Phase relation in Y211–Y123–Ag system and morphology of silver in Y123 crystal

Abstract

Phase relation in the Y 2BaCuO 5 (Y211)– YBa 2Cu 3O 7− x (Y123)–Ag system, which is important for the fabrication of Y123/silver composite, and the morphology of silver particles dispersed in the Y123 matrix were investigated. The formation temperature of Y123 monotonously decreased to about 970°C as increasing Ag content up to a pseudo-monotectic composition and kept constant at the temperature with further Ag addition. The Y123/silver composite could be obtained at the temperatures lower than 970°C. These results suggest that Y123 phase is solidified by monotecto-peritectic reaction; Y211+L1 (Ba–Cu rich liquid)=Y123+L2 (Ag rich liquid). The morphology of silver particles in Y123 was altered by the addition of excess Y211. In the samples without excess Y211, silver particles dispersed in Y123 were disk-like shaped. On the other hand, those became spherical in the samples with excess Y211. The capturing mechanism of L2 liquid is considered to be the Uhlmann, Chalmers, and Jackson (UCJ) type pushing one. The amount of residual Y211 particles at the growth interface is considered to cause the morphological difference of captured silver between samples with and without excess Y211.