Preparation of Nb-substituted titanates by a novel sol-gel assisted solid state reaction.

Single-phase layered Nb-substituted titanates, Na(2)Ti(3-x)Nb(x)O(7) (x = 0-0.06) and Cs(0.7)Ti(1.8-x)Nb(x)O(4) (x = 0-0.03), were for the first time synthesized by a novel sol-gel assisted solid state reaction (SASSR) route. Conventional solid state reactions as well as sol-gel synthesis did not succeed in producing phase pure Nb-substituted titanates. In the SASSR synthesis route we combine the advantages of traditional sol-gel technique (i.e., homogeneous products formed at low temperatures) and solid state reaction (i.e., formation of stable, crystalline phases) for preparing single-phase niobium-substituted layered titanates. The obtained products were characterized by X-ray powder diffraction, scanning electron microscopy, inductively coupled plasma-atomic emission spectrometry, Raman spectroscopy, and thermogravimetric analysis. Results indicate that the Ti(IV) in the host layer of the samples could be partially replaced by Nb(V) without structural deterioration. After proton-exchange, more water molecules were intercalated into the interlayer of H(0.7)Ti(1.8-x)Nb(x)O(4) x nH(2)O with increasing niobium content, whereas the interlayer distance of H(2)Ti(3-x)Nb(x)O(7) (x = 0-0.06) was unchanged.