Defect crystal structure of new TiO(OH)2 hydroxide and related lithium salt Li2TiO3

Abstract

Crystal structures of TiO(OH)₂ and Li₂TiO₃ have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li₂TiO₃ salt obtained at 700 °C reveals stacking faults of LiTi₂ metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3₁12. The possibility to stabilise this imperfect state increases the mobility of the Li⁺ ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)₂. The crystal structure of TiO(OH)₂ belongs to the layered double hydroxide structure type with the 3R₁ sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)₂OTi₂O(OH)₂]. TiO(OH)₂ is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.