Tailoring Microstructures Under Strong Non-Equilibrium Conditions: A Feasible Path Towards High J C in Melt Textured YBa
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TAILORING MICROSTRUCTURES UNDER STRONG NON-EQUILIBRIUM CONDITIONS: A FEASIBLE PATH TOWARDS HIGH JC IN MELT TEXTURED YBa2Cu3O7 Felip Sandiumenge1, Jérôme Plain1,2, Teresa Puig1, Xavier Obradors1, Jacques Rabier2 , Maria J. Martínez3 1 ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra, Spain 2 LMP, Université de Poitiers, SP2MI, 86960 Futuroscope-Chasseneuil, France 3 ICMM-CSIC, Cantoblanco, 28049 Madrid, Spain ABSTRACT Melt textured YBa2Cu3O/Y2BaCuO5 were post processed by high oxygen pressure for different periods and temperatures. This process permits the control of the microstructure, in particular the growth and shape of the stacking faults and thereby the partial dislocation density. Analysis of the Jc(H,T) behavior allow to separate the contribution of Y2BaCuO5 interface from that of dislocations. It is shown that the in-plane partial dislocations act as point-like pinning centers increasing Jc up to 180% but this enhancement factor is counterbalanced by the effect of the stacking faults associated to the partial dislocations. INTRODUCTION Tailoring the microstructure in melt textured YBa2Cu3O7 (123) superconductors is a complex issue which allows to increase the critical currents. It has been shown by several authors that non-superconducting inclusions such as Y2BaCuO5 (211) enhance flux pinning in these materials [1,2] but some controversy has been raised concerning the microscopic mechanisms, i.e. some authors have suggested that the defects associated to the interface bear the responsibility to enhance the flux pinning [3]. In recent works we have shown that high oxygen pressure (HOP) post-processing treatments allow to increase the critical current density up to 180 % and that this pinning enhancement can be associated with the formation of partial dislocations bounding stacking faults[4,5]. In the present work we investigate further this non-equilibrium transformation of the microstructure of melt textured grown (MTG) 123/211 composites and separate the contribution to flux pinning of the dislocations from that of 123/211 interface. It is clearly settled then that interface pinning and the defects associated to the interface have a distinguishable contribution to the critical currents. EXPERIMENTAL Highly textured 123/211 composite having a final 211 content of 30%wt was obtained by top seeding growth [6] followed by an oxygenation process at T=450ºC , PO2 = 1 bar during 120 h. The single domain was cut in samples 3×3×3mm3 in size. Afterwards the samples were post processed under different conditions: all the processes were performed at PO2=100bar, the first set at constant time (t=12h) at different temperatures: T=350ºC, 450ºC and 600ºC, and the second set at constant temperature (T=600ºC) for different periods of time: t=1h, 2h and 12h. Magnetization measurements were performed by SQUID magnetometry with the field applied parallel to the c-axis. Critical current densities were calculated using the generalized Bean II7.6.1
model. Transmission Electron Microscopy (TEM) foils were polished down to perforati
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