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

Mohamad M Ahmad

doi:10.1186/s11671-015-0777-7

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, nc, and their mobility are estimated from the analysis of the conductivity spectra at different temperatures. nc 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.

Highlights

Li5La3Ta2O12 (LLT) lithium ion conductors with the garnetlike structure have received considerable research interests due to their electrical, electrochemical, and mechanical properties [1,2,3,4,5,6,7,8,9,10,11,12,13]
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]
The present study confirmed that spark plasma sintering is a powerful technique to fabricate nanoceramics of different types of materials including lithium conducting garnets

Summary

Introduction

Li5La3Ta2O12 (LLT) lithium ion conductors with the garnetlike structure have received considerable research interests due to their electrical, electrochemical, and mechanical properties [1,2,3,4,5,6,7,8,9,10,11,12,13]. These materials have good ionicconductivity in the range of 10−6 S/cm at RT with small contributions from the grain boundaries and negligible electronic conductivity [1,2,3]. The ionic conductivity increases for nanostructured materials such as CaF2-BaF2 fluoride ion conductors [14], CeO2 oxide ion conducting nanoceramics [15,16], and nanocrystalline LiNbO3 and LiTaO3 lithium ion conductors [17,18]

Methods

Results

Conclusion