The crystallization effects of boron (B) powder on the phase, full width at half maximum (FWHM) values, and critical properties were investigated for in-situ reacted MgB2 bulk superconductors. The semi-crystalline B powder was heat-treated at different temperatures of 1000, 1300 and 1500˚C for 5 hours in an Ar atmosphere. Then, using as-received and heat-treated B powders, the MgB2 samples were prepared at 600˚C for 40 hours in an Ar atmosphere. As the heat-treatment temperature of the B powder increased, both the particle size of the B powder and crystalline phase increased. In the case of MgB2 samples using B powders heat-treated at above 1300˚C, unreacted magnesium (Mg) and B remained due to the improved crystallinity of the B powder. As the heat-treatment temperature of B powder increased, the critical current density of MgB2 decreased continuously due to the reduction of grain boundary density and superconducting volume caused by unreacted Mg and B.

GdBa2Cu3O7-y(Gd123) powders were synthesized by the solid-state reaction method using Gd2O3 (99.9% purity), BaCO3 (99.75%) and CuO (99.9%) powders. The synthesized Gd123 powder and the Gd123 powder with Gd2O3 addition (Gd1.5Ba2Cu3O7-y(Gd1.5)) were used as raw powders for the fabrication of Gd123 bulk superconductors. The Gd123 and Gd1.5 bulk superconductors were fabricated by sintering or a top-seeded melt growth (TSMG) process. The superconducting transition temperature (Tc,onset) of the sintered Gd123 was 93 K and the transition width was as large as 20 K. The Tc,onset of the TSMG processed Gd123 was 82 K and the transition width was also as large as 12 K. The critical current density (Jc) at 77 K and 0 T of the sintered Gd123 and TSMG processed Gd123 were as low as a few hundreds A/cm2. The addition of 0.25 mole Gd2O3 and 1 wt.% CeO2 to Gd123 enhanced the Tc, Jc and magnetic flux density (H) of the TSMG processed Gd123 sample owing to the formation of the superconducting phase with high flux pinning capability. The Tc of the TSMG processed Gd1.5 was 92 K and the transition width was 1 K. The Jcs at 77 K (0 T and 2 T) were 3.2×104 A/cm2 and 2.5×104 A/cm2, respectively. The H at 77 K of the TSMG-processed Gd1.5 was 1.96 kG, which is 54% of the applied magnetic field (3.45 kG).

(Y123) powders for the fabrication of bulk superconductors were synthesized by the powder reaction method using (99.9% purity), (99.75%) and CuO (99.9%) powders. The raw powders were weighed to the cation ratio of Y:Ba:Cu=1:2:3, mixed and calcined at in air with intermediate repeated crushing steps. It was found that the formation of Y123 powder was more sensitive to reaction temperature than reaction time. The calcined Y123 powder and a mixture of (Y123 + 0.25 mole + 1 wt.% , (Y1.5)) were used as raw powders for the fabrication of poly-grain or single grain superconductors. The superconducting transition temperature () of the sintered Y123 sample was 91 K and the transition width was as large as 11 K, whereas the of the melt-grown Y1.5 sample was 90.5 K and the transition width was 3.5 K. The critical current density () at 77 K and 0 T of the sintered Y123 was 700 , whereas the of the top-seeded melt growth (TSMG) processed Y1.5 sample was . The magnetic flux density (H) at 77 K of the TSMG-processed Y123 and Y1.5 sample showed the 0.53 kG and 2.45 kG, respectively, which are 15% and 71% of the applied magnetic field of 3.5 kG. The high H value of the TSMG-processed Y1.5 sample is attributed to the formation of the larger superconducting grain with fine Y211 dispersion.