Electrical transport properties of In-doped Ce1−xInxO2−δ (x = 0.1; 0.2) (original) (raw)
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Electrical Conductivity of CeO 2 Prepared from Nanosized Powders
Journal of Electroceramics, 2004
Nanosized powders of cerium dioxide with controlled physical properties were prepared by the precipitation technique using ammonium hydroxide or oxalic acid as precipitating agent. The calcined precursors were studied by nitrogen adsorption to determine the specific surface area, X-ray diffraction for phase characterization and crystallite size determination, and by laser scattering for particle size distribution. The morphology of powder particles was observed by scanning electron microscopy. It is shown that both precipitating materials may be used for the preparation of nanocrystalline powders (< 10 nm) with high values of specific surface area (> 90 m2 ⋅ g− 1). The observed differences between powders prepared from hydroxides or oxalates rely on the distribution of particle sizes and in the morphology of the agglomerated particles. Impedance spectroscopy experiments were carried out in the 5 Hz–13 MHz frequency range under controlled partial pressure of oxygen from 10 ppm to 1 atm. The analysis of these results allowed for the determination of the charge carriers responsible for the electrical transport in the ceria sintered pellets.
International Journal of Hydrogen Energy, 2011
The present work aims at the investigation of the influence of different dopants' ionic radius and concentration on the lattice parameters and the density of Ce 1Àx Ln x O 2Àd (x ¼ 0e0.20; Ln ¼ La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) solid solutions. Moreover, the temperature dependence of the linear expansion of Ce 0.8 Ln 0.2 O 2Àd ceramics is examined in the range of 300e1173 K and the respective thermal expansion coefficients are calculated. Finally, the total electrical conductivity of Ce 1Àx Ln x O 2Àd (x ¼ 0.15e0.20) and multi-component Ce (1Àx) Ln x/2 Ln' x/2 O 2Àd (x ¼ 0.20; Ln ¼ Sm, La, Gd, Dy and Ln' ¼ Dy, Nd, Er, Y) systems is studied in a wide range of temperatures in air atmosphere, as well as in a wide range of oxygen partial pressures at 1023 K and 1173 K. According to the experimental results of the present work, at the highest examined temperature of 1173 K and in air atmosphere, the maximum values of total electrical conductivity are observed in the cases of Ce 0.8 Nd 0.2 O 2Àd and Ce 0.8 Sm 0.2 O 2Àd .
Influence of microstructure on oxide ionic conductivity in doped CeO2 electrolytes
Journal of Electroceramics, 2006
Doped ceria (CeO 2) compounds are fluorite type oxides, which show oxide ionic conductivity higher than yttria stabilized zirconia, in oxidizing atmospheres. As a consequence of this, considerable interest has been shown in application of these materials for 'low (500 •-650 • C)' temperature operation of solid oxide fuel cells (SOFCs). In this study, some rare earth (eg. Gd, Sm, and Dy) doped CeO 2 nanopowders were synthesized via a carbonate co-precipitation method. Fluorite-type solid solution were able to be formed at low temperature, such as 400 • C and dense sintered bodies were subsequently fabricated in the temperature ranging from 1000 • to 1450 • C by conventional sintering (CS) method. To develop high quality solid electrolytes, the microstructure at the atomic level of these doped CeO 2 solid electrolytes were examined using transmission electron microscopy (TEM). The specimens obtained by CS had continuous and large micro-domains with a distorted pyrochlore structure or related structure, within each grain. We conclude that the conducting properties in these doped CeO 2 systems are strongly influenced by the micro-domain size in the grain. To minimize the micro-domain size, spark plasma sintering (SPS) was examined. SPS has not been used to fabricate dense sintered bodies of doped CeO 2 electrolytes, previously; carbon from the graphite dies penetrates the specimens and inhibits densification. To overcome this challenge, and to be able to produce dense sintered bodies of doped CeO 2 of a grain
Electrical and microstructural properties of Yb-doped CeO2
Journal of Asian Ceramic Societies, 2014
Nanopowdered Ce 1−x Yb x O 2−ı solid solutions (0 ≤ x ≤ 0.2) were synthesized by a self-propagating room temperature synthesis. XRD and SEM were used to study the properties of these materials as well as the Yb solubility in CeO 2 lattice. Results showed that all the obtained powders were solid solutions with a fluoritetype crystal structure and with nanometric particle size. The average size of Ce 1−x Yb x O 2−ı particles was approximately 3 nm. Electrochemical impedance spectroscopy for the sintered pellets depicted that it was possible to separate R bulk and R gb in the temperature interval of 550-800 • C. The activation energy for the bulk conduction was 1.03 eV and for grain boundary conduction was 1.14 eV. Grain boundary resistivity dominates over the other resistivities. These measurements confirmed that Yb 3+-doped CeO 2 material had a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.
