Ag distribution and columnar growth condition in unidirectionally solidified YBCO/Ag composites

Both suprerconducting and mechanical properties of Y-Ba-Cu-O superconducting oxide (YBCO) can be improved by fine Ag particles dispersed in Y123 (YBa2Cu3O7-x) matrix. The growth process of YBCO/Ag composite was investigated to clarify the solidification condition for producing columnar 123 crystals with Ag particles. Plate-like YBCO/Ag composites were horizontally solidified using Y123 + 15 mass%Ag particles and Y123 + Y2BaCuO5 (Y211) + 15 mass%Ag particles as starting materials. The distribution of Ag particles and gas holes were quantitatively measured and the changes in thermal conductivity and the effective temperature gradient were estimated by applying the rule of mixtures. Columnar 123 crystals developed under the critical solidification condition of G > 6 x 10(9).R for YBCO/Ag composites, while G > 4 x 10(9).R for Ag-free YBCO, where G was temperature gradient (K/m), and R was solidification rate (m/s).