Peculiarities of ionic transport of oxygen vacancy conducting superionic ceramics (original) (raw)
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XPS and impedance spectroscopy of some oxygen vacancy conducting solid electrolyte ceramics
Solid State Ionics, 2011
The powder of 10GDC, 15SDC, and 8YSZ compounds with different surface areas (S BET ) was used for the sintering of the ceramics. The sintering of the ceramic samples was conducted in air at 1773 K. The surfaces of the ceramics were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The complex impedance and electric conductivity in frequency range (10-3⋅10 9 ) Hz and temperature range from 300 to 700 K were carried out. Relaxation dispersions of the electrical parameters were found for all compounds. The dispersions are caused by the oxygen vacancy (V O •• )transport in grain boundaries and bulk of the ceramic samples. The values of the bulk and total conductivities of the samples depend on the S BET of the powder used for sintering of the ceramics.
Sintering of oxygen ion conductive ceramics and their electrical properties
Lithuanian Journal of Physics, 2012
Oxygen ion conducting ceramics (Sc 2 O 3) 0.1 (ZrO 2) 0.9 , (Sc 2 O 3) 0.1 (CeO 2) 0.01 (ZrO 2) 0.89 and Ce 0.9 Gd 0.1 O 1.95 were sintered from powders with different specific surface areas. The produced ceramics were studied by scanning electron microscopy and impedance spectroscopy methods. Impedance spectroscopy measurements were performed in a wide frequency range of 10 Hz-3 GHz at temperatures up to 900 K in air. Temperature dependences of bulk and total ionic conductivities of ceramics were investigated. High bulk ionic conductivity of the order of 1 S/m at 900 K for 10ScSZ and 10Sc1CeSZ ceramics was achieved. Total ionic conductivity for both types of 10GDC ceramics was of the order of 0.1 S/m at 700 K.
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.
XPS and impedance spectroscopy of Gd doped CeO 2 superionic ceramics
Lithuanian Journal of Physics, 2009
Ce0.9Gd0.1O1.95 (CGO-10) and Ce0.8Gd0.2O1.9 (CGO-20) ceramics have been sintered by using commercial powders of Fuel Cell Materials company. The powders of different surface area (BET [m 2 /g]) were used to prepare the ceramics. Elemental compositions of CGO solid electrolytes' surfaces have been investigated in 10 −7 Pa vacuum by X-ray photoelectron spectroscopy and the ratio Ce 4+ /Ce 3+ has been estimated. Electrical parameters of CGO ceramics were investigated in the frequency range from 1 MHz to 1.2 GHz. Temperature-dependant bulk ionic conductivity (σ b) was found to follow the Arrhenius law. Ionic conductivity of CGO-10 was higher compared to that of CGO-20. The bulk ionic conductivity of CGO-10 ceramics slightly depended on the grain size of initial powder.
Electrical properties of ceria-based oxides and their application to solid oxide fuel cells
Solid State Ionics, 1992
Ionic conductivities of ceria-alkaline-earth and -rare-earth oxide systems were investigated in relation to their structures, electrical conductivities, and reducibilities. Samaria and gadolinia-doped ceria samples exhibited the highest electrical conductivity in ceria-based oxides because of the close ionic radii of Sm 3 + and Gd 3 + to that of Ce 4+. The ionic conductivity of samariadoped ceria was also measured by an ac four-probe method with electron blocking electrodes. A solid oxide fuel cell with a samaria-doped ceria electrolyte produced high electric power, because of its highest oxygen ionic conductivity. The reduction of ceria electrolyte at the fuel side could be suppressed by a coating of stabilized zirconia thin film on the ceria surface. The anodic overvoltage of the doped ceria/anode interface was very small,
Research Journal of Chemistry and Environment, 2021
The search for new cost-effective electrolyte materials for IT-SOFC towards its mass scale commercialization has gained momentum in recent years. The Ca-doped ceria having composition Ce0.91Ca0.09O2 was prepared using the facile conventional solid-state method. The structural and electrical properties of low sintered ceramic samples have been characterized by X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy (DRS) and A.C. impedance technique respectively. The oxide ion conductivity was measured between the temperatures 573 K−973 K in air. The obtained results showed that total conductivity is mainly dependent on the grain boundary effect. The nanocrystalline Ce0.91Ca0.09O2 exhibited the high total ionic conductivity of 7.36 10 3 S cm 1 at 973 K with a lower activation energy of 0.96 eV. The obtained results highlight the use of cost-effective dopant in ceria lattice to develop commercially viable electrolyte materials for IT-SOFC.
