Electrical conductivities of nano ionic composite based on yttrium-doped barium zirconate and palladium metal

Here we report on the structure and electrical properties of a protonic composite ceramic fabricated from yttrium-doped barium zirconate, BaZr0.85Y0.15O3 − δ (BZY15) as the major matrix phase with 2 wt.% palladium (Pd) as the minor dispersed phase. To synthesize the composite, BZY15 powder was first prepared by polymeric gelation followed by Pd incorporation via liquid impregnation from nitrate salt, producing green pellets by hydraulic dry pressing which were then sintered at 1600 °C. As sintered, most if not all of the Pd remained dispersed/dissolved within the BZY15 structure, yielding only a negligible effect on total conductivity (although the grain-bulk conductivity was enhanced in the Pd-loaded sample). In order to exsolve the Pd from the BZY15 structure and create a protonic/Pd-metal composite, several samples were reduced at 1000 °C for 24 h in dry 5% H2 (“highly reducing conditions”) or reduced at 650 °C for 24 h in wet 5% H2 (“modestly reducing conditions”). For the highly reduced samples, both large Pd particles ~ 1 μm (mixed with BZY15 grains) and small Pd particles ~ 20 nm (in some grain boundary regimes) were found and the conductivity was increased by a factor of ~ 1.5 times compared to the pure control. On the other hand, the modestly reduced samples, which only resulted in Pd nanoparticles ~ 5–10 nm in size, showed a conductivity increase factor of 2.7 compared to the same pure control.