Epitaxial Strain-Controlled Ionic Conductivity in Li-Ion Solid Electrolyte Li0.33La0.56TiO3 Thin Films

Ionic conductive Li0.33La0.56TiO3 (LLT) epitaxial thin films were grown on perovskite SrTiO3 (100), NdGaO3 (HO), and (LaAlO3)(0.3)-(SrAl0.5Ta0.5O3)(0.7) (100) single crystal substrates by pulsed laser deposition. The use of Li-rich Li0.84La0.56TiO3+delta target together with an optimized laser fluence resulted in the growth of phase pure LLT thin films with high growth rate of 2 nm/min. The a-axis and c-axis oriented films were selectively grown by choosing the substrates. Ionic conductivity at room temperature of LLT epitaxial film on NdGaO3 (110) substrate was close to that of bulk previously reported, representing the highly crystalline quality. In addition, the unequally strained lattice due to different inplane lattice constants of orthorhombic NdGaO3 substrate resulted in laterally anisotropic ionic conductivity with different activation energy perpendicular to NdGaO3 [110] and [001], 6.7 x 10(-4) S.cm(-1) with 0.34 eV and 4.3 x 10(-4) S.cm(-1) with 0.36 eV, respectively. This result suggests that the lattice engineering can provide a way to control Li ionic conduction.