Solidification of YBa2Cu3O6+δ: Part I. Morphology

Abstract

A new quenching technique was used for detailed microstructural examination of quenched YBa2Cu3O6+δ/liquid interfaces. The examination revealed that the growth rate and the amount of excess Y2BaCuO5 (211) had a strong influence on the growth morphology of YBa2Cu3O6+δ (123). The maximum growth rate at which single crystal growth could be obtained increased from 1 μm/s to 1.5 μm/s as excess 211 content increased from 0 to 20 wt. %. It then decreased to 1 μm/s as excess 211 increased to 40 wt. %. Dendritic growth with distinguishable secondary arms occurred for stoichiometric 123 samples in the regime of cellular/dendritic growth. A highly curved 123 envelope was formed on 211 particles located at the 123 growth interface for stoichiometric 123 samples in the regime of single crystal growth. The microscopic 123 growth interface became flat as excess 211 content increased to 20 wt. %. The engulfment of 211 particles into 123 matrix is discussed based on detailed microstructural examination. It is found that the formation of a small highly curved 123 envelope on 211 particles for stoichiometric 123 samples is due to the large 211 particle spacing.