High temperature phase relationships in (Y,Nd)-123 superconducting oxides:: the Y2BaCuO5-Nd4Ba2Cu2O10-Ba3Cu5Ox system

The quasi-ternary phase diagram of the Y2BaCuO5 (Y-211), Nd4Ba2Cu2O10 (Nd-422) and Ba3Cu5Ox ('035') system has been constructed in the vicinity of the peritectic temperature of YBa2Cu3O6-delta (Y-123) under air. The extent of the YxNd1-x+yBa2-yCu3O6+delta [(Y,Nd)-123ss] and liquid two-phase field is found to reduce with increasing temperature and tend towards the Nd-enriched region of the phase diagram via the emergence of a three-phase field of the '(Y,Nd)-123ss + (Y,Nd)-211 ss + liquid', followed by a '(Y,Nd)-211 ss + liquid' two-phase field. Furthermore, it is found that RE/Ba substitution in (Y,Nd)-123ss solid solution is significantly suppressed under reduced pO(2), limiting the stable field of formation of (Y,Nd)-123ss within the Y-123 and Nd-123 binary section of the phase diagram. This is in contrast with the wide composition and temperature stable region observed in the 'Y-123 + Nd-123 + Nd-213' quasi-ternary system under air.