LOW-TEMPERATURE EIS MEASUREMENTS ON HIGH-TC SUPERCONDUCTOR SOLID ELECTROLYTE INTERFACES

Electrochemical impedance spectroscopy (EIS) was carried out in the system YBa2Cu3O7-δ/ RbAg4I5 in the temperature range 19 K ≤ T≤ 298 K, Reliable impedance data over the frequency range 1 Hz ≤ f ≤ 105 Hz could be obtained using a two-probe polarization technique under potentiostatic control with perturbation amplitudes of 5 mV ≤ ΔE≤ 3 V. Using a complex non-linear fit procedure, the ohmic resistance Rω, the charge transfer resistance Rt, and the double layer capacitance CDL were determined. The following phenomena are reflected by the temperature dependences of these parameters: theβ-γ phase transition of RbAg4I5 at T = 120±2 K by rΩ and cDL, a change of the double layer structure at Tc by CDL, and a change of the charge transfer mechanism around Tc by Rt. The charge transfer resistance and the double layer capacitance exhibit significant minima at the critical temperature Tc=92±2 K and become nearly temperature independent below Tc. This extraordinary behaviour is discussed in terms of Cooper pair tunneling and of a change in the double layer structure leading to an enhancement of the charge transfer kinetics of the Faradaic electrode reaction. © 1990.