DOI: 10.1007/s11532-005-0013-x Research article CEJC 4(1) 2006 166–173 Phase formation and microstructure in Re 1-x Ca x Ba 2 Cu 3 O z (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics A.K. Stoyanova-Ivanova 1∗ , S.D. Terzieva 1 , A.D. Staneva 2 , V. Mikli 3 , R. Traksmaa 3 , Y.B. Dimitriev 2 , V.T. Kovachev 1 , 1 Institute of Solid State Physics, Bulgarian Academy of Science, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria, 2 Department of Silicate Technology, University of Chemical Technology and Metallurgy, 8 Kl. Ohridski, 1756 Sofia, Bulgaria 3 Centre for Materials Research, Tallin Technical University, Ehitajate 5, Tallin 19086, Estonia Received 1 September 2005; accepted 30 October 2005 Abstract: We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE 1-x Ca x Ba 2 Cu 3 O 7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. c Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved. Keywords: REBCO superconducting ceramics, Ca-substitution, microstructure, morphology 1 Introduction Recently one of the most extensively studied substitution in REBa 2 Cu 3 O 7-δ systems is divalent Ca 2+ for trivalent RE 3+ (RE=Y, Eu, Er) [1–3]. According to Hatada, et al.[1], * E-mail: angelina@issp.bas.bg; mira@issp.bas.bg