Effect of Sr Deficiency on Electrical Conductivity of Yb-Doped Strontium Zirconate

The effect of Sr-deficiency on microstructure, phase composition and electrical conductivity of Sr_xZr_0.95Yb_0.05O_3-δ (x = 0.94-1.00) was investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and impedance spectroscopy. The samples were synthesized by a chemical solution method and sintered at 1600 °C. According to X-ray diffraction data, the samples with x = 0.96-1.00 were single-phase oxides possessing an orthorhombic perovskite-type structure; while zirconia-based minor phases arouse at x = 0.94, which was confirmed by the electron microscopy. Sr stoichiometry was shown to influence the electrical conductivity. The highest total and bulk conductivities, 6-10^-4 Scm^-1 and 3-10^-3 Scm^-1, respectively, at 600 °C in humid air (pH₂O = 3.2 kPa), were observed for the x = 0.98 composition. In the temperature range of 300-600 °C, the conductivity of the samples with x = 0.96-1.00 increased with the increase in humidity, which indicates a significant contribution of protonic defects to the charge transport. Electrical conductivity of Sr_xZr_0.95Yb_0.05O_3-δ was discussed in terms of the defect formation model and the secondary phases precipitation.