Grain Size Effect on Electrical and Dielectric Properties of the Nanostructured Dy-Doped Ceria ( Ce0.8Dy0.2O2 − δ )
01 Jun 2010-Journal of The Electrochemical Society (The Electrochemical Society)-Vol. 157, Iss: 6, pp 53
TL;DR: In this paper, the authors discussed the dielectric and electrical properties of the nanostructured Ce 0.8 Dy 0.2 O 2 −δ material with average grain sizes of 15, 35, and 58 nm.
Abstract: Electrical and dielectric properties, and their correlations were discussed in the nanostructured Ce 0.8 Dy 0.2 O 2―δ materials with average grain sizes of 15, 35, and 58 nm using the dielectric functions such as dielectric permittivity (e'), loss tangent (tan δ), and electric modulus (M"). The ionic transport mechanism varies with the grain size of the materials such that the material with an average grain size of 35 nm exhibited a higher value of ionic conductivity above 440°C (with σ = 8.96 × 10 ―4 S cm ―1 at 550°C), whereas the material with an average grain size of 15 nm shows higher value conductivity at lower temperatures. The oxygen vacancy in the material decreases with the decrease in grain size. The migration energy of oxygen ions also decreases with the decrease in grain size of the nanostructured Ce 0.8 Dy 0.2 O 2―δ material. The material with an average grain size of 35 nm shows a very low value association energy (i.e., 0.05 eV) compared to the others. At temperatures below 420°C, the local motion of oxygen vacancies around Dy +3 controls the conductivity of all the materials, and at higher temperatures, the conductivity in the materials with a larger grain size is mainly due to the long-range motion of vacancies.
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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.
Abstract: 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 Rietveld refinement of the X-ray diffraction profiles was performed to get detailed microstructural information of the prepared samples It had been found that with an increase of Nd concentration, the lattice parameter and average Ce O bond distance increased The average crystallite size, calculated from XRD was in good agreement with the transmission electron microscopy result It was observed that, co-doped ceria showed slightly higher conductivity than the single doped with the same dopant concentration The grain boundary conductivity was found to be higher than the grain interior conductivity The increase in dielectric loss tangent value and shifting of the peak frequency with temperature indicated a thermally activated relaxation process which was found corresponding to defect pairs The correlation between structural and dielectric properties of the samples was established
49 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.
Abstract: The rare–earth–doped ceria overcomes the difficulties of yttria–stabilized zirconia (YSZ) as an electrolyte in Solid Oxide Fuel Cells (SOFCs) due to its superior ionic conductivity in the intermediate temperature range. However, several factors such as synthesis process, sintering condition, dopant concentration, co–doping mechanism, dopant vacancy interaction, ionic radius of dopants, grain boundary, grain size, affect the ionic conductivity of the rare earth doped ceria. It is difficult to explain the ionic conductivity of rare–earth–doped ceria in terms of a single factor because there is a complex correlation among these factors. This review tries to find the complicated relationship between these factors. This work also reviews different opinions regarding the effect of these factors on ionic conductivity. The knowledge about the factors is vital to develop a better solid electrolyte for SOFCs. This work is an overview of the ionic conductivity of rare–earth–doped ceria in terms of the several affecting factors.
34 citations
TL;DR: In this paper, the optical properties were studied using FT-IR and UV-vis absorption spectra, which confirmed the presence of functional groups and chemical bonding in the material and the optical band gap was calculated from UVvis spectra and its value was found to decrease from 3.70 eV to 2.46 eV with increase in sintering temperature.
Abstract: Neodymium doped nanocrystalline ceria [Ce0.9Nd0.1O1.95] was prepared through citrate auto-ignition method. The prepared samples were sintered at five different temperatures starting from 400 °C up to 1200 °C. Rietveld׳s powder structure refinement analysis of XRD data confirmed the single phase cubic fluorite structure of the prepared samples with space group Fm 3 ¯ m and the obtained particle size and lattice parameter values were found to vary with sintering temperature from 6.68 nm to 39.51 nm and from 5.39077 A to 5.42317 A respectively. The optical properties were studied using FT-IR and UV–vis absorption spectra. The FT-IR spectra confirm the presence of functional groups and chemical bonding in the material. The optical band gap was calculated from UV–vis spectra and its value was found to decrease from 3.70 eV to 2.46 eV with increase in sintering temperature. The dc conductivity was found to be thermally activated and decreased with increase in sintering temperature. The nature of impedance spectra reveals the presence of both grain and grain boundary effect. The tangent loss exhibited the presence of relaxation peaks due to the presence of defect pair in the synthesized samples.
27 citations
TL;DR: In this paper, defect associates and their interactions with charge carriers, influencing the ion dynamics have been discussed for Gd3+ and Y3+ co-doped nanocrystalline ceria.
