Effect of Reduced Atmosphere Sintering on Blocking Grain Boundaries in Rare-Earth Doped Ceria

Rare-earth doped ceria materials are amongst the top choices for use in electrolytes and composite electrodes in intermediate temperature solid oxide fuel cells. Trivalent acceptor dopants such as gadolinium, which mediate the ionic conductivity in ceria by creating oxygen vacancies, have a tendency to segregate at grain boundaries and triple points. This leads to formation of ionically resistive blocking grain boundaries and necessitates high operating temperatures to overcome this barrier. In an effort to improve the grain boundary conductivity, we studied the effect of a modified sintering cycle, where 10 mol% gadolinia doped ceria was sintered under a reducing atmosphere and subsequently reoxidized. A detailed analysis of the complex impedance, conductivity, and activation energy values was performed. The analysis shows that for samples processed thus, the ionic conductivity improves when compared with conventionally processed samples sintered in air. Equivalent circuit fitting shows that this improvement in conductivity is mainly due to a drop in the grain boundary resistance. Based on comparison of activation energy values for the conventionally processed vs. reduced-reoxidized samples, this drop can be attributed to a diminished blocking effect of defect-associates at the grain boundaries

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High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes

Coatings ◽

10.3390/coatings11060724 ◽

2021 ◽

Vol 11 (6) ◽

pp. 724

Author(s):

Sara Massardo ◽

Alessandro Cingolani ◽

Cristina Artini

Keyword(s):

Thin Films ◽

High Pressure ◽

Rare Earth ◽

Ionic Conductivity ◽

Bulk Material ◽

Threshold Temperature ◽

Doped Ceria ◽

X Ray Diffraction ◽

X Ray ◽

Rare Earth Doped

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through the mobility of oxygen ions above a certain threshold temperature. This feature is in turn limited by the association of defects, which hinders the movement of ions through the lattice. In addition to these issues, ionic conductivity in thin films is dominated by the presence of the film/substrate interface, where a strain can arise as a consequence of lattice mismatch. A tensile strain, in particular, when not released through the occurrence of dislocations, enhances ionic conduction through the reduction of activation energy. Within this complex framework, high pressure X-ray diffraction investigations performed on the bulk material are of great help in estimating the bulk modulus of the material, and hence its compressibility, namely its tolerance toward the application of a compressive/tensile stress. In this review, an overview is given about the correlation between structure and transport properties in rare earth-doped ceria films, and the role of high pressure X-ray diffraction studies in the selection of the most proper compositions for the design of thin films.

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Effect of Doping Concentration on Grain Boundary Conductivity of Samaria Doped Ceria Composites

Journal of The Electrochemical Society ◽

10.1149/1945-7111/ac4371 ◽

2021 ◽

Author(s):

Prerna Vinchhi ◽

Roma Patel ◽

Indrajit Mukhopadhyay ◽

Abhijit Ray ◽

Ranjan Pati

Keyword(s):

Ionic Conductivity ◽

Grain Boundary ◽

Doping Concentration ◽

Single Phase ◽

Precipitation Method ◽

Molecular Water ◽

Doped Ceria ◽

Boundary Conductivity ◽

Co Precipitation ◽

Hydrated Oxide

Abstract This work aims to study the effect of Sm3+ doping concentration on the grain boundary ionic conductivity of ceria. The materials were prepared by a modified co-precipitation method, where molecular water associated with the precursor has been utilized to facilitate the hydroxylation process. The synthesized hydroxide / hydrated oxide materials were calcined and the green body (pellet) has been sintered at high temperature in order to achieve highly dense (~ 96 %) pellet. The structural analyses were done using XRD and Raman spectroscopy, which confirm the single phase cubic structure of samaria doped ceria (SDC) nanoparticles and the surface morphology of sintered samples was studied using FESEM. The ionic conductivity was measured by AC impedance spectroscopy of the sintered pellets in the temperature range of 400-700 °C, which shows superior grain boundary conductivity. The grain boundary ionic conductivity of around 0.111 S/cm has been obtained for 15SDC composition at 600 °C.

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Impedance Spectroscopy Analysis of p Type Li Doped ZnO Thin Film Effect

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.415-417.1925 ◽

2011 ◽

Vol 415-417 ◽

pp. 1925-1932 ◽

Cited By ~ 2

Author(s):

Kuo Chuang Chiu ◽

Yu Han Wu

Keyword(s):

Thin Film ◽

Impedance Spectroscopy ◽

Grain Boundary ◽

Grain Boundaries ◽

Complex Impedance ◽

Spectroscopy Analysis ◽

Boundary Conductivity ◽

Impedance Spectroscopy Technique ◽

P Type ◽

Li Content

Impedance spectroscopy technique was employed to characterize the LixZn1-xO2 (x=0.001~0.008) polycrystalline thin film. IS is shown to be an efficient method capable of detecting the contributions of the resistances of grains and grain boundaries resistance to the complex impedance of a compound, accurately estimating its electrical conductivity as well as its corresponding activation energies and conclude on its structural properties. This is demonstrated for the case of lithium segregation in the grain/grain boundary of LixZn1-xO2., we found that the activation energy decrease associated with grain-boundary conductivity reflects the onset of the segregation of excessive Li in the grain boundaries when the Li-content exceeds 0.5 mol%. For Li-content below 0.5mol% is the detection of a transition from p-type conductivity. It might be due to that the Li+ doped mainly in grains and no precipitation observed on the grain boundaries. So we could be process stable p type thin film for Li content below 0.5mol%.

