Microstructures of the melt-powder-melt-growth processed YBaCuO

Abstract

Microstructures of two MPMG processed YBaCuO materials with and without Y2BaCuO5 (211) inclusions were investigated by transmission electron microscopy. Using the MPMG process, it is possible to change the quantity of the 211 inclusions in the YBa2Cu3O7 (123) matrix. We prepared two YBaCuO samples with 0 and 30 vol. % 211 and with respective critical current density values of 2000 and 30 000 A/cm2 at 77 K and 1 T (magnetic field parallel to the c-axis). As possible pinning centers, we found stacking faults in the 123 matrix. However, we observed no appreciable change in their number and structure by introducing the 211 inclusions. Therefore, the difference in Jc values can be attributed to the 211 inclusion itself.

Effect of extremely fine Y2BaCuO5 precipitates on the critical current density of melt-processed YBa2Cu3Ox

“…Based on their transmission electron studies ͑TEM͒ they speculated that the clean and sharp Y 2 BaCuO 5 -YBa 2 Cu 3 O x interphase to be responsible for flux pinning. 41 However, this claim was not supported by other groups. [50][51][52][53] Based on the magnetization measurements, McGinn et al 50,51 reported a degradation of the critical current density with an increasing amount of Y 2 BaCuO 5 phase in zone-melted YBa 2 Cu 3 O x wires.…”

“…[23][24][25] In a high-T c superconductor various types of defects have been identified and claimed to be fluxpinning centers. [12][13][14] The defects observed in meltprocessed YBa 2 Cu 3 O x are twins, dislocations, 37,[43][44][45][46][47][48] stacking faults, [43][44][45] oxygen vacancies, Y 2 BaCuO 5 precipitates, [12][13][14][20][21][22][23][38][39][40][41][42][43][44][45] various other secondary phases, [46][47][48][49] etc. In particular, flux pinning by Y 2 BaCuO 5 precipitates has generated great interest in the superconducting community.…”

“…The QMG or MPMG technique used by Murakami et al resulted in a microstructure of homogeneously dispersed submicron sized Y 2 BaCuO 5 precipitates in a matrix of YBa 2 Cu 3 O x . [9][10][11][12][13][14]41 Whereas, the zone melting as used by McGinn et al 47,48 or the melt texturing as used by Jin et al 52,53 resulted in a microstructure of YBa 2 Cu 3 O x with large Y 2 BaCuO 5 precipitates ͑ϳ10 m͒. The fine precipitates found in QMG or MPMG samples were found to be beneficial for the enhancement of critical current density whereas the large precipitates were found to be ineffective.…”

“…The sharp Y 2 BaCuO 5 -YBa 2 Cu 3 O x interphase [12][13][14]41 as well as the defects associated with the Y 2 BaCuO 5 precipitates [42][43][44][45] has been proposed as a flux pinning centers. The difficulties encountered in the flux-pinning studies have resulted from a limited theoretical understanding of flux pinning and a diverse spectrum of crystal defects by which the flux lines may be pinned.…”

A generic process to introduce nanoparticles into powder preforms and its application to Infiltration Growth processing of REBa2Cu3O7 superconductor

“…On the other hand, uniform distribution of non-superconducting and inert inclusions such as of Y 2 BaCuO 5 (Y-211) is known to lead to effective flux pinning, without affecting the transition temperature. Enhanced surface area of fine-sized Y-211 inclusions, arising from large curvatures at their interface with the 123 matrix, gives rise to increased interfacial defect densities due to lattice mismatch [17]. Dopants like Y 2 O 3 [18], CeO 2 [19], ZrO 2 [13], BaCeO 3 [14], Al 2 O 3 [20], NiO [21], etc.…”