Optical evaluation of Ni, Fe and Co impurity content in Y-doped barium zirconate

Y-doped BaZrO₃ (BZY) is a promising candidate for the electrolyte material of proton conducting fuel cell (PCFC). The impurity concentrations of Ni, Co, and Fe are often of interest in studies of cell processing because the electrochemical performances and the sinterability remarkably depend on the concentrations. This work proposes a simple technique to quantify the dissolved Fe, Co, and Ni in BZY sintered bodies by evaluating the color in the L^⁎a^⁎b^⁎ color space. Colorimetric measurements revealed a roughly linear relationship between L^⁎ and the logarithm of Fe, Co, and Ni concentrations in the dilute range from 0.001 to 0.1 at.%, providing an empirical calibration curve. L^⁎ values also depend on the raw BZY powders used as the starting material and the sintering procedure, resulting in variations in relative density, Ba deficiency and excess of the sintered body. Therefore, when applied to a series of sintered bodies with consistent starting material and same processes, this calibration curve is reliable.