Ag₂O添加YBCO超伝導セラミックスの接合性と超伝導特性

抄録

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 J_c were increasing, but over addition of Ag₂O made J_c 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.