ON THE CHARACTERISTICS OF PERITECTIC GD2BACUO5 AT THE PRO-PERITECTIC STAGE WITH INCREASING AMOUNTS OF EXTERNAL GD2BACUO5

The effect of different amounts of Gd2BaCuO5 (211) in the starting com position of GdBa2Cu3O7-y (123) on the formation and refining behaviour of the 211 phase particles produced during the peritectic decompositi on of 123 has been investigated. In the absence of any extra 211 in th e liquid in the pro-peritectic stage, the morphology of the peritectic ally formed 211 particles is acicular with high aspect ratios; whereas , even small amounts of already existing 211, by acting as nucleating sites for the 211 generated by the decomposition of 173, change the mo rphology from acicular to circular. The average size of the 211 is fou nd to decrease according to an inverse power law with respect to the n umber of nucleating centres. The change in morphology is discussed and a quantitative analysis of the average sizes of the 211 is presented. (C) 1998 Elsevier Science B.V.