Acceptor-doped BaCeO 3 perovskites have frequently been studied as high temperature proton conductors (HTPCs) where conduction occurs due to hydroxyl protons that occupy the oxide ion vacancies in the perovskite-type structure. Recently, donor-doped perovskites of the nominal composition BaCe 0.7 Zr 0.2 Nb 0.1 O 3 have demonstrated mixed proton-electron conduction in humidified H 2 and N 2. The proton conduction mechanism is assumed to be similar to that of acceptor-doped perovskites, where the reduction of B-site cations is suggested. In this study, BaCe 1À(x+y) Zr x Nb y O 3 (x ¼ 0.05-0.2, y ¼ 0.05-0.1) are characterized using X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and AC impedance spectroscopy. The role of composition and sintering temperature on microstructural, chemical, stoichiometric, and electrical properties is thoroughly investigated. PXRD shows the formation of orthorhombic perovskites in all samples and SEM images reveal that a decrease in porosity and increase in grain size are significantly affected by relative Zr and Nb dopant levels. The improved densification caused by the Nb doping leads to enhanced total conductivity by lowering the grain-boundary resistance. Surface analysis by XPS indicates that Ba vacancies in as-prepared BaCe 1À(x+y) Zr x Nb y O 3 can be controlled by composition and temperature control. The co-doping of Nb and Zr lead to enhanced chemical stability in CO 2 at elevated temperatures compared to the parent compound. The bulk electrical conductivity decreases with increasing Zr content in BaCe 1À(x+y) Zr x Nb y O 3 in air. Among the samples investigated in this work, BaCe 0.9 Zr 0.05 Nb 0.05 O 3 exhibits the highest bulk conductivity of 10 À3 S cm À1 at 400 C with an activation energy of 0.43 eV (400-700 C).
Inorganic Chemistry, 2008
Fast oxide ion conducting Ce 1-x M x O 2-δ (M) In, Sm; x) 0.1, 0.2) and Ce 0.8 Sm 0.05 Ca 0.15 O 1.825 were prepared from the corresponding perovskite-like structured materials with nominal chemical composition of BaCe 1-x M x O 3-δ and BaCe 0.8 Sm 0.05 Ca 0.15 O 2.825 , respectively, by reacting with CO 2 at 800°C for 12 h. Powder X-ray diffraction (PXRD) analysis showed the formation of fluorite-type CeO 2 and BaCO 3 just after reaction with CO 2. The amount of CO 2 gained per ceramic gram was found to be consistent with the Ba content. The CO 2 reacted samples were washed with dilute HCl and water, and the resultant solid product was characterized structurally and electrically employing various solid-state characterization methods, including PXRD, and alternating current (ac) impedance spectroscopy. The lattice constant of presently prepared Ce 1-x M x O 2-δ and Ce 0.8 Sm 0.05 Ca 0. 15 O 1.825 by a CO 2 capture technique follows the expected ionic radii trend. For example, In-doped Ce 0.9 In 0.1 O 1.95 (In 3+ (VIII)) 0.92 Å) sample showed a fluorite-type cell constant of 5.398(1) Å, which is lower than the parent CeO 2 (5.411 Å, Ce 4+ (VIII)) 0.97 Å). Our attempt to prepare single-phase In-doped CeO 2 samples at 800, 1000, and 1500°C using the ceramic method was unsuccessful. However, we were able to prepare single-phase Ce 0.9 In 0.1 O 1.95 and Ce 0.8 In 0.2 O 1.9 by the CO 2 capture method from the corresponding barium perovskites. The PXRD studies showed that the In-doped samples are thermodynamically unstable above 800°C. The ac electrical conductivity studies using Pt electrodes showed the presence of bulk, grain-boundary, and electrode contributions over the investigated temperature range in the frequency range of 10-2-10 7 Hz. The bulk ionic conductivity and activation energy for the electrical conductivity of presently prepared Sm-and (Sm + Ca)-doped CeO 2 samples shows conductivities similar to those of materials prepared by the ceramic method reported in the literature. For instance, the conductivity of Ce 0.8 Sm 0.2 O 1.9 using the CO 2 capture technique was determined to be 4.1 × 10-3 S/cm, and the conductivity of the same sample prepared using the ceramic method was 3.9 × 10-3 S/cm at 500°C. The apparent activation energy of the area-specific polarization resistance for the symmetric cell (Sm,Sr)CoO 3-x |Ce 0.8 Sm 0.2 O 1.9 |(Sm,Sr)CoO 3-x was determined to be 1 eV in air.
