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 identi fied as possible candidates for contact layer materials between the perovsk ite-type ceramic cathode and the metallic interconnector for intermediate-t emperature solid oxide fuel cells (IT-SOFCs). The two compounds were synthe sized by solid-state reaction and citrate complexation techniques. Densific ation experiments were performed in air at different temperatures. It was f ound that the pressed pellets fabricated from both the phases had undergone shape changes due to swelling at temperatures above 800 degreesC. Since th e processes of volume expansion and crystallization were found to compete w ith the sintering process, it was expected to be very difficult to achieve compact layers from these materials. The conductivity measurements indicate d metallic behavior of both phases and rather low conductivity values fur a pplication as a contact layer in IT-SOFC. Dilatometric experiments were als o carried out on these materials to measure their thermal expansion coeffic ients. The properties of commercial-grade YBa2Cu2O7-x were also investigate d for comparison. (C) 2001 Acta Materialia Inc. Published by Elsevier Scien ce Lm! All rights reserved.