Influence of nano-structural feature on electrolytic properties in Y₂O₃ doped CeO₂ system

Abstract

. TEM observation gives us message that the size of coherent micro-domain with ordered structure would closely relate to the electrolytic properties such as conductivity and activation energy in the specimens. It was concluded that a control of micro-domain size in nano-scale in Y 2 O 3 doped CeO 2 system was a key for development of high quality solid electrolyte in fuel cell application. q

Oxygen-vacancy ordering in lanthanide-doped ceria: Dopant-type dependence and structure model

“…Though the measured conductivity includes contributions of both the grain boundaries and the bulk, it is believed that the decrease in conductivity is mainly due to the change in bulk conductivity because the grain size, and thereby the density of grain boundary, is similar in different samples. Specifically, as suggested in previous studies, [8][9][10][11][12] this decrease can be explained by the enhanced interaction between the oxygen vacancies and the segregated dopant cations in some regions named microdomains or nanosized domains. In addition, the oxygen-vacancy ordering may also affect the ionic conductivity.…”

“…Besides clusters of defects, the development of nanosized domains with increasing doping level was reported in doped ceria. [8][9][10][11] It has been demonstrated that diffuse scatterings and extra reflections on SAED patterns can be attributed to the formation of these domains. Furthermore, the studies of energyfiltering TEM ͑EFTEM͒ and high-angle annular dark-field scanning TEM ͑HAADF-STEM͒ have separately shown that these domains have higher dopant concentration than their matrix.…”

“…[2][3][4] However, in heavily doped ceria, nanosized domains can form and give negative impacts on the ionic conduction. [8][9][10][11] These domains have higher dopant concentrations than the matrix and could provide deep traps for the oxygen vacancies. 10,12 As a result of the domain formation, the advantage of the dopant having an optimum radius disappears with increasing the doping level.…”

Direct evidence of dopant segregation in Gd-doped ceria

“…5 It is also reported that lattice distortion in heavily doped ceria can be ascribed to conductivity decrease. 6 Recently, investigations elucidated that nanodomains widely observed in rare-earth ͑Y, 7 La, 8 Sm, 9,10 Gd, 9,11 Tb, 12 Dy, 10,13 Ho, 14 and Yb 9,10 ͒ doped ceria, could be responsible for the conductivity decrease. The nanodomains, with local ordered structures, can reduce the mobility of oxygen vacancies, leading to a decrease in ionic conductivity.…”

Oxygen vacancy ordering in heavily rare-earth-doped ceria

“…[2][3][4] However, in heavily doped ceria, nanosized domains can form and impact the ionic conductivity. [8][9][10][11] As a consequence, the advantage of the dopant with optimum radius disappears with increasing doping concentration. As shown in a comparative study of Gd-and Y-doped ceria, 12 conductivities in orders of GdϾ Y and GdϽ Y were observed at doping concentrations lower and higher, respectively, than 20-25 at.…”