Interrelation of preparation conditions, morphology, chemical reactivity and homogeneity of ceramic YBCO

Abstract

Abstract YBa2Cu3Oy ceramics having different morphologies: low porosity, composed of well shaped and closely connected large crystal grains, high porosity, composed of badly packed irregularly shaped small grains, and of intermediate microstructure,were investigated with respect to reactions that lead to the deviation of oxygen content from its equilibrium value and loss of homogeneity of oxygen ion distribution. These reactions, which occur during quenching performed after the equilibrium of YBCO with oxygen has been attained, are the oxygen absorption during quenching in liquid oxygen or in common liquid nitrogen (containing 2–3% dissolved oxygen) and the oxygen release during quenching in pure liquid argon. In these reactions and in the reaction with CO2 impurities during attaining equilibrium (which also leads to an inhomogeneous sample), the reactivity of the investigated ceramics varied from high (in high porosity ceramic) to almost inert (in low porosity ceramic), while even an almost inert ceramic attains equilibrium under 0.01–1 atm O2 and 450–920 °C during less than 35 h. Therefore this ceramic is most suitable for preparation of the samples having any oxygen content. The interrelations found make it easier to search for the proper conditions of ceramic sintering, equilibration with oxygen and quenching for preparation of both homogeneous and inhomogeneous samples having the desired morphology and properties.