Molecular dynamics simulations of the deformation behavior of gadolinia-doped ceria solid electrolytes under tensile loading (original) (raw)
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Effect of strain on the oxygen diffusion in yttria and gadolinia co-doped ceria
Solid State Ionics, 2013
Atomic scale simulations have been used to investigate the impact of co-doping (yttrium and gadolinium) and strain on oxygen diffusion and binding of dopant-vacancy clusters in ceria. Doped ceria in its relaxed or strained form is used as an electrolyte for solid oxide fuel cell applications. For unstrained co-doped ceria we calculate an activation energy for migration of 0.70-0.75 eV in the temperature range of 973-1873 K. Co-doping with yttrium and gadolinium only affected oxide ion diffusion to a small degree when compared to single doping. The diffusion coefficient was substantially increased by tensile strain while compressive strain caused a decrease. To gain further insight why tensile strain leads to higher diffusivity static simulations were employed. It is calculated that tensile strain reduces the binding energies of clusters between oxygen vacancies and trivalent dopant atoms while compressive strain leads to higher binding energies.
Journal of Electroceramics, 2005
In this study, we report key functional properties of gadolinium-doped ceria (Gd 0.1 Ce 0.9 O 1.95 , GDC) sintered at low temperatures as well as single-cell electrochemical performance of a single-cell prepared there of. GDC solid solutions were sintered at various temperatures ranging 1100-1400 • C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density measurements, mechanical strength tests and electrical conductivity measurements. The dry-pressed GDC disc sample sintered at 1100 • C was found to have 96% of the theoretical density and higher sintering temperatures led to higher densities. SEM micrographs of the fracture and plan surfaces of the sintered discs established the absence of any open pores. The sample sintered at 1100 • C exhibited high electrical conductivity of 0.027 S/cm at 650 • C. The mechanical strength of the sintered samples was determined to be in the range of 150-175 MPa. Greater than 96% of theoretical density, good mechanical strength, and high electrical conductivity of GDC disc samples sintered at 1100 • C established the viability of low-temperature processing of GDC for its use as an SOFC electrolyte. Accordingly, a single-cell was prepared by co-sintering of GDC electrolyte and LSCF-GDC cathode at 1100 • C and subsequent firing of CuO-GDC anode at 900 • C. The electrochemical performance of the cell was evaluated in H 2 fuel at 650 • C.
Investigation of the stability of ceria-gadolinia electrolytes in solid oxide fuel cell environments
Solid State Ionics, 1999
Doped ceria-based materials are potential electrolytes for use in lower operating temperature (500-700 o C) solid oxide fuel cells because of their high ionic conductivity. In this study, impedance behaviour and microstructure of the (Ce 0.8 Gd 0.2)O 1.9 exposed to mild fuel environments (H 2-N 2 mixtures) have been investigated. The exposure of specimens to H 2-N 2 mixtures at 1000 o C resulted in a substantial expansion of the lattice as a consequence of the reduction of Ce 4+ to Ce 3+ , which in turn led to the development of microcracks and loss of continuity at the grain boundary region and increase in both the grain boundary (major effect) and the lattice (minor effect) resistivity. The behaviour for the grain boundary resistivity after the 800 o C exposure was somewhat similar although expansion of the lattice at 800 o C (or lower temperatures) was considerably less conspicuous. After exposure to H 2-N 2 atmosphere at lower temperatures (650 and 500 o C), although no significant increase in the grain boundary resistivity for exposures up to 1000 hours was observed, the shape of the grain boundary arc was clearly affected. The large increase in the grain boundary resistivity in reduced specimens has been attributed to the observed microcracking, loss of continuity between grains and possibly the formation of new phase regions with extremely poor oxygen-ion conductivity along grain boundaries during the reduction. The disruption to the microstructure is not recovered on subsequent oxidation in air.
Correlation between atomic positional shift, oxygen vacancy defects, and oxide ion conductivity in doped ceria system has been established in the gadolinium doped ceria system from X-ray diffraction (XRD) and Raman spectroscopy study at operating temperature (300-600 C) of Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC). High temperature XRD data are used to quantify atomic positional shift from mean position with temperature. The Raman spectroscopy study shows additional vibration modes related to ordering of defect spaces ðGd 0
Materials Letters, 2020
In light of the recent discovery of giant electrostriction in defective fluorites, here we investigate the interplay between mechanical, electrochemical and electromechanical properties of oxygen defective ceria compositions (Ce1−xGdxO2−δ) as the effect of Gd-doping (x = 0.05−0.3) at low temperatures. Highly dense polycrystalline ceramics are prepared as micron-size grains with a minimized grain boundary extent. Electrochemical ionic migration reveals that doping controls the configuration of oxygen vacancies in the samples. Unexpectedly, we observe that electromechanical activity is depends on oxygen vacancy configuration rather than on its nominal concentration. The primary creep at room temperature indicates a declining viscoelastic trend with increasing oxygen defects.
