Memory Effect on the Synthesis of Perovskite-Type Li-Ion Conductor Li x La2/3-x/3TiO3 (LLTO)

The structural chemistry of the solid ion-conducting LixLa2/3-x/3TiO3 (LLTO) is rich with various polymorphs related to atomic segregation. We explored the LLTO reaction pathway from various structurally related precursors (La2LiO3H, Li2TiO3, and Li4Ti5O12), focusing on the effects of LLTO-like structural motifs in precursors using a combination of experimental and computational techniques. Density functional theory (DFT) calculations revealed that the failure of syntheses to produce LLTO below 1300 degrees C is due to the presence of multiple competing low-energy phases that result in competitive byproduct formation. In all syntheses where T = 1300 degrees C, LLTO was the sole product; however, varying phase fractions of I4/mcm and P4/nbm polymorphs and double-perovskite P4/mmm can be obtained depending on the synthesis route. This is an unusual result as at 1300 degrees C, LLTO should only be the ideal cubic Pm-3m perovskite structure, yet there appears to be a memory effect from the different precursors resulting in the unique phase selectivity and stabilization.