Abstract: Defect associates and their interactions with charge carriers, influencing the ion dynamics have been discussed for Gd3+ and Y3+ co-doped nanocrystalline ceria. Detailed Rietveld analysis of the X-Ray Diffraction data confirmed the single phase cubic fluorite structure of the compositions with the space group Fmm. An overall increase of the lattice parameter with Gd3+ ion concentration has been found. Grain and specific grain boundary conductivity have been evaluated from the complex impedance plots. A higher value dielectric constant has been observed for a co-doped sample at 20 mol% doping concentration. The interaction between dopant cations with oxygen vacancies has been found to form different defect associates and defect clusters. The association energy of co-doped samples at a 20 mol% doping concentration is observed to be a minimum in comparison with the singly doped samples of the same concentration. It has also been found that different defect clusters have a significant role on ionic conduction. The correlation among structural parameters, dielectric and conductivity responses has been discussed and established.
22 citations
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Abstract: A review of dielectric data for a wide range of solids proves the existence of a remarkable ‘universality’ of frequency and time responses which is essentially incompatible with the multiplicity of currently accepted detailed interpretations. Certain unique features of the universal behaviour strongly suggest the dominant role of many-body interactions.
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01 Jan 1979TL;DR: In this article, a brief description is given of the various manifestations of the universal fractional power law relaxation processes, which are contrasted with the classical or Debye law, and a novel very general approach based on the so-called energy criterion is introduced.
Abstract: A brief description is given of the various manifestations of the universal fractional power law relaxation processes, which are contrasted with the classical or Debye law. It is shown that the universal law is indeed found in a remarkable variety of physical and chemical situations, and this is deemed to merit a special attempt at finding a suitably general theoretical model. Several such models are briefly described, and a novel very general approach based on the so-called energy criterion is introduced. It is concluded that it is not yet possible to establish with certainty the validity of any of the models. >
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TL;DR: In this article, X-ray diffraction and Raman scattering are used to analyze the Raman spectrum of CeO2 and find that the single allowed Raman mode shifts to lower frequency with increasing doping level for all the rare earths.
Abstract: Powdered samples of the type Ce1−xRExO2−y, where RE=La, Pr, Nd, Eu, Gd, and Tb, are synthesized over the range 0≤x≤0.5 starting from nitrate solutions of the rare earths. X‐ray diffraction and Raman scattering are used to analyze the samples. These compounds, at least in the low doping regime and for strictly trivalent dopants, form solid solutions that maintain the fluorite structure of CeO2 with a change in lattice constant that is approximately proportional to the dopant ionic radius. The single allowed Raman mode, which occurs at 465 cm−1 in pure CeO2, is observed to shift to lower frequency with increasing doping level for all the rare earths. However, after correcting for the Gruneisen shift from the lattice expansion, the frequency shift is actually positive for all the strictly trivalent ions. In addition, the Raman line broadens and becomes asymmetric with a low frequency tail, and a new broad feature appears in the spectrum at ∼570 cm−1. These changes in the Raman spectrum are attributed to O va...
1,034 citations
TL;DR: In this paper, the total electrical conductivity and electron hole conductivity in solid CuCl, CuBr, and CuI between 250 and 450°C were determined with help of ac measurements on samples between copper electrodes and dc polarization measurements on the cellCu|cuprous halide|graphite.
Abstract: The total electrical conductivity and the electron hole conductivity in solid CuCl, CuBr, and CuI between 250 and 450°C have been determined with help of ac measurements on samples between copper electrodes and dc polarization measurements on the cellCu|cuprous halide|graphite.
543 citations
TL;DR: Brillouin-scattering spectra of doped Raman-active modes are measured in order to calculate the phonon-dispersion curves of ${\mathrm{CeO}}_{2}$ and the dependencies of type and concentration of defect space on dopant concentration in doped £2O are discussed.
Abstract: Polarized Raman-scattering spectra are obtained from oriented single crystals of yttria-doped ${\mathrm{CeO}}_{2}$. The temperature and dopant dependencies of Raman spectra strongly suggest that many structures in the Raman spectra of yttria-doped ${\mathrm{CeO}}_{2}$ are induced by the defect space including an ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ vacancy. The contribution to the frequency distributions of Raman-active modes from the whole Brillouin zone are estimated from the imaginary part of the simple projection of the phonon displacement-displacement Green's functions of undoped ${\mathrm{CeO}}_{2}$ crystals onto several defect spaces. The observed spectra are well explained by the linear combination of the calculated frequency distributions from the defect space consisting of the four metal ions and from that consisting of the six next-nearest-neighbor ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ ions surrounding an ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ vacancy. Brillouin-scattering spectra of ${\mathrm{CeO}}_{2}$ are also measured in order to calculate the phonon-dispersion curves of ${\mathrm{CeO}}_{2}$. The dependencies of type and concentration of defect space on dopant concentration in doped ${\mathrm{CeO}}_{2}$ are also discussed.
371 citations