Phase formation and microstructure in Re1-x CaxBa2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics

Abstract

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.

X-ray crystal structures of Al-doped (Y,Ca)Ba2Cu3O7−ywhiskers

“…Actually, the influence of Ca doping in Y-123 has been widely studied from the point of view of its crystal structure both for polycrystalline material and for single crystals not grown with the whisker technique (Bö ttger et al, 1997;Chen et al, 2000;Stoyanova-Ivanova et al, 2006;Hijar et al, 1995). In principle, Ca should preferably substitute Y since the ionic radius of Ca 2+ (r = 1.12 Å ) is much closer to that of Y 3+ (r = 1.019 Å ) than to that of Ba 2+ (r = 1.42 Å ), and indeed X-ray structure refinements of single crystals have shown that at low Ca concentrations (< 11%) Y 3+ ions are substituted, while at higher concentrations Ca 2+ also replaces Ba 2+ (Bö ttger et al, 1997).…”