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

The electrochemical reduction of the layered titanoniobate HTiNbO5 has allowed two new phases, (Li,H)(2)TiNbO5 and (Li,H)(3)TiNbO5, to be synthesized, the structures of which have been studied by X-ray diffraction and electron microscopy. (Li,H)(2)TiNbO5 is closely related to the LiTiNbO5 phase, with a parallel configuration'' of the vertical bar TiNbO6 vertical bar(infinity) 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)(3)TiNbO5 reveals a distorted and ordered rock salt-type structure. A structural model is proposed for the mechanism of intercalation.