Microstructural characterization of quenched melt-textured YBa₂Cu₃O_7−δ materials

Abstract

The microstructure of YBa2Cu3O7−δ (YBCO) materials, melt-textured in air and quenched from the temperature range 900–;990 °C, has been characterized using a combination of x-ray diffractometry, optical microscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry. BaCu2O2 and BaCuO2 were found to coexist in samples quenched from the temperature range 920–960 °C. The formation of BaCu2O2 preceded the formation of YBCO. Once the YBCO had formed, BaCu2O2 was present at the solidification front filling the space between nearly parallel platelets of YBCO. Large Y2BaCuO2 particles at the solidification front appeared divided into smaller ones as a result of their dissolution in the liquid that quenched as BaCu2O2.

Studies of the phase evolution of YBCO materials with different additives

“…Previous results on stoichiometric Y123 samples [3] showed that the melt quenched from 990 • C consisted solely of BC1 and CuO and that BC2 formed on samples quenched from 960 • C and lower temperatures (before Y123 formation). Therefore, there must be a region of stability of BC2 in air at some temperature below 990 • C. In the case of samples of Y123+20 mol% Y211 only a peak in the volume fraction of BC1 is observed at approximately 995 • C (see table 3).…”

“…Samples are produced using techniques described elsewhere [3,4]. Briefly, precursor powders of Y123 and Y211 are produced by co-precipitation and calcined separately.…”

“…One of the reasons for the lack of characterization of the quenched melt is its rapid degradation on exposure to atmospheric humidity [1,2]. However detailed quenched melt microstructures can be observed if sufficient precautions are taken to minimize the degradation [3,4].…”

Functional imaging and assessment of the glucose diffusion rate in epithelial tissues in optical coherence tomography

“…The microstructure of the type II regions also shows that they are formed from stoichiometric Y123 particles. The large, segregated regions of BC1 and BC2, characteristic of Type II regions, are also observed in stoichiometric Y123 samples that have been quenched above the Y123 solidification temperature [16]. The large, blocky Y211 particles observed in type II regions are also present in pure Y123 samples [17] and are very different to the morphology and size of the Y211 particles present in samples with CeO 2 or Y 2 O 3 additions [18].…”

Crystallization features of YBa2Cu3O7‐δ in the Y2BaCuO5‐BaCuO2‐CuO and Y2Cu2O5‐BaCuO2 systems

“…They are 31, 39 and 54 K/J·m for the systems (II), (I) and (III), respectively. [8,10]. However, during the investigation of the microstructure of the tempered samples, the formation of the YBa 2 Cu 3 O 7-δ compound was found to be not on the border between the grain surfaces and the solution-melt, but rather in the ellipsoid regions of the crystallized solution-melt ( fig.4).…”