Chessboard-like nanostructure evolution in Li0.48Nd0.5TiO2.99 perovskites and its effects on electrochemical properties

Lithium neodymium titanate ABO₃ perovskites have been synthesized by a solid-state synthesis route. All the samples sintered at 1250°C for 24 h followed by slow cooling at ∼ 10°C h⁻¹ undergo an ordering−induced polymorphic transformation where the amount of ordering increases as the A site cation vacancy content increases. Li_0.48Nd_0.5TiO_2.99 sintered at 1250°C for 24 h and then quenched to room temperature forms a Pnma orthorhombic phase. This phase is also observed after 100 charging and discharging cycles of the Li_0.48Nd_0.5TiO_2.99 sample sintered at 1250°C and then slow-cooled.

A chessboard-like nanostructure with a ∼7 nm × 7 nm domain size is observed in the sintered and slow-cooled Li_0.48Nd_0.5TiO_2.99, forming along {001} or {010} interfaces of the pseudo-tetragonal crystal structure. In the slow-cooled sample, independent channels of Li-ions, Nd-ions, and mixed ions are observed in the [100] projection of this chessboard-like structure. The atom probe tomographic reconstruction of this phase clearly indicates phase separation, with a periodic variation of the Li, Nd, and Ti ions. Significantly, the electrochemical properties of this Li_0.48Nd_0.5TiO_2.99 material are superior to those of sintered and quenched Li_0.48Nd_0.5TiO_2.99 and those of sintered and slow-cooled Li_0.36Nd_0.5TiO_2.93, neither of which exhibit a chessboard-like nanostructure.