Ionic conductivity of oxygen ions in YBa 2Cu 3O 7−x

Abstract

The ionic conductivity of oxygen ions in YBa 2Cu 3O 7−x has been measured at constant partial pressure of oxygen as a function of temperature between 300 and 500°C. A four-probe dc technique was applied with four oxygen-ion conducting electrodes. The electrodes, consisting of the phase sequence M/YBa 2Cu 3O 7−x/ZrO 2(+10% Y 2O 3) (with M=Pt or Au), were blocking for electrons. The samples were sintered in air at different temperatures between 875 and 950°C followed by a further annealing in air at 425°C for 5–10 h. Transition temperatures of superconductivity between 86 and 90 K (midpoint between onset and offset temperature) were found depending on the sintering temperature. The ionic conductivity of these samples decreases with increasing temperature of the usual high temperature thermal treatment. This influence on the ionic conductivity may be caused by corresponding changes of the nonstoichiometry within the metal sublattice during thermal treatment. In the temperature range 300–500°C, the oxygen-ion conductivity of YBa 2Cu 3O 7−x changes with increasing temperature from about 10 −5 to 1 (ohm cm) −1 in air. From an Arrhenius plot “activation” energies of 2.5–2.7 eV are determined for temperatures above 390°C and slightly lower values of 2.2±0.1 eV below 370°C. The results show that YBa 2Cu 3O 7−x, like many other oxides with the perovskite structure is a good ion conductor for O 2- ions in a medium temperature range. It operates well as an oxygen electrode in galvanic cells at relatively low temperatures.