Linking Macroscopic and Nanoscopic Ionic Conductivity: A Semiempirical Framework for Characterizing Grain Boundary Conductivity in Polycrystalline Ceramics

Perovskite La0.67-xLi3xTiO3 with x = 0.10, 0.11, 0.12 and 0.13 were firstly annealed at 800 oC then treated by reactive milling, followed by post-annealing at temperatures from 1100 to 1200oC. The crystalline structure of grain and grain-boundary were characterized by XRD and SEM. The impedance measurements showed that nanocrystalline La0.67-xLi3xTiO3 after being annealed at 1150 oC possessed a grain conductivity as high as 1.3×10-3 S.cm-1. The grain-boundary conductivity was enhanced one order in magnitude after annealing at temperature higher 1100oC and consists of 5.8×10-5 S.cm-1. The results have also showed the limitation of the adiabatic thermal treatment for the improvement of the grain-boundary conductivity and suggested the way to overcome the limitation by rapidly cooling the samples from the high temperature to room temperature.

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

Inorganics ◽

10.3390/inorganics9080063 ◽

2021 ◽

Vol 9 (8) ◽

pp. 63

Author(s):

Soumitra Sulekar ◽

Mehrad Mehr ◽

Ji Hyun Kim ◽

Juan Claudio Nino

Keyword(s):

Activation Energy ◽

Rare Earth ◽

Ionic Conductivity ◽

Grain Boundary ◽

Grain Boundaries ◽

Complex Impedance ◽

Doped Ceria ◽

Composite Electrodes ◽

Boundary Conductivity ◽

Rare Earth Doped

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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