Effects of Residual Carbon on Superconducting Properties of Y123 Melt-Solidified Bulks

Effects of residual carbon on the carrier-doping level and resulting superconducting properties were systematically investigated for Y123 melt-solidified bulks containing different amounts of carbon. The dependence of T_c on annealing temperature in flowing oxygen was almost identical among each sample from underdoped to optimally doped state and all the samples exhibited highest T_c when they were annealed at ~500degC. On the other hand, the carbon-free samples showed apparently lower T_c than those of the carbon containing samples in the overdoped state. Especially, a sample fabricated in air showed the quite small decrease in T_c by overdoping, suggesting that residual carbon suppresses effective carrier doping to be heavily overdoped state for Y123 melt-solidified bulks. Therefore, Y123 melt solidified bulk with less residual carbon exhibited higher H_irr and J_c properties at the overdoped state.