Effect of microstructural ordering and domain on the mechanical behavior of Li0.33La0.557TiO3

Li 0.33 La 0.557 TiO 3 (LLTO) is a promising candidate electrolyte for all-solid-state batteries. LLTO has an ordered crystal structure along the c -axis, which forms microdomain structures. We investigated the mechanical behavior of LLTO with microstructures with different ordering and domain structures under four-point bending, aiming to elucidate the role of domains in deformation and fracture. Tetragonal LLTO with domains consisting of ordered crystal structures exhibited an almost linear elastic response, which was consistent for all degrees of ordering within the investigated range. By contrast, cubic LLTO without domains exhibited anomalously nonlinear behavior with strong hysteresis. Cubic LLTO had a much lower modulus than tetragonal LLTO. In-situ XRD under bending confirmed an increase of anisotropy and preferential orientation for tetragonal and cubic phases, respectively. Fractography confirmed overall transgranular fracture but with domain-like structures on the fracture surface for both tetragonal and cubic LLTOs. The lower modulus and hysteresis of cubic LLTO may be attributed to non-diffusional deformation accompanied by stress-induced formation of domain-like structures during loading and their disappearance upon unloading, respectively.