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Lithium ionic conduction and relaxation dynamics of spark plasma sintered Li5La3Ta2O12 garnet nanoceramics.

Ahmad MM - Nanoscale Res Lett (2015)

Bottom Line: The grain size of the SPS nanoceramics is in the 50 to 100 nm range, indicating minimal grain growth during the SPS experiments.Interestingly, we found that only a small fraction of lithium ions of 3.9% out of the total lithium content are mobile and contribute to the conduction process.Moreover, the relaxation dynamics in the investigated materials have been studied through the electric modulus formalism.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, College of Science, King Faisal University, Hofuf, Al-Ahsaa, 31982 Saudi Arabia ; Physics Department, Faculty of Science, Assiut University in The New Valley, El-Kharga, The New Valley, 72511 Egypt.

ABSTRACT
In the present work, nanoceramics of Li5La3Ta2O12 (LLT) lithium ion conductors with the garnet-like structure are fabricated by spark plasma sintering (SPS) technique at different temperatures of 850°C, 875°C, and 900°C (SPS-850, SPS-875, and SPS-900). The grain size of the SPS nanoceramics is in the 50 to 100 nm range, indicating minimal grain growth during the SPS experiments. The ionic conduction and relaxation properties of the current garnets are studied by impedance spectroscopy (IS) measurements. The SPS-875 garnets exhibit the highest total Li ionic conductivity of 1.25 × 10(-6) S/cm at RT, which is in the same range as the LLT garnets prepared by conventional sintering technique. The high conductivity of SPS-875 sample is due to the enhanced mobility of Li ions by one order of magnitude compared to SPS-850 and SPS-900 ceramics. The concentration of mobile Li(+) ions, n c, and their mobility are estimated from the analysis of the conductivity spectra at different temperatures. n c is found to be independent of temperature for the SPS nanoceramics, which implies that the conduction process is controlled by the Li(+) mobility. Interestingly, we found that only a small fraction of lithium ions of 3.9% out of the total lithium content are mobile and contribute to the conduction process. Moreover, the relaxation dynamics in the investigated materials have been studied through the electric modulus formalism.

No MeSH data available.


XRD patterns of Li5La3Ta2O12powder and SPS nanoceramics.
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Fig1: XRD patterns of Li5La3Ta2O12powder and SPS nanoceramics.

Mentions: X-ray powder diffraction patterns of the investigated materials are shown in Figure 1. All the spark plasma sintered samples show similar XRD patterns as the standard patterns of LLT with no secondary phases observed [1]. The SEM micrographs of the sintered ceramics are shown in Figure 2, which indicates that the SPS-850, SPS-875, and SPS-900 LLT ceramics have nano-sized grains with a grain size of 50 to 100 nm. These results indicate that spark plasma sintering produces nanoceramics of LLT garnet materials with considerably reduced grain size compared to the conventionally sintered ceramics that usually have coarse grained ceramics with grain size in the micrometer range [5,9,11].Figure 1


Lithium ionic conduction and relaxation dynamics of spark plasma sintered Li5La3Ta2O12 garnet nanoceramics.

Ahmad MM - Nanoscale Res Lett (2015)

XRD patterns of Li5La3Ta2O12powder and SPS nanoceramics.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385244&req=5

Fig1: XRD patterns of Li5La3Ta2O12powder and SPS nanoceramics.
Mentions: X-ray powder diffraction patterns of the investigated materials are shown in Figure 1. All the spark plasma sintered samples show similar XRD patterns as the standard patterns of LLT with no secondary phases observed [1]. The SEM micrographs of the sintered ceramics are shown in Figure 2, which indicates that the SPS-850, SPS-875, and SPS-900 LLT ceramics have nano-sized grains with a grain size of 50 to 100 nm. These results indicate that spark plasma sintering produces nanoceramics of LLT garnet materials with considerably reduced grain size compared to the conventionally sintered ceramics that usually have coarse grained ceramics with grain size in the micrometer range [5,9,11].Figure 1

Bottom Line: The grain size of the SPS nanoceramics is in the 50 to 100 nm range, indicating minimal grain growth during the SPS experiments.Interestingly, we found that only a small fraction of lithium ions of 3.9% out of the total lithium content are mobile and contribute to the conduction process.Moreover, the relaxation dynamics in the investigated materials have been studied through the electric modulus formalism.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, College of Science, King Faisal University, Hofuf, Al-Ahsaa, 31982 Saudi Arabia ; Physics Department, Faculty of Science, Assiut University in The New Valley, El-Kharga, The New Valley, 72511 Egypt.

ABSTRACT
In the present work, nanoceramics of Li5La3Ta2O12 (LLT) lithium ion conductors with the garnet-like structure are fabricated by spark plasma sintering (SPS) technique at different temperatures of 850°C, 875°C, and 900°C (SPS-850, SPS-875, and SPS-900). The grain size of the SPS nanoceramics is in the 50 to 100 nm range, indicating minimal grain growth during the SPS experiments. The ionic conduction and relaxation properties of the current garnets are studied by impedance spectroscopy (IS) measurements. The SPS-875 garnets exhibit the highest total Li ionic conductivity of 1.25 × 10(-6) S/cm at RT, which is in the same range as the LLT garnets prepared by conventional sintering technique. The high conductivity of SPS-875 sample is due to the enhanced mobility of Li ions by one order of magnitude compared to SPS-850 and SPS-900 ceramics. The concentration of mobile Li(+) ions, n c, and their mobility are estimated from the analysis of the conductivity spectra at different temperatures. n c is found to be independent of temperature for the SPS nanoceramics, which implies that the conduction process is controlled by the Li(+) mobility. Interestingly, we found that only a small fraction of lithium ions of 3.9% out of the total lithium content are mobile and contribute to the conduction process. Moreover, the relaxation dynamics in the investigated materials have been studied through the electric modulus formalism.

No MeSH data available.