Understanding of dynamics of electrical processes in nanostructured Gd-doped ceria

Abstract

Gd-doped ceria (Ce0.90Gd0.1O2-δ) (GDC) nanorods were synthesized by microwave-assisted precipitation route. The morphology is confirmed by SEM and TEM and structure by XRD. Compaction and net-product development of the samples for electrical characterization, two modes of heating was used viz microwave (MS-GDC) and conventional (CS-GDC). After sintering, the microstructure of CS-GDC shows round shape grains of highly compacted pellet while MS-GDC sustains rod-shape microstructure of grains. Complex impedance spectra revealed that MS-GDC exhibits more ionic conductivity than CS-GDC and grain boundary effect is dominant over grain interior. To get more in-depth on influence of shape of grains on ion conducting mechanism; the dynamics of electrical processes are understood by charge relaxation process at grains and grains boundaries. Dielectric functions such as dielectric permittivity (ε’), loss tangent (tan δ) and electric modulus (M”) are used to reveal charge relaxation time. The charge relaxation times are observed five orders higher in CS-GDC than MS-GDC. Ion association and migration energy are obtained lower in rod-shape grain. Grain shape influence on the activation energy can be speculated as one dimensional extension in rod-shape grain as compared to round grain gives rise to expansion in ordered structure of lattice and thus the ordering of oxygen vacancies within the grain. This results out (i) expansion of conduction pathway across the grain boundary, (ii) long range motion of oxygen vacancies in grains and (iii) shorten the relaxation time. This work identifies the potential of 1D nanostructure oxy-ion conductors; as promising electrolyte materials for ITSOFCs.