Synthesis by spark plasma sintering of a novel protonic/electronic conductor composite: BaCe_0.2Zr_0.7Y_0.1O_3−δ /Sr_0.95Ti_0.9Nb_0.1O_3−δ (BCZY27/STN95)

A novel two-phase ceramic composite (cercer) material consisting of a solid solution of barium cerate and -zirconate doped with yttrium (BaCe_0.2Zr_0.7Y_0.1O_3−δ : BCZY27), together with niobium-doped strontium titanate (Sr_0.95Ti_0.9Nb_0.1O_3−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.