Grain alignment in bulk YBa₂Cu₃O_x superconductor by a low temperature phase transformation method

A quench and directional phase transformation process has been developed to achieve grain alignment in bulk YBa₂Cu₃O_x superconductors at temperatures about 100°C below the peritectic temperature. Isothermal phase transformation of quenched precursors at 890°C for 3 min is found to result in the formation of more than 75% of YBa ₂Cu₃O_x phase without any formation of Y ₂BaCuO₅. Phase transformation at higher temperatures leads to rapid formation of Y₂BaCuO₅ in addition to YBa ₂Cu₃O_x. A well-aligned microstructure is achieved by directional phase transformation of the quenched compacts as a rate of 10 mm/h. The magnetic field dependence of the critical current density at 77 K of the directionally phase transformed material compares well with that of melt-textured YBCO and is superior to that of magnetically aligned and sintered YBCO.