Nanoscale control of the morphology of lithium manganate and silica composites using self-organized sol-gel media

Tetraethoxysilane-derived silica containing lithium and manganese nitrates has been prepared in solutions of poly(oxyethylene) surfactants, giving novel monolithic gels in which the metal ions are associated with the incorporated surfactant. Calcination produces nanocrystalline lithium manganate in the silica matrix. The gels and calcined phases have been characterized by X-ray diffraction and X-ray absorption near edge and extended fine structure spectroscopy at the Mn K-edge (XANES and EXAFS). At 400 degrees C the reaction between lithium and manganese is incomplete, and both nanocrystalline lithium manganate and disordered manganese in a lower-valent state are identified. Including excess lithium in the gels and calcining at 500 degrees C allows practically all the manganese in the gels to be reacted to form lithium manganate phases with manganese in a predominantly tetravalent oxidation state. Electron microscopy shows that different microstructures and particle morphologies are obtained by varying the nature and concentration of the poly(oxyethylene) agent. The method therefore not only provides a means of preparing the ternary lithium manganate phase in silica but offers new possibilities for exploiting the self-assembly properties of surfactants to produce composite materials with tailored microstructures.