A p p lie d Sup m o m hc titify Vol. 3. No. 4, pp. 229-235, 1995 zyxwvutsr Pergamon 0964~1807(95)00058-5 Copyright Q 1995 Elsevier Science Ltd Printed in Great Britain. All rights mewed 0964-1807/95 s9.50 + 0.00 zyxwvuts EFFECT OF EUTECTIC ADDITIONS AND SINTERING TEMPERATURE ON THE MICROSTRUCTURE, DENSITY AND CRITICAL CURRENT OF OXALATE DERIVED YBCO G. S. GRADER, G. E. SHTER, H. SHUFMAN and A. R. SCHWARTZMAN Chemical Engineering Department, Crown Center for Superconductivity, Technion, Haifa 32000, Israel (Received 4 October 1994; in revised form 3 March 1995) Abstract--The effects of eutectic (BaCuOl+CuO) additions and sintering temperahue on the morphologr, density and critical current of extruded YBCO wires, were investigated systematically over a wide range of temperatures (800-975°C) and compositions (040 mol%). The YBCO-eutectic system was classified morphologically into five distinct regions, which are influenced strongly by the sintering temperature. The main effect of the eutectic dopant is prevention of the sharp drop of critical current, observed in pure YBCO, at sintering temperatures above 920°C. This effect is facilitated by suppression of exaggerated anisotropic grain growth and the development of visible intergranular cracks in material. INTRODUCTION The progress in application of HTSC materials depends on the advances in melt processing technology (MPT) [l-4]. However, issues regarding reactive power synthesis and normal sintering procedures have not been fully explored. In this context conventional sintering is on the one hand an important preliminary step in MPT processes, and on the other hand a significant and independent technology for production of non-textured bulk material. Some of the basic problems of sintering are carrying out the process at relatively low temperatures, prevention of the HTSC decomposition, maintaining the required shape of the samples, and at the same time providing the required density, mechanical and chemical stability of the material. In the YBCO superconductor, dopants such as Ag, Ag20, PtO,, Ce02, Sn02, Zr02, BaTi03, Sic, BaSnO3, BaZQ, SrTiO3 [5-161, have been used to influence the material properties. Compounds from the Y-Ba-Cu-0 system (e.g. CuO, BaCuOl and Y2BaCu05) have also been incorporated [5,, 17-231. In the latter case these compounds may be present non-intentionally as by-products of YBCO synthesis, resulting from nonstoichiometry and/or incomplete conversion of starting materials and intermediate phases. Since the presence of the above by-products is very common, it is important to elucidate the influence of their concentrations on the properties of sintered materials. Additions of CuO and BaCu02 in the Y-Ba-Cu-0 system lead to binary and ternary low melting (890-92O’C) eutectic mixtures, producing liquids that enhance the densification of the material [24]. The effect of doping YBCO with single components such as CuO, BaCuO2 has been studied [ 17-231. Other investigations were directed at phase diagram evaluation [24]. In all cases the range of the work was limited from the stand point of simultaneous temperatures and composition variations. Additionally, the previous work was based on solid state derived powders, calcined at high temperatures, which naturally narrowed the temperature range of the investigations. Extension of this range is possible by using highly reactive powders derived by methods such as sol-gel and coprecipitation [25, 261. The effect of CuO and BaCu02 additions in the binary eutectic ratio, in wide compositional and temperature ranges have not been performed. Therefore the general purpose of this work is to investigate systematically the joint effect of eutectic additions and sintering temperature on the morphology, densification and superconducting properties of bulk YBCO derived by oxalate coprecipitated powders [26]. 229