Synthesis by spark plasma sintering of a novel protonic/electronic conductor composite: BaCe0.2Zr0.7Y0.1O3−δ /Sr0.95Ti0.9Nb0.1O3−δ (BCZY27/STN95)
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A novel two-phase ceramic composite (cercer) material consisting of a solid solution of barium cerate and -zirconate doped with yttrium (BaCe0.2Zr0.7Y0.1O3−δ : BCZY27), together with niobium-doped strontium titanate (Sr0.95Ti0.9Nb0.1O3−δ : STN95), has been synthesized by solid-state reaction and sintered conventionally (CS) at 1350–1500 °C, as well as by spark plasma sintering (SPS) at 1300–1350 °C. CS samples were porous and exhibited high degrees of inter-phase reaction. Nickel oxide sintering aids did not improve CS sample density. In contrast, samples made by SPS were significantly denser (>95 %) and showed less reaction between phases. A pseudo-optimum SPS profile was developed, accounting for the effects of thermal expansion mismatch between BCZY27 and STN95. X-ray diffraction indicated secondary phases exist, but there was no indication of their presence at grain boundaries based on thorough study of these regions with high-resolution transmission electron microscopy and selective area electron diffraction. We thus suggest that these phases are present as independent grains in the bulk. It is believed these secondary phases inhibit electronic conductivity in the composite.
KeywordsSelective Area Electron Diffraction Spark Plasma Sinter Selective Area Electron Diffraction Pattern Conventional Sinter HAADF Image
The work was supported in part by internal funds from the Technical University of Denmark (DTU) under the Proton Conducting Fuel Cells (PCFC) Project, and by the Renewable Energy Materials Research Science and Engineering Center at the Colorado School of Mines under National Science Foundation Grant No. DMR-0820518. The authors are grateful to Ngo Van Nong at DTU for invaluable discussions on designing and implementing the SPS profiles. The SPS resources and supplies were provided by funds from the OTE-POWER Project through the Danish Council for Strategic Research under Contract No. 10-093971, and from the Novel Thermoelectric Power Generator Project through the Copenhagen CleanTech Cluster. The authors gratefully acknowledge support from the Swedish Energy Agency, Project No. 32939-1. Special thanks are also due to Finn Willy Poulsen at DTU for interpretation of XRD data on the SPS samples.
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