Grain boundary space charge modulation in BaZr0.8Y0.2-xMxO3−δ with transition metal (M= Ni, Co, Fe, and Zn) co-doping

Abstract

The higher grain boundary resistance of proton-conducting ceramic electrolytes such as BaZrO3 drops the total conductivity. In the present study, BaZr0.8Y0.2-xMxO3−δ electrolyte with various transition metals (M= Ni, Co, Fe, and Zn) with molar concentrations (x = 0.01, 0.03 & 0.05) were prepared by hydrothermal assisted precipitation method. The structural analysis, such as XRD and Raman, revealed the presence of the cubic perovskite phase of barium zirconate. The existence of space charge layer was confirmed by nonlinear behaviour of the grain boundary resistance on applying DC bias. The Mott–Schottky analysis performed at 200 °C in reducing atmosphere showed a reduction in barrier potential from 0.24 to 0.13 V upon the addition of the secondary dopants. The elastic energy minimization by dopant segregation and electrostatic interaction between the charged defects and dopants suppress the space charge layer. The transition metal dopant, especially Ni and Fe, segregates along the grain boundary and acts as the counterbalance for charged defects. Besides, Fe act as perfect sintering aid which leads to higher densification (>99%) as well as higher protonic conductivity of 21.2 mScm−1 at 600 °C. These results imply that the transition metal ions as co-dopant influence the space charge effect and the density of the barium zirconate electrolyte.