The microstructure and electrical properties of low-resistance contacts to YBa sub 2 Cu sub 3 O sub 7- delta ceramics

Contacts with resistivities < =10 exp -8 Omega cm exp 2 , at temperatures below the T sub c of the underlying YBCO material, have been formed by incorporating gold wires into silver contact pads in a single heat treatment. Voltage-current characteristics of these contacts show superconducting behaviour. Microstructural cross-sections show an Ag/Au alloy with an Ag:Au atomic ratio of 3:1. Contacts made by applying wires after the silver heat treatment, which do not form an Ag/Au alloy, show residual resistances below T sub c of approx0.5-50 m Omega . Susceptibility and resistivity measurements were not suitable for critically differentiating between contact methods or treatment temperatures.