Partial Conductivities and Chemical Diffusivities of Multi-Ion Transporting BaZr_xCe_0.85-xY_0.15O_3-δ(x = 0, 0.2, 0.4 and 0.6)

Abstract

BaZr x Ce 0.85-x Y 0.15 O 3-δ (BZCY); x = 0-0.6, were synthesized by a solid state reaction method. The phase composition of calcined powders was analyzed by powder X-Ray diffraction (XRD), which showed an orthorhombic lattice for BaCeY 0.15 O 3-δ (BZCY0), BaZr 0.2 Ce 0.65 Y 0.15 O 3-δ (BZCY20) and BaZr 0.4 Ce 0.45 Y 0.15 O 3-δ (BZCY40), and a cubic lattice for BaZr 0.6 Ce 0.25 Y 0.15 O 3-δ (BZCY60), indicating a transition from orthorhombic to cubic lattice with increasing Zr content. The defect chemical analysis of BZCY system was performed in order to analyze their charge and mass transport properties and the solutions of analytical defect equations were obtained in terms of various defect concentrations to calculate the partial conductivities and transport numbers of various charge carriers. The electrical conductivity was monitored by 4-probe dc-conductivity measurement with respect to the changes in oxygen partial pressure (pO 2 ) and water vapor pressure (pH 2 O) at different temperatures. The electrical conductivity relaxation (ECR) during oxidation/reduction in −2.4<log(pO 2 /atm)<−0.6 range at a fixed pH 2 O, and during hydration/dehydration in air in −3.3<log(pH 2 O/atm)<−2.3 range was recorded, and the surface exchange coefficients and chemical diffusivities of oxygen and hydrogen were calculated from Fick's second law by nonlinear least squares fitting of the conductivity data.