A mixed alkali metal titanate of composition A x Ti 2-x/3 Li x/3 O 4 (A ) K, Rb, Cs) has been prepared and its ion-exchange/intercalation properties have been explored. Solid-state calcination of appropriate mixtures of TiO 2 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/3 Li x/3 O 4 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/3 Ti 2-x/3 O 4 ‚H 2 O. 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.

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Powder Na x CoO 2 (0:70 x 0:84) samples were synthesized and characterized carefully by X-ray diffraction analysis, inductive-coupled plasma atomic emission spectroscopy, and redox titration. It was proved that -Na x CoO 2 is formed only in the narrow range of 0:70 x 0:78. Nevertheless, the magnetic properties depend strongly on x. We found, for the first time, two characteristic features in the magnetic susceptibility of Na 0:78 CoO 2 , a sharp peak at T p ¼ 16 K and an anomaly at T k ¼ 9 K, as well as the transition at T c ¼ 22 K and the broad maximum at T m ¼ 50 K which had already been reported. A type of weak ferromagnetic transition seems to occur at T k . The transition at T c , which is believed to be caused by spin density wave formation, was observed clearly for x ! 0:74 with constant T c and T p independent of x. On the other hand, ferromagnetic moment varies systematically depending on x. These facts suggest the occurrence of a phase separation at the microscopic level, such as the separation into Na-rich and Na-poor domains due to the segregation of Na ions. The magnetic phase diagram and transition mechanism proposed previously should be reconsidered.