New titanoniobates (Li,H)2TiNbO5 and (Li,H)3TiNbO5: synthesis, structure and properties

Abstract

The electrochemical reduction of the layered titanoniobate HTiNbO₅ has allowed two new phases, (Li,H)₂TiNbO₅ and (Li,H)₃TiNbO₅, to be synthesized, the structures of which have been studied by X-ray diffraction and electron microscopy. (Li,H)₂TiNbO₅ is closely related to the LiTiNbO₅ phase, with a “parallel configuration” of the |TiNbO₆|_∞ ribbons between two successive [TiNbO₅]ⁿ⁻_n layers. One lithium could be reversibly inserted at 1.6 V for a capacity of 120 mAh g⁻¹. This phase exhibits a strong contrast in color between the charge and discharge steps, suggesting a potential electrochromic material. (Li,H)₃TiNbO₅ reveals a distorted and ordered rock salt-type structure. A structural model is proposed for the mechanism of intercalation.