Resistivity and Microstructure of Joint-Interface between YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7−δ</SUB> and Indium Alloys

In order to improve contact resistance between high-Tc superconducting ceramics YBa2Cu3O7−δ and Indium or Indium alloys, interfacial microstructures of the contacts were studied with respect to contact resistance.YBa2Cu3O7−δ ceramics (YBCO) was prepared by a solid state reaction and sintering of the dry powders at 1223 K. The YBCO/Indium or YBCO/Indium alloy interface was made by soldering below 623 K under ultrasonic exciting loading. In the contact of YBCO/Indium, the microstructure and compounds near the interface were analyzed by SEM-EDX, TEM and XRD, and it was observed that the reacted layer at the interface consists of In2O3 and Ba-In oxides. It is thought that these compounds give a comparatively high contact resistivity of 10−6Ω·m2 order.Then, in order to make lower the contact resistivity, ten kinds of binary alloys with additives of Pb, Sn and Cd, etc. were used to join with YBCO. Among these alloys, the contact resistivity in the YBCO/In-Cd interfacial layer was very low which is about 10−9∼10−8Ω·m2. One of the compounds in this layer was identified as CdO. The resistivity of CdO was about 10−3Ω·m, much lower than that of In2O3. Therefore we considered that low contact resistance of the YBCO/In-Cd interface is due to the formation of CdO at the reacted layer.