Influence of Sm3+ doping on microstructure and electrical properties of ((Nd0.7Yb0.3)1-xSmx)2Zr2O7

(Nd0.7Yb0.3)2Zr2O7 and ((Nd0.7Yb0.3)1-xSmx)2Zr2O7 (0 < x ≤ 0.25) ceramics have been synthesized by pressureless sintering by tailoring the chemical compositions. Microstructure and electrical conductivity of ((Nd0.7Yb0.3)1-xSmx)2Zr2O7 were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and AC impedance spectroscopy. (Nd0.7Yb0.3)2Zr2O7 ceramic exhibits a mixed crystal structure of defect fluorite and pyrochlore. After doping with Sm3+ cations, the structure changes from a mixed type of (Nd0.7Yb0.3)2Zr2O7 to a single pyrochlore type of ((Nd0.7Yb0.3)1-xSmx)2Zr2O7, as the addition of Sm3+ reduces the difference in ionic radius between Nd3+ and Yb3+. However, ((Nd0.7Yb0.3)1-xSmx)2Zr2O7 ceramics contain the localized short-range disorder despite the structural order overall in the pyrochlore. The measured total conductivities of ((Nd0.7Yb0.3)1-xSmx)2Zr2O7 obey the Arrhenius relation. Doping of Sm3+ enhances the electrical conductivity of (Nd0.7Yb0.3)2Zr2O7 ceramic significantly, which is closely related to the variations in the concentration of oxygen vacancies at 48f sites, relatively low activation energy and high pre-exponential factor caused by the long-range order and short-range disorder.