High-temperature superconductor materials for contact layers in solid oxide fuel cells: I. Sintering behavior and physical properties at operating temperatures

The superconducting materials Bi2Sr2CaCu2O8+x, and Bi2Sr2CuO6+x were identified as possible candidates for contact layer materials between the perovskite-type ceramic cathode and the metallic interconnector for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The two compounds were synthesized by solid-state reaction and citrate complexation techniques. Densification experiments were performed in air at different temperatures. It was found that the pressed pellets fabricated from both the phases had undergone shape changes due to swelling at temperatures above 800 degreesC. Since the processes of volume expansion and crystallization were found to compete with the sintering process, it was expected to be very difficult to achieve compact layers from these materials. The conductivity measurements indicated metallic behavior of both phases and rather low conductivity values fur application as a contact layer in IT-SOFC. Dilatometric experiments were also carried out on these materials to measure their thermal expansion coefficients. The properties of commercial-grade YBa2Cu2O7-x were also investigated for comparison. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Lm! All rights reserved.