Effect of Ga+3 Substitution on The Ionic Conduction and Relaxation Properties of Li5+2xLa3Ta2-xGaxO12 Lithium Ionic Conductors

Abstract

Solid-state lithium ionic conductors are interesting materials for application in all solid-state lithium ion batteries. In this regards, Li5La3Ta2O12 (LLT) lithium ion conductors with the garnet-like structure have attained considerable interest due to their high ionic conductivity and chemical and thermal stability. In the current work, we studied the effect of Ga+3 substitution on the Ta+5 site in Li5+2xLa3Ta2-xGaxO12 (LLTGa, x = 0 – 0.50) in order to enhance the lithium ionic conductivity of the garnet materials. We found that considerable enhancement of the lithium ionic conductivity is achieved in these garnets. In Li5.6La3Ta1.7Ga0.3O12 garnets, for example, the ionic conductivity increased by about one orders of magnitude to a value of 4 × 10−5 S/cm compared to the LLT pure phase. We have been using mechanical milling techniques and solid state reaction for the preparation of the current material. The ceramics samples of the investigated materials are prepared via two techniques; the conventional sintering (CS) and spark plasma sintering (SPS) techniques at different temperatures. We have characterized the product materials by standard techniques including X-ray diffraction and scanning electron microscopy (SEM) for structural and microstructure study. The electrical (Ionic conduction) and relaxation properties of the product materials will be studied by impedance spectroscopy over wide ranges of temperature and frequency. The impedance, electric modulus, conductivity, and dielectric permittivity data will be thoroughly analyzed by appropriate equivalent circuits and theoretical models in order to understand the origin of the ionic conductivity. Moreover, the dielectric properties were studied for the current materials. All of the garnet materials exhibit giant values of the dielectric constant of ε’ > 1000. We show that this giant values of ε’ were attained not due to interfacial polarization at the sample/electrode interfaces, but due to some internal effects in the materials.