Thermodynamic stability, oxygen content, defect structure and related properties of YBaCo4 − xZnxO7 + δ (x = 0-3) oxides

Oxygen nonstoichiometry and thermodynamic stability of Zn-doped YBaCo4 − xZnxO7 + δ oxides were investigated by solid state coulometric titration and EMF-method, respectively. As a result, significant zinc doping was shown to increase the stability of YBaCo4 − xZnxO7 + δ oxides in oxidizing atmosphere. However enrichment of YBaCo4 − xZnxO7 + δ oxides by zinc results in increasing their reducibility since the low pO2 stability limit shifts towards higher pO2 values upon doping. Substitution of zinc for cobalt in YBaCo4 − xZnxO7 + δ oxides was also found to narrow their oxygen homogeneity region. Total conductivity and Seebeck coefficient of YBaCo4 − xZnxO7 + δ oxides were measured simultaneously using 4-probe dc-method. The defect structure of YBaCo4 − xZnxO7 + δ oxides was successfully analysed using Kröger-Vink approach. The data on oxygen nonstoichiometry, total conductivity and Seebeck coefficient of the thermodynamically stable YBaCo4 − xZnxO7 + δ (x = 0, 1) oxides were found to be quite consistent with the proposed model of their defect structure.