Exploring the oxygen vacancies and electrical properties in pyrochlore-type Ca_1.46Ti_1.38Nb_1.11O₇

Abstract

Pyrochlore-type oxides are considered potential oxide-ion conductors due to their high concentration of oxygen vacancies in the unit cell. In this work, the pyrochlore-type Ca_1.46Ti_1.38Nb_1.11O₇ was synthesized and its crystal structure was characterized by Rietveld refinement. A high oxygen vacancy concentration in the material was confirmed by thermogravimetry (TG) and X-ray photoelectron spectroscopy (XPS). TG, XPS, and electron paramagnetic resonance collectively demonstrated the change in oxygen vacancy concentration of the material following atmosphere switching. The electrical properties of Ca_1.46Ti_1.38Nb_1.11O₇ under different atmospheres were characterized by electrochemical impedance spectroscopy. The conductivity of Ca_1.46Ti_1.38Nb_1.11O₇ was 4.20 × 10^-2 S cm^-1 in 5% H₂/Ar, 9.22 × 10^-3 S cm^-1 in Ar and 2.92 × 10^-5 S cm^-1 in air at 900 °C. Bond valence site energy calculations indicated that oxide ions diffuse three-dimensionally in Ca_1.46Ti_1.38Nb_1.11O₇. Ca_1.46Ti_1.38Nb_1.11O₇ is a promising solid electrolyte for oxygen sensors. This work investigates the structure-property relationship between oxygen vacancies and conductivity in pyrochlore-type oxides.

Keywords

Ionic conductor / conductivity / solid electrolyte / solid oxide fuel cells / ion migration

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