Ion transport mechanism in ceria based system is understood by correlating atomic positional shift, oxygen vacancy defects with oxide ion conductivity in doped ceria system. X-ray diffraction (XRD) and Raman spectroscopy study at operating temperature (300-600 o C) of Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) are performed. High temperature XRD data is used to quantify atomic positional shifting from mean position with temperature. The Raman spectroscopy study shows additional vibration modes related to ordering of defect species * ' ) ( • • − o Ce V M and x o Ce V M ) 2 ( ' • • − generated due to association of extrinsic oxygen vacancies and dopant M 2+ / 3+ , which disappear at 450 o C; indicating oxygen vacancies dissociation from the defect complex. The experimental evidences of cation-anion positional shifting and oxygen vacancies dissociation from defect complex in the IT-SOFC operating temperature are discussed to correlate with activation energy for ionic conductivity.
Acta Materialia, 2019
Some oxygen defective metal oxides, such as cerium and bismuth oxides, have recently shown exceptional electrostrictive properties that are even superior to the best performing lead-based electrostrictors, e.g. lead-magnesium-niobates (PMN). Compared to piezoelectric ceramics, electromechanical mechanisms of such materials do not depend on crystalline symmetry, but on the concentration of oxygen vacancy (V O ••) in the lattice. In this work, we investigate for the first time the role of oxygen defect configuration on the electro-chemomechanical properties. This is achieved by tuning the oxygen defects blocking barrier density in polycrystalline gadolinium doped ceria with known oxygen vacancy concentration, Ce0.9Gd0.1O2-δ, δ = 0.05. Nanometric starting powders of ca. 12 nm are sintered in different conditions, including field assisted spark plasma sintering (SPS), fast firing and conventional method at high temperatures. These approaches allow controlling grain size and Gd-dopant diffusion, i.e. via thermally driven solute drag mechanism. By correlating the electro-chemomechanical properties, we show that oxygen vacancy distribution in the materials play a key role in ceria electrostriction, overcoming the expected contributions from grain size and dopant concentration.
Ceramics International, 2020
The gadolinium-doped ceria is investigated as electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its oxide ion conductivity. The doping of Gd 3+ to Ce 4+ can introduce a small strain in the lattice thereby improved conductivity with low activation energy is expected. The 20 mol. % gadolinium doped ceria (Ce 0.8 Gd 0.2 O 2− δ) nanocrystalline powder is prepared here by citrate-complexation method. The XRD, Rietveld refinement, FTIR, UV-Visible, FESEM/EDX, and a c-impedance techniques are used to characterize this sample. The oxide ion conductivity is determined between 523 − 1023 K. The Ce 0.8 Gd 0.2 O 2− δ shows highest oxide ion conductivity of 6.79 × 10 − 3 S cm − 1 and 1.11 × 10 − 2 S cm − 1 at 973 K and 1023 K, respectively. The Ce 0.8 Gd 0.2 O 2− δ showed lower activation energies of 1.09, 0.70, and 0.88 eV for grain, grain boundary, and total conduction, respectively. Thus, the nano crystalline Ce 0.8 Gd 0.2 O 2− δ is proposed as potential electrolyte for IT-SOFCs.
Electrolyte materials for solid oxide fuel cells derived from metal complexes: Gadolinia-doped ceria
Ceramics International, 2012
Gadolinia doped ceria (GDC) powders with different gadolinium contents were successfully prepared by the thermal decomposition of ceria complexes. All the calcined powder samples were found to be ceria-based solid-solutions having a fluorite-type structure. The powders were coldisostatically pressed and sintered in air at 1500 8C for 5 h to attain a sintered density of about 90% of its theoretical value. The electrical conductivity of the GDC pellets in air was studied as a function of temperature in the 225-700 8C range, by using two-probe electrochemical impedance spectroscopy measurements. The highest total conductivity (s 600 8C = 0.025 S/cm) was found for the Ce 0.85 Gd 0.15 O 1.925 composition.
Effect of co-dopant addition on properties of gadolinia-doped ceria electrolyte
Journal of power sources, 2000
. Various trivalent oxides were added as co-dopants to gadolinia-doped ceria GDC electrolyte used for solid oxide fuel cells at up to 5 mol%. An examination was made on how they affect the electrical conductivity of the electrolyte and, eventually, the open-circuit voltage Ž . Ž . OCV of a unit cell. Through a comparison of the thermal expansion coefficients TEC , it was investigated whether or not the co-doped electrolytes are thermomechanically compatible with other cell components. The addition of co-dopants generally improve the electrical Ž . properties of the electrolyte by yielding greater OCV values and not changing the TEC significantly 5% at most , except in the case of Ž . Pr. Among the electrolytes examined, the one co-doped with Sm 3 mol% shows the best improvement in performance. q 2000 Elsevier Science S.A. All rights reserved.