BOLETÍN DE LA SOCIEDAD ESPAÑOLA DE Cerámica y Vidrio A R T I C U L O • • • Textured superconductors: progress ¡n processing and development of applications X.OBRADORS, B.MARTÍNEZ, F.SANDIUMENGE, S.PIÑOL, J.FONTCUBERTA, V.GOMIS, X.GRANADOS, A. GOU, R.YU, N.VÍLALTA AND J.MORA Institut de Ciencia de Materials de Barcelona , C.S.I.C. Campus Universität Autónoma de Barcelona. 08193 Bellaterra, Catalunya, Spain The present review stresses the potentiaHty of directional soHdification techniques for the preparation of bulk YBa2Cu307/Y2BaCu05 composites with high critical currents useful for several applications . We analyse the growth mechanisms and we show how the size of 211 precipitates can be refined . We also present detailed TEM investigations of the defect formation mechanisms and a complete investigation of the influence of 211 phase concentration on the critical currents . The pinning mecha- nisms have been identified from the field (up to 20 T) and temperature dependence of the critical currents . This allow us to propo- se the first complete magnetic phase diagram of these type II superconducting materials . Finally , we stress the potential of these melt textured ceramics in several technological applications such as current leads, fault current limiters, flywheel batteries and hys- teresis motors. key words: Ceramic superconductors, directional solidification, microstructure, critical currents, flux pinning centres, applications of YBa2Cu^Oy. Superconductores texturados: avances de procesamiento y desarrollo de aplicación La presente revisón enfatiza la capacidad de las técnicas de solidificación direccional para la preparación de materiales compuestos masivos de YBa2Cu307/Y2BaCu05 (123/211) con elevada corriente crítica útiles para varias aplicaciones. Analizamos los meca- nismos de crecimiento y mostramos como se puede reducir el tamaño de las inclusiones de 211. También presentamos una investi- gación detallada de los mecanismos de formación de defectos mediante microscopía electrónica de transmisión (TEM), así como de la influencia de las inclusiones de 211 sobre la corriente crítica. Los mecanismos de anclaje de flujo se han identificado a partir de las dependencias de la corriente crítica con el campo magnético (hasta 20 T) y la temperatura. Ello nos permite proponer el primer dia- grama de fases magnético de estos materiales superconductores de tipo II. Finalmente, enfatizamos la potencialidad de estas cerá- micas texturadas mediante fusión en varias aplicaciones tales como barras de alimentación, limitadores de corriente, sistemas de almacenamiento de energía inerciales y motores de histéresis. Palabras clave: Superconductores cerámicos, solidificación direccional, microestructura, corrientes críticas, anclaje de flujo magnético, aplicacio- nes del YBa2CußOy. 1. INTRODUCTION Directional solidification is one of the most promising pro- cessing methodology which allows to prepare bulk supercon- ducting YBaCuO ceramics having high critical currents. Among all the different versions of melt processing of YBCO now being investigated (see ref. 1 - 4 for recent reviews) the use of external parameters such as temperature gradients (5), mag- netic fields or seeds (6), generate a driving force for the growth of YBCO with well defined crystallographic orientations. Grain boundaries are not, however, the unique crystallo- graphic defect having some influence on the superconducting performance of bulk YBCO monoliths. There are many defects which have been identified in 123/211 ceramic composites and their concentration and mutual interaction strongly depends on the processing methodology. It seems clear then that a full investigation of the defect formation mechanisms in relations- hip with the procesing methodology and with the critical currents of these materials needs to be carried out. It's also straighforward to note that the relevance of the defects as pinning centers will strongly depend on their con- centration, magnetic field orientation and the position chosen in the H-T magnetic phase diagram, where vortex interaction and fluctuation effects may strongly differ. It's then very important to relate any given defect in melt textured 123/211 composites to their general behavior under different physical situations. In this paper we review some recent progress in the unders- tanding and improvement of directional soHdification proces- sing techniques which allow to prepare long single domain textured ceramics and we describe new evidences for the sub- tle relationship between microstructure and pinning mecha- nisms in these materials. Finally, we briefly describe some applications which can be Bol. Soc. Esp. Cerám. Vidrio, 36 [2-3] 123-131 (1997) 123