Dielectric relaxation properties of nanostructured Ce0.8Gd0.1Pr0.1O2−δ material at intermediate temperatures
TL;DR: The dielectric relaxation behavior of the fluorite structured nanocrystalline Ce0.8Gd0.1O2−δ compound was studied in the temperature range of 200-550 °C.
Abstract: The dielectric relaxation behavior of the fluorite structured nanocrystalline Ce0.8Gd0.1Pr0.1O2−δ compound was studied in the temperature range of 200–550 °C. Two different types of relaxation processes were observed corresponding to (1) defect pairs such as (PrCe′–VO)• and (GdCe′–VO)• and (2) the trimers such as (PrCe′–VO••–GdCe′). The correlation between ionic conduction and the dielectric properties of the nanocrystalline material is discussed. Very low values of the migration energy and association energy of the oxygen vacancies are observed, which are 0.42 and 0.03 eV, respectively. The obtained value of association energy agrees well with the theoretical prediction on doubly doped ceria.
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TL;DR: The present AC impedance analysis is consistent with the ab initio theoretical analysis of Li-excess garnets that showed two conduction paths for Li ion conduction with different activation energies.
Abstract: The fundamental electrical transport properties including ionic conductivity, dielectric constants, loss tangent, and relaxation time constants of Li-excess garnet-type cubic (space group Iad) Li5+2xLa3Ta2−xYxO12 (x = 0.25, 0.5 and 0.75) have been studied in the temperature range of −50 to 50 °C using electrochemical AC impedance spectroscopy. A correlation has been established between the excess Li content and the Li+ ion migration pathways. The loss tangent (tan δ) for all samples exhibits a relaxation peak corresponding to the dielectric loss because of dipolar rotations due to Li+ migration. Comparing the modulus analysis of Li-excess garnets with fluorite-type oxygen ion conductors, we propose the local migration of Li+ ions between octahedral sites around the “immobile” Li+ ions in tetrahedral (24d) sites. In the samples with x = 0.25 and 0.5, Li+ ions seem to jump from one octahedral (96h) site to another bypassing the tetrahedral (24d) site between them (path A), both in local and long-range order migration processes, with activation energies of ∼0.69 and 0.54 eV, respectively. For the x = 0.75 member, Li+ ions exhibit mainly long-range order migration, with an activation energy of 0.34 eV, where the Li hopping between two octahedral sites occurs through the edge which is shared between the two LiO6 octahedra and a LiO4 tetrahedron (path B). The present AC impedance analysis is consistent with the ab initio theoretical analysis of Li-excess garnets that showed two conduction paths (A and B) for Li ion conduction with different activation energies.
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TL;DR: In this paper, the effect of trivalent cations on the reducibility of CeO2 was investigated and the most stable configuration and the relative attraction between dopant cations and oxygen vacancies were determined.
Abstract: The doping of CeO2 with trivalent cations is a common technique for enhancing ionic conductivity in electrolytes for solid oxide fuel cell applications. However, the local defect structure in these materials is yet to be fully explored. Furthermore, many studies have overlooked the effect of the dopants on the reducibility of CeO2, which is important as electronic conductivity can short-circuit the fuel cell. Density functional theory (DFT)+U calculations have been performed on a series of CeO2 systems doped with trivalent cations. The most stable configuration and the relative attraction between dopant cations and oxygen vacancies were determined, and it was found that the defect structure is principally dependent on the ionic radius of the dopant cations. The reduction energy was found to be dependent on the structure around the dopants but did not vary significantly between dopants of similar ionic radii. From these results, it is possible to suggest which trivalent cations would be most suitable to en...
65 citations
TL;DR: Gd and Nd co-doped ceria nanocrystalline materials [Ce 09 Gd 01-x Nd x O 195 (0.≤,x,≤,01)] were successfully prepared through citrate-nitrate auto-ignition method by Rietveld refinement of the X-ray diffraction profiles was performed to get detailed microstructural information as mentioned in this paper.
49 citations
TL;DR: In this paper, electrical and dielectric properties of the nanocrystalline GDC materials co-doped with CoO (by deposition precipitation method) were studied in the temperature range of 150-600°C.
37 citations
TL;DR: In this article, the ionic conductivity of rare earth-doped ceria has been investigated in Solid Oxide Fuel Cells (SOFCs) and different opinions regarding the effect of these factors on ionic performance have been expressed.
34 citations
References
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TL;DR: In this article, the physical, chemical, electrochemical and mechanical properties of pure and doped ceria, predominantly in the temperature range from 200 to 1000°C, are investigated.
1,870 citations
TL;DR: Grain boundary conductivities were determined by complex impedance measurements (1-106 Hz) on high-purity ceramics prepared by the alkoxide synthesis and on less pure Ceramics obtained from a commercial powder as discussed by the authors.
403 citations
TL;DR: In this paper, the effect of the grain boundary effect on dc ionic conductivity was studied for ceria ceramics doped with trivalent dopants (Y3+, Gd3+, and La3+).
Abstract: The “grain-boundary effect,” which leads to a greatly reduced dc ionic conductivity due to the presence of a blocking layer in the vicinity of the grain boundaries, is studied in detail for ceria ceramics doped with various trivalent dopants (particularly Y3+, Gd3+, and La3+). The effects of porosity, of sintering time, and of dopant size and dopant concentration are investigated. Finally, it is shown that the grain-boundary effect virtually disappears when nearly silicon-free starting materials are used.
288 citations
TL;DR: In this article, the ionic conductivity of dilute CeO 2 :M 2 O 3 solid solutions has been investigated for four different dopants M 3+, viz., La 3+, Gd 3+, Y 3+, and Sc 3+.
216 citations
TL;DR: In this article, the ac electrical behavior of sintered polycrystalline CeO 2 :CaO and CY 2 :Y 2 O 3 solid electrolytes is studied and it is shown that the activation enthalpy for the grain-boundary conductivity is substantially higher than that of the lattice conductivity.
181 citations