Ga-substituted Li7La3Zr2O12: An investigation based on grain coarsening in garnet-type lithium ion conductors

Gallium substituted garnet-type Li7La3Zr2O12 has been synthesized via a sol-gel (SG) and solid-state reaction (SSR) routes. The results of scanning electron spectroscopy measurements showed that the SG process produced statistically smaller powder particles than the SSR route. A structural transformation from tetragonal to cubic phase occurs at an elevated level of Gallium doping, resulting in a cubic structure for Li5.5La3Zr2Ga0.5O12 (0.5Ga-LLZO). To facilitate the comparison of sintering procedures, powders of Ga-doped LLZO were sintered by both a conventional sintering process and a spark plasma sintering (SPS) process. For pellets sintered by SPS at 950 degrees C for 5 min, grain coarsening was limited due to the short sintering duration. However, grain coarsening was observed in the SPS pellets sintered at 950 degrees C, 1000 degrees C, and 1100 degrees C for 5 h in air. The ionic conductivity was determined by electrochemical impedance spectroscopy (EIS) at temperatures in the range of 20 degrees C-100 degrees C. The total ionic conductivity was found to increase with increased relative density and larger grain size. The highest total ionic conductivity at room temperature was found to be in the range of 5.81 x 10(-5) S/cm (Ea = 0.41 eV) in this work. (C) 2016 Elsevier B.V. All rights reserved.