Na2O doped CeO2 and their structural, optical, conducting and dielectric properties
Physica B-condensed Matter, 2018
In the present study, Na 2 O doped CeO 2 has been prepared by solid state reaction method. The prepared samples are characterized by X-ray diffraction (XRD), UV-Visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscope (SEM) and Impedance spectroscopy. The optical band gap of all the samples lies in the semiconducting range i.e. 3.04-3.25 eV. The highest optical band gap is observed for 5 mol% Na 2 O doped CeO 2. The SEM images show a non-uniform distribution of particles with an average particle size of ~ 3.15 μm for all the samples. The lowest dielectric constant is observed to be ~11 at 100 °C and 100 Hz for 10 mol% doped CeO 2 which is lower than the undoped CeO 2. The conductivity of the samples lies in the range of 10-7 S/cm at 700 °C.
Design of high quality doped CeO2 solid electrolytes with nanohetero structure
Doped ceria (CeO 2) compounds are fluorite related oxides which show oxide ionic conductivity higher than yttria-stabilized zirconia in oxidizing atmosphere. As a consequence of this, a considerable interest has been shown in application of these materials for low (400−650°C) temperature operation of solid oxide fuel cells (SOFCs). In this paper, our experimental data about the influence of microstructure at the atomic level on electrochemical properties were reviewed in order to develop high quality doped CeO 2 electrolytes in fuel cell applications. Using this data in the present paper, our original idea for a design of nanodomain structure in doped CeO 2 electrolytes was suggested. The nanosized powders and dense sintered bodies of M doped CeO 2 (M:Sm,Gd,La,Y,Yb, and Dy) compounds were fabricated. Also nanostructural features in these specimens were introduced for conclusion of relationship between electrolytic properties and domain structure in doped CeO 2. It is essential that the electrolytic properties in doped CeO 2 solid electrolytes reflect in changes of microstructure even down to the atomic scale. Accordingly, a combined approach of nanostructure fabrication, electrical measurement and structure characterization was required to develop superior quality doped CeO 2 electrolytes in the fuel cells. Key words doped CeO 2 • oxide ionic conductivity • microdomain • low temperature operation of fuel cells application • nanohetero structure • domain structure
Solid State Ionics, 2020
We have measured water uptake and hydration enthalpy in 50% La and Nd doped CeO 2 , also to be taken as compositions in the series La 2−x Nd x Ce 2 O 7 (x = 0.0, 0.5, 1.0 and 2.0) using combined thermogravimetry (TG) and differential scanning calorimetry (DSC), TG-DSC. The TG-DSC data unambiguously yield standard molar hydration enthalpies of~−74 kJ/mol independent of water uptake. The interpretation of the TG results, however, does not fit a classical model of hydration of all oxygen vacancies. Instead, the hydration appears to be limited to a small fraction of the free vacancies. Hydration further decreases as the Nd content (x) and long-range order increases and regions of disorder decrease. We propose a new model explaining why hydration occurs only in a small fraction of the nominally free vacancies: The higher basicity of La/Nd compared to Ce promotes protonation at oxide ion sites with high coordination to La/Nd, and the observed water uptake and modelling suggests that mainly oxide ions fully coordinated to 4 La/Nd neighbours become protonated. The statistical variation of coordination around oxygen sites in a disordered fluorite oxide creates a limited number of such oxide ions sites which results in limited hydration. The model matches well the experimental results and DFT calculations of proton trapping at the fully La-coordinated sites for 50% La-doped CeO 2 , and also rationalizes conductivity data.
Oxygen vacancy ordering and the conductivity maximum in Y2O3-doped CeO2
The defect structure and ionic diffusion processes within the anion-deficient, fluorite structured system Ce1−xYxO2−x/2 have been investigated at high temperatures (873 K – 1073 K) as a function of dopant concentration, x, using a combination of neutron diffraction studies, impedance spectroscopy measurements of the ionic conductivity and molecular dynamics (MD) simulations using interionic potentials developed from ab initio calculations. Particular attention is paid to the short-range ion-ion correlations, with no strong evidence that the anion vacancies prefer, at high temperature, to reside in the vicinity of either cationic species. However, the vacancy-vacancy interactions play a more important role, with preferential ordering of vacancy pairs along the 111 directions, driven by their strong repulsion at closer distances, becoming dominant at high values of x. This effect explains the presence of a maximum in the ionic conductivity in the intermediate temperature range (873 K – 1073 K) as a function of increasing x. The wider implications of these conclusions for understanding the structure-property relationships within anion-deficient fluorite structured oxides are briefly discussed, with reference to complementary studies of yttria and/or scandiaium doped zirconia Zr1−xYxO2−x/2 and Zr1−xScxO2−x/2 published previously.