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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.


Representative complex impedance diagrams at different temperatures of SPS LLT nanoceramics. (a) SPS-850, (b) SPS-875, and (c) SPS-900 nanoceramics.
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Fig3: Representative complex impedance diagrams at different temperatures of SPS LLT nanoceramics. (a) SPS-850, (b) SPS-875, and (c) SPS-900 nanoceramics.

Mentions: The electrical properties of the investigated materials have been studied through impedance spectroscopy measurements. Representative complex impedance diagrams of the SPS ceramics are shown in Figure 3 at selected temperatures. The impedance diagrams show one semicircle at the high frequency region that could not be separated to grain and grain boundary contributions. Therefore, the intercept of the semicircle with the real axis represents the total (grain + grain boundary) ionic conductivity. At low frequencies, a large spike is observed which originates from electrode polarization effects and becomes more prominent at higher temperatures. The temperature dependence of the ionic conductivity of the SPS samples is shown in Figure 4. The values of the total conductivity at 27°C for the investigated materials are listed in Table 1. The total ionic conductivity first increases by one order of magnitude with increasing the SPS temperature from a value of 2.98 × 10−7 S/cm for the SPS-850 sample to 1.25 × 10−6 S/cm for the SPS-875 sample. With further increase of the SPS temperature to 900°C, the conductivity drops to 1.3 × 10−7 S/cm. The conductivity value of the SPS-875 nanoceramics in the present work is similar to the values reported previously for conventionally sintered LLT samples prepared either by solid state reaction or sol-gel techniques and sintered at 950°C and 900°C, respectively [1,11].Figure 3


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

Ahmad MM - Nanoscale Res Lett (2015)

Representative complex impedance diagrams at different temperatures of SPS LLT nanoceramics. (a) SPS-850, (b) SPS-875, and (c) SPS-900 nanoceramics.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Representative complex impedance diagrams at different temperatures of SPS LLT nanoceramics. (a) SPS-850, (b) SPS-875, and (c) SPS-900 nanoceramics.
Mentions: The electrical properties of the investigated materials have been studied through impedance spectroscopy measurements. Representative complex impedance diagrams of the SPS ceramics are shown in Figure 3 at selected temperatures. The impedance diagrams show one semicircle at the high frequency region that could not be separated to grain and grain boundary contributions. Therefore, the intercept of the semicircle with the real axis represents the total (grain + grain boundary) ionic conductivity. At low frequencies, a large spike is observed which originates from electrode polarization effects and becomes more prominent at higher temperatures. The temperature dependence of the ionic conductivity of the SPS samples is shown in Figure 4. The values of the total conductivity at 27°C for the investigated materials are listed in Table 1. The total ionic conductivity first increases by one order of magnitude with increasing the SPS temperature from a value of 2.98 × 10−7 S/cm for the SPS-850 sample to 1.25 × 10−6 S/cm for the SPS-875 sample. With further increase of the SPS temperature to 900°C, the conductivity drops to 1.3 × 10−7 S/cm. The conductivity value of the SPS-875 nanoceramics in the present work is similar to the values reported previously for conventionally sintered LLT samples prepared either by solid state reaction or sol-gel techniques and sintered at 950°C and 900°C, respectively [1,11].Figure 3

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.