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Increased ionic conductivity in microwave hydrothermally synthesized rare-earth doped ceria Ce1−xRExO2−(x/2)

Journal of Power Sources ◽

10.1016/j.jpowsour.2012.02.082 ◽

2012 ◽

Vol 209 ◽

pp. 163-171 ◽

Cited By ~ 46

Author(s):

Jesús Prado-Gonjal ◽

Rainer Schmidt ◽

Jesús Espíndola-Canuto ◽

P. Ramos-Alvarez ◽

Emilio Morán

Keyword(s):

Rare Earth ◽

Ionic Conductivity ◽

Doped Ceria ◽

Rare Earth Doped

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Influence of Lithium Content on the Structure and Ionic Conductivity of Perovskite $\mbox{La}_{(2/3) - x}\mbox{Li}_{3x}\mbox{TiO}_{3}$ Made by Double Mechanical Alloying Method

Communications in Physics ◽

10.15625/0868-3166/24/3s1/5074 ◽

2014 ◽

Vol 24 (3S1) ◽

pp. 33-39

Author(s):

Le Dinh Trong

Keyword(s):

Activation Energy ◽

Ionic Conductivity ◽

Grain Boundary ◽

Mechanical Alloying ◽

Room Temperature ◽

Lithium Content ◽

Boundary Conductivity ◽

Structural Modifications ◽

Li Ion ◽

Conductive Properties

Perovskite La$_{(2/3) - x}$Li$_{3x}$TiO$_{3}$ samples with 0.06 $ \leq x \leq 0.15$ were prepared by a double mechanical alloying method. Structure and Li$^{ + }$-ion conductive properties of the La$_{(2 / 3) - x}$Li$_{3x}$TiO$_{3}$ samples were investigated. Most of the analyzed perovskite samples exhibit a double unit cell. In these samples, a change of symmetry from tetragonal to orthorhombic is observed for sample with lithium content x = 0.06. Structural modifications were obtained mainly due to the cation vacancies ordering along the c-axis, which disappeared gradually when the lithium content increased. At room temperature, the maximum values of grains and grain boundaries conductivities of the La$_{(2 / 3) - x}$Li$_{3x}$TiO$_{3}$ samples were found to be of $1.5\times 10$^{ - 3}$ S/cm and $5.8 \times 10^{ - 5}$ S/cm, respectively. The temperature dependence of ionic conductivity obeyed a non-Arrhenius behaviour. At temperature from 30 to 125$^{\circ}$C, the activation energy for grain and grain-boundary conductivity was found to be of $\sim $ 0.23 eV and $\sim $ 0.32 eV, respectively.

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FREQUENCY DEPENDENCE OF THE GRAIN-BOUNDARY CONDUCTIVITY IN (Y2O3, CaO)-STABILIZED ZrO2

International Journal of Modern Physics B ◽

10.1142/s0217979211057827 ◽

2011 ◽

Vol 25 (01) ◽

pp. 131-142 ◽

Cited By ~ 3

Author(s):

TONGWEI LI ◽

WEIWEI JU ◽

JINCANG ZHANG

Keyword(s):

Activation Energy ◽

Grain Boundary ◽

Frequency Dependence ◽

Power Law ◽

Boundary Effect ◽

Complex Impedance ◽

Impedance Method ◽

Boundary Conductivity ◽

Grain Boundary Effect ◽

Power Law Parameters

Five samples of mixed Y 2 O 3/ CaO doped ZrO 2 electrolytes, with the same nominal chemical composition of ( ZrO 2)0.90–( Y 2 O 3)0.04-( CaO )0.06, were sintered at 1600°C for 2, 4, 6, 8 and 10 h, respectively. The frequency dependence of the grain-boundary conductivity of each sample was measured using complex impedance method in the temperature range from 773 to 1073 K and experimental results were analyzed according to a power law, which was frequently referred to as the so-called universal dynamic response (UDR). Results indicated the apparent ac grain-boundary conductivity can be well-described by the power law and some useful information about the grain-boundary effect, such as the activation energy of the grain-boundary conduction and the dissociated energy of the charge carrier in the space charge layer, can be obtained by analyzing the temperature dependence of the power law parameters.

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