Effect of grain interior and grain boundaries on transport properties of Sc-doped CaHfO3

Abstract

Abstract A novel CaHf0.9Sc0.1O3-α perovskite protonic conductor was prepared and the effects of grain interior and grain boundaries on the carriers’ transport properties were systematically investigated via defect chemistry theory and H2/H2O concentration cell. The CaHf0.9Sc0.1O3-α exhibited an orthorhombic distortion and the standard molar hydration enthalpy of CaHf0.9Sc0.1O3-α was found to be −44 kJ/mol. The migration activation energies for conduction of protons, oxygen vacancies, and holes in CaHf0.9Sc0.1O3-α under oxygen were 0.81 eV, 1.68 eV, and 1.79 eV, respectively. The proton concentration in CaHf0.9Sc0.1O3-α grains was higher than that in the grain boundaries, while in contrast, the oxygen vacancy concentration in grains was lower than that in the grain boundaries. The proton conduction through CaHf0.9Sc0.1O3-α was dominant in Ar as well as reductive atmospheres at 500–800 °C, where the hole conductivity ( σ h · ) and hole transport number ( t h · ) remarkably increased with increasing oxygen partial pressure. The relative transport number results reveal that the grain interior of CaHf0.9Sc0.1O3-α is better suited than grain boundaries to block the hole transport, and grains interior could be used to improve the protons transport number t OH O · .