Synergistic Modulation of Grain Boundary and Domain Boundary Enhances the Ionic Conductivity of Li_0.33La_0.56TiO₃ Solid Electrolyte

The ABO₃ perovskite oxide solid state electrolyte Li_3<i>x</i>La_2/3-<i>x</i>TiO₃ (LLTO) has gained significant attention. Despite their potential, both the bulk and grain boundary conductivity values observed in practice fall short of theoretical expectations. In terms of structures, domain boundaries and grain boundaries play a crucial role in hindering ionic transport, and there has been no comprehensive study that enhances both the bulk and grain boundary conductivity by modification of these microstructures. Here, we have employed the multiscale method and demonstrated that Ta and Sr codoping strategy balances the structural symmetry, Li⁺ concentration, grain boundaries, domain boundaries, and the lattice defects, which simultaneously enhances the bulk and grain boundary conductivity. The highest total ionic conductivity achieved is 3.0 × 10^-4 S cm^-1 in the Li_0.33La_0.54Sr_0.03Ti_0.9625Ta_0.03O₃ sample, with an 280% enhancement over the pristine sample. Our work highlights the coupling effects of domain and grain boundaries for further improving the ionic conductivity of perovskite solid state electrolyte.