Ａｇ２Ｏ添加ＹＢＣＯ超伝導セラミックスの接合性と超伝導特性

Abstract

Effects of silver oxide additions on the bonding and superconducting properties of YBCO superconductors were studied. The YBCO superconductor ceramics were diffusion bonded with the parameters of 1223 K for 1 hour under the pressure of 2. 4 kPa in air. Thermal analysis and SEM/EDX analysis showed that during the bonding process, Ag2O additive was thermo-chemically decomposed and diffused into YBCO ceramics. The Ag did not react with the YBCO during the bonding processes and existed as the pure Ag in the YBCO matrix. With the increase of Ag2O content until 10 mass%, the strength of joints and critical current density Jc were increasing, but over addition of Ag2O made Jc decrease, although the critical transition temperature was nearly constant with the increase of Ag2O content.It was believed that during the bonding processes, thermochemically decomposed Ag diffused into the YBCO and filled into the voids in bonded surfaces, which could make a good contact between the bonded surfaces during the bonding processes, so the strength got increased. However, over addition of Ag2O would cause the decreasing in fraction of superconducting constitution, then the superconductivity became worse. It was feasible to bond the YBCO superconductors when the Ag2O was properly added. The diffusion bonding thermal cycle would not affect the crystal structure of the YBCO.