Oxygen potential and defect structure of oxygen-excess pyrochlore Ce 2Zr 2O 7+ x

Abstract

High-temperature thermodynamic study of the oxygen-excess pyrochlore-type (P-type) cerium zirconate Ce 2Zr 2O 7+ x has been performed by electromotive force (EMF) method in combination with the structural study by room-temperature powder X-ray diffraction (XRD) method. For this purpose, we have developed an EMF measurement system: (Pt) air |Zr(Ca)O 2− x | Ce 2Zr 2O 7+ x (Pt). The oxygen potential ( g(O 2)) vs. oxygen nonstoichiometry ( x) and temperature ( T) relations of P-type Ce 2Zr 2O 7+ x were elucidated. The g(O 2) vs. x relation of Ce 2Zr 2O 7+ x was controlled and measured at 1078 K over 0< x≤0.75 by applying the Coulomb titration method. The g(O 2) vs. temperature ( T) relation was also measured for each x by performing the temperature scan down to 793 K (793≤ T≤1078 K). It was found that the isothermal g(O 2) vs. x curves exhibit a terrace around x=0.5 for the measured temperature range. The powder XRD results showed that Ce 2Zr 2O 7+ x maintained its single pyrochlore-type structure all over 0< x<1 below 1078 K. The lattice parameters ( a 0) in this system were found to decrease almost linearly with x over 0< x≤1.