A mixed alkali metal titanate with the lepidocrocite-like layered structure. Preparation, crystal structure, protonic form, and acid-base intercalation properties

A mixed alkali metal titanate of composition A_xTi_2-x/3Li_x/3O₄ (A = K, Rb, Cs) has been prepared and its ion-exchange/intercalation properties have been explored. Solid-state calcination of appropriate mixtures of TiO₂ and alkali metal carbonates produced the titanate at a stoichiometry of x = 0.80 for A = K, 0.75 for Rb, and 0.70 for Cs. Rietveld refinement on neutron diffraction data confirmed that the orthorhombic structure is comprised of lepidocrocite-related host layers of Ti_2-x/3Li_x/3O₄ and charge-balancing A ions in the interlayer domain. Complete extraction of both alkali metal ions was achieved by acid-leaching, producing a new protonic titanate of H_4x/3Ti_2-x/3O₄·H₂O. This phase is distinguished from isomorphous related compounds in terms of high proton content as a consequence of exchangeable Li ions located in the host framework. The material took up alkali metal ions and organoammonium ions from aqueous media. These ion-exchange and intercalation reactions brought about expansion/contraction of the gallery height and lateral displacement of the layers. The resulting various types of layer sequence can be understood in terms of the nature of the interlayer species.