Memory Effect on the Synthesis of Perovskite-Type Li-Ion Conductor Li_xLa_2/3–x/3TiO₃ (LLTO)

The structural chemistry of the solid ion-conducting Li x La 2/3– x /3 TiO 3 (LLTO) is rich with various polymorphs related to atomic segregation. We explored the LLTO reaction pathway from various structurally related precursors (La 2 LiO 3 H, Li 2 TiO 3, and Li 4 Ti 5 O 12 ), 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 °C is due to the presence of multiple competing low-energy phases that result in competitive byproduct formation. In all syntheses where T = 1300 °C, LLTO was the sole product; however, varying phase fractions of I 4/ mcm and P 4/ nbm polymorphs and double-perovskite P 4/ mmm can be obtained depending on the synthesis route. This is an unusual result as at 1300 °C, LLTO should only be the ideal cubic Pm -3 m perovskite structure, yet there appears to be a memory effect from the different precursors resulting in the unique phase selectivity and stabilization.