From imperfect to perfect Bi₂Sr₂CaCu₂O_x (Bi–2212) grains

Abstract

The 2212 phase formation during annealing of melt textured Bi–2212 (Bi2Sr2CaCu2Ox) was investigated using differential thermal analysis, thermal gravimetric analysis, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and high resolution transmission electron microscopy. After zone melting, the material is multiphase consisting of 2212, 2201, Sr1−xCaxCuO2, and the eutectic. The 2212 phase formed is highly perfect with less than 5% intergrowths of 2201 layers; the 2201 phase shows no intergrowth of 2212 at all. In the first period of the annealing, remelting of the eutectic leads to fast oxygen diffusion and a high 2212 formation rate. The 2201 → 2212 transformation proceeds via intermediate states of high defect density. The 2212 grains contain up to 30–70% 2201 intergrowths. Further heat treatments lead to an annihilation of the great majority of intergrown 2201 layers. We propose a model for the formation of 2212 grains with a low planar defect density, based on frequent stacking faults, that allows diffusion of Ca- and Cu-atoms over a short distance. The model provides a schematic description of this solid-state process and correlates it to the characteristic microstructural features of melt-processed Bi–2212.

Application of elevated magnetic fields during growth of BiSrCaCuO superconducting whiskers and studies of growth defects for better understanding of the growth mechanism

“…For the BiSrCaCuO un-doped ceramic, 'nucleation and growth' type mechanisms or mechanisms involving a liquid phase are described in the Ref. [45][46][47][48][49][50][51][52][53][54], but several other growth models, such as intercalation, exchange, pipediffusion, one-dimensional diffusion along the caxis, epitaxial growth starting from a primary phase [45][46][47][48][55][56][57][58][59][60][61][62][63][64] were also introduced. Generally, these models are considered to belong to the so-called 'solid-state' growth models, although a clear separation between them or between them and 'nucleation and growth' models is difficult and many articles reported simultaneous occurrence of several mechanisms.…”

Review on Bi–Sr–Ca–Cu–O whiskers

“…(1) In the case of whiskers the proposed mechanism is mainly a solid-liquid one and it corresponds to the 'nucleation and growth', 'dissolution and crystallization' or other mechanisms involving liquid phases [74][75][76][77][78][79][80][81][82][83] for the Bibased superconducting phases in the BSCCO system without impurities. At the same time for the BSCCO system without impurities solid-solid type growth mechanisms such as intercalation, exchange, pipe-diffusion, and onedimensional diffusion along the c-axis [74][75][76][77][84][85][86][87][88][89] or 'epitaxial' growth mechanisms [90][91][92][93][94][95] were introduced. Considering that, in the whiskers, intergrowth of Bi-2223 into Bi-2212 structure is frequently detected (especially by transport measurements), it is possible that, to some extent, solid-solid and epitaxial mechanisms are active during whisker growth.…”

Processing of electroplated Bi-2212/Ag tapes using a melt-quench and annealing method

“…After the consumption of the liquid phase, the reaction mechanism changes to a solid-state reaction, Bi-2201 + (Sr, Ca)CuO2 → Bi-2212, which is a much slower process. As observed from transmission electron microscopy (TEM) measurements [8], although there were no Bi-2201 grains observed in samples that were melt-quenched and annealed for a shorter time, there were many 2201 intergrowths inside the Bi-2212 grains.…”