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

Abstract

( Nd 0.7 Yb 0.3)2 Zr 2 O 7 and (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 (0 < x ≤ 0.25) ceramics have been synthesized by pressureless sintering by tailoring the chemical compositions. Microstructure and electrical conductivity of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and AC impedance spectroscopy. ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 ceramic exhibits a mixed crystal structure of defect fluorite and pyrochlore. After doping with Sm 3+ cations, the structure changes from a mixed type of ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 to a single pyrochlore type of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7, as the addition of Sm 3+ reduces the difference in ionic radius between Nd 3+ and Yb 3+. However, (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 ceramics contain the localized short-range disorder despite the structural order overall in the pyrochlore. The measured total conductivities of (( Nd 0.7 Yb 0.3)1-x Sm x)2 Zr 2 O 7 obey the Arrhenius relation. Doping of Sm 3+ enhances the electrical conductivity of ( Nd 0.7 Yb 0.3)2 Zr 2 O 7 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.