Exaggerated grain growth and the development of coarse-grained microstructures in lithium lanthanum titanate perovskite ceramics
Petruša Borštnar, Jan Žuntar, Matjaž Spreitzer, Goran Dražić, Nina Daneu
Abstract
Li3xLa2/3−x⎕1/3–2xTiO3 (LLTO) ceramics is recognized as one of the most promising solid electrolytes for applications in all-solid-state batteries. The total ionic conductivity is usually diminished by the contribution of grain boundaries, therefore microstructures with larger grain sizes are desirable. In this work we prepared compositions with slightly decreased TiO2 additions, i.e. increased La:Ti ratio, and triggered the formation of Ruddlesden-Popper type sequences with structural elements of the Li2La2Ti3O10 phase within the matrix perovskite LLTO grains as revealed by HAADF-STEM. These grains exhibit exaggerated grain growth (EGG), which initially results in the development of bimodal microstructures. At higher sintering temperatures, grain growth continues by enhanced coarsening via Ostwald ripening and the RP-type sequences recrystallize to perovskite LLTO. This results in the development of dense microstructures with LLTO grains measuring up to 100 µm in diameter. The findings represent a novel and straightforward approach for the preparation of coarse-grained LLTO ceramics.