Effect of sintering temperature on microstructure, chemical stability, and electrical properties of transition metal or Yb-doped BaZr _0.1 Ce _0.7 Y _0.1 M _0.1 O _3-δ (M = Fe, Ni, Co, and Yb)

Perovskite-type BaZr _0.1 Ce _0.7 Y _0.1 M _0.1 O _3-δ (M = Fe, Ni, Co, and Yb) (BZCY-M) oxides were synthesized using the conventional solid-state reaction method at 1350-1550°C in air in order to investigate the effect of dopants on sintering, crystal structure, chemical stability under CO2 and H ₂ S, and electrical transport properties. The formation of the single-phase perovskite-type structure with an orthorhombic space group Imam was confirmed by Rietveld refinement using powder X-ray diffraction for the Fe, Co, Ni, and Yb-doped samples. The BZCY-Co and BZCY-Ni oxides show a total electrical conductivity of 0.01 and 8 × 10 ^-3 S cm ^-1 at 600°C in wet H ₂ with an activation energy of 0.36 and 0.41 eV, respectively. Scanning electron microscope and energy-dispersive X-ray analysis revealed Ba and Co-rich secondary phase at the grain-boundaries, which may explain the enhancement in the total conductivity of the BZCY-Co. However, ex-solution of Ni at higher sintering temperatures, especially at 1550°C, decreases the total conductivity of the BZCY-Ni material. The Co and Ni dopants act as a sintering aid and form dense pellets at a lower sintering temperature of 1250°C. The Fe, Co, and Ni-doped BZCY-M samples synthesized at 1350°C show stability in 30 ppm H ₂ S/H ₂ at 800°C, and increasing the firing temperature to 1550°C, enhanced the chemical stability in CO ₂ /N ₂ (1:2) at 25-900°C. The BZCY-Co and BZCY-Ni compounds with high conductivity in wet H ₂ could be considered as possible anodes for intermediate temperature solid oxide fuel cells.