Electronic transport in Ce0.8Sm0.2O1.9−δ ceramics under reducing conditions
Electrochimica Acta, 2003
Ce 0.8 Sm 0.2 O 1.9(d powders were prepared by a freeze drying method and used to obtain ceramic disks. These samples were used to study the electronic transport properties of this material. A Hebb Á/Wagner method was used to obtain the electronic conductivity under ion blocking conditions. Typical values of electronic conductivity measured for this material at 800 8C were about 0.37 S m (1 at Po 2 0/10 (16 atm and 0.58 S m (1 at P O 2 0/10 (18 atm. These values are significantly lower than results reported for ceria-based materials with different trivalent additives. A coulometric titration method was used to estimate the charge carrier concentrations, and the mobility of carriers was obtained on combining the results of conductivity and concentration. Typical values of mobility show weak temperature dependence and decrease with increasing oxygen deficiency, suggesting a limiting value of about 0.5)/10 (7 m 2. V (1 s (1 for relatively high d .
Journal of Power Sources, 2004
Twenty percentage of Gd 2 O 3-doped ceria solid solution has been prepared as an electrolyte for solid oxide fuel cells via the conventional mixed-oxide method from high-purity commercial CeO 2 and Gd 2 O 3. The solubility of Gd 2 O 3 in CeO 2 in the temperature range of 1300-1700 • C has been examined based on the measurements of the lattice parameter. It is found that the dissolution of Gd 2 O 3 in CeO 2 is completed at 1600 • C for 5 h. The addition of Gd 2 O 3 increases sintering temperature, retards densification, and also depresses grain growth as compared with undoped CeO 2. The sample sintered at 1550 • C for 5 h has the highest grain boundary conductivity, while the highest grain interior conductivity is achieved for the sample sintered at 1600 • C for 5 h. It is also observed that below 500 • C, the maximum total conductivity is exhibited by the former sample, but above 500 • C, for the latter one.
Journal of Alloys and Compounds, 2013
Attempts have been made to synthesize a few compositions in the system Ce 0.90 Mg 0.10Àx Sr x O 1.90 (x = 0.00, 0.02, 0.04 and 0.06) by citrate-nitrate auto-combustion method. XRD patterns reveal that all the samples have fluorite crystal structure similar to ceria. Microstructures of samples have been studied by scanning electron microscope. Ionic conductivity of singly doped and co-doped ceria has been investigated as a function of temperature by AC impedance spectroscopy in the temperature range 200-700°C. Impedance plots show a significant decrease in grain boundary resistance after partial substitution of Sr in Mg-doped ceria in the intermediate temperature range. Composition with x = 0.04 shows the highest ionic conductivity (2.0 Â 10 À2 S/cm at 700°C) among all the samples studied. Ó 2013 Elsevier B.V. All rights reserved. 2 (x = 0.30) system which was synthesized by glycine-nitrate process and they found single phase formation in this system and the grain growth of sintered samples was observed to hindered with an increase in Gd content. Composition Ce 0.90 Gd 0.10 O 1.95 was synthesized using combustion technique by Jadhav et al. [14] and they found that the relative density of the sample was more than 90% at 1200°C which was also confirmed by SEM analysis. The grain and grain boundary conductivity of a GDC (Ce 0.90 Gd 0.10 O 1.95
P-type electronic transport in Ce0.8Gd0.2O2-δ: The effect of transition metal oxide sintering aids
Journal of Electroceramics, 2002
Small (2 mol%) additions of cobalt, iron and copper oxides into Ce 0.8 Gd 0.2 O 2−δ considerably improve sinterability of ceria-gadolinia (CGO) solid electrolyte, making it possible to obtain ceramics with 95-99% density and sub-micron grain sizes at 1170-1370 K. The minor dopant additions have no essential effect on the total and ionic conductivity, whilst the p-type conduction in the transition metal-containing materials at 900-1200 K is 8-30 times higher than that in pure CGO. The oxygen ion transference numbers of the Co-, Fe-and Cu-doped ceramics, determined by the modified e.m.f. technique under oxygen/air gradient, are in the range 0.89-0.99. The electron-hole contribution to the total conductivity increases with temperature, as the activation energy for ionic conduction, 78 to 82 kJ/mol, is significantly lower than that for the p-type electronic transport (139-146 kJ/mol). The results show that CGO sintered with such additions can still be used as solid electrolytes for intermediatetemperature electrochemical applications, including solid oxide fuel cells (SOFCs) operating at 770-970 K, but that increasing operation temperature is undesirable due to performance loss.