Exploring the oxygen vacancies and electrical properties in pyrochlore-type Ca1.46Ti1.38Nb1.11O7

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 Ca1.46Ti1.38Nb1.11O7 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 Ca1.46Ti1.38Nb1.11O7 under different atmospheres were characterized by electrochemical impedance spectroscopy. The conductivity of Ca1.46Ti1.38Nb1.11O7 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 Ca1.46Ti1.38Nb1.11O7. Ca1.46Ti1.38Nb1.11O7 is a promising solid electrolyte for oxygen sensors. This work investigates the structure-property relationship between oxygen vacancies and conductivity in pyrochlore-type oxides.