Synthesis and characterisation of ceramic proton conducting perovskite-type multi-element-doped Ba_0.5Sr_0.5Ce_{1−x−y−z}Zr_xGd_yY_zO_3−δ (0 < x < 0.5; y = 0, 0.1, 0.15; z = 0.1, 0.2)

This study addresses the influence of A-and B-site co-doping on the chemical and electrical properties of perovskite-type Ba_0.5Sr_0.5Ce_{1−x−y−z}Zr_xGd_yY_zO_3−δ (0 < x < 0.5; y = 0, 0.1, 0.15; z = 0.1, 0.2). The powders synthesised at 1450 °C through solid state (ceramic) reaction showed relative density greater than 94% by Archimedes method, and is supported by dense microstructure using scanning electron microscopy images. The effect of doping electronegative elements on the A-and B-site on chemical stability is exemplified by dopant dependent chemical stability under CO₂ and water vapour. Thermogravimetric analysis (TGA) of the powdered samples under CO₂: N₂ (1:1) showed variation in weight gain with respect to doping element concentration in Ba_0.5Sr_0.5Ce_{1−x−y−z}Zr_xGd_yY_zO_3−δ, revealing the improved chemical stability of Ba_0.5Sr_0.5Ce_0.6Zr_0.2Gd_0.1Y_0.1O_3−δ and Ba_0.5Sr_0.5Ce_0.5Zr_0.3Gd_0.1Y_0.1O_3−δ. Excellent chemical stability under water vapour at 90 °C for 24 h was observed for all the investigated compositions. However, extended exposure time of 168 h lead to the appearance of a small amount of Ba(OH)₂, as observed from the powder X-ray diffraction patterns and TGA analysis after stability tests. The electrical conductivity measurements by ac impedance spectroscopy under dry and humid atmospheres revealed the proton conductivity. Among the samples investigated in this work, Ba_0.5Sr_0.5Ce_0.6Zr_0.2Gd_0.1Y_0.1O_3−δ (BSCZGY3) showed the highest electrical conductivity of ∼10⁻³ S/cm at 700 °C in air/3% H₂O and H₂/3% H₂O.