37][38][39][40][41][42][43][44][45]. All these techniques are based on the peritectic reaction 2(RE)Ba 2 Cu 3 O 7−δ(s) → (RE) 2 BaCuO 5(s) + Ba 3 Cu 5 O 8(l) + yO 2(g) .…”

“…Nevertheless, large singlegrains can be produced by peritectic recombination from the RE-211 + liquid state. In this case, quasi-crystals with a lot of defects can be obtained [11,[17][18][19]. Defects such as the presence of the RE 2 BaCuO 5 (RE-211) secondary phase in the RE-123 matrix, which results from the incomplete peritectic recombination, can act as pinning centres for vortices in the superconducting state and thus help to increase J c [20][21][22][23][24].…”

Effects of Nd123/MgO Thin Film and MgO Single-crystal Seeds in Isothermal Solidification of YBaCuO/Ag

“…The nominal composition corresponds to the final phase composites of Y123 + 0.4 Y211, which is widely believed to be an optimum ratio for refining of Y211 precipitates, hindering of liquidphase loss, improvement of stable morphologies, and enhancement of flux pinning. 1,17,18 After calcination in air at 900°C for 30 h with an intermediate grinding, the powders of 10 wt% Ag 2 O and 0.5 wt% Pt were added. The resultant powder was uniaxially pressed into a pellet 20 mm in diameter and 7 mm in thickness.…”