The effect of the addition of zirconium-containing compounds on the microstructure and superconducting properties of mono-domain Y-Ba-Cu-O bulk superconductors

摘要

The effect of the addition of BaZrO_3 and YBa_2ZrO_(5.5) zirconium-containing compounds on the microstructure and superconducting properties of single-domain Y-Ba-Cu-0 (YBCO) bulk superconductors has been investigated for various levels of Zr content. The distribution of Y_2BaCuO_5 (Y-211) particles along both the crystallographic a and c axes of the YBa_2Cu_3O_y (Y-123) superconducting matrix is observed to be rather discontinuous in Zr-containing samples, even with a small amount of secondary phase addition. The YBCO microstructure is observed to separate into regions of high and low concentrations of Y-211 particles when Zr-containing compounds are added to the precursor powder. Furthermore, Y-211 particles are observed to accumulate along the growth sector boundaries in the Y-211 free region of the Y-123 matrix. The extent of the Y-211 free region increases with increasing zirconium content. Increased concentrations of zirconium-containing compounds in the precursor powder trigger an undesirable segregation within the melt-processed microstructure of a band consisting of a liquid channel and a high concentration of Y-211 particles in both a and c axis growth sectors. The addition of BaZrO_3 and YBa_2ZrO_(5.5) to the precursor powders does not affect the superconducting transition temperature, T_c, of the bulk material. Critical current densities, J_c, of around 60 000 and 47 000 A cm~(-2) in self-field at 77.3 K were recorded for the samples containing 0.329 mol percent BaZrO_3 and 0.658 mol percent YBa_2ZrO_(5.5), respectively.