Effect of Carbon on the Microstructure and Superconducting Properties of YBa₂Cu₃O₇₋ₓ Melt-Textured Crystals

YBa ₂ Cu ₃ O _7-x (123) high-temperature superconducting powders were synthesized by mixing cost effective Y ₂ O ₃ , CuO and BaCO ₃ precursor powders and subsequently reacting them at 920°C in a rotary calciner. The effects of carbon on the critical temperature (T _c ), critical current density (J _c ), trapped field as well as the growth of melt-textured 123 crystals were examined as a function of the extent of calcination. Increasing carbon content in the sample resulted in lower T _c and zero field J _c , however, high field J _c were improved showing a 'fishtail' effect at 77 K. In addition, the nucleation and growth process of 123 crystals was not affected by the carbon content, but highly porous microstructures were obtained with increasing amounts of carbon.