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A new type of layered Li-Mn-oxide with heavy stacking faults has been synthesized via flocculation of delaminated MnO 2 nanosheets with Li ions. Flocculated products were characterized by powder X-ray diffraction, thermal analysis, scanning electron microscopy, transmission electron microscopy, chemical analysis, N 2 adsorption, and electrochemical measurements. Chemical analysis and X-ray diffraction results indicated that the colloidal MnO 2 nanosheets were restacked to produce a lamellar material Li 0.36 MnO 2 ‚1.15H 2 O with a basal distance of 0.72 nm. Simulation of the X-ray diffraction profile suggested that the sheet-to-sheet registry was nearly random with partial order (20-40%) involving a shift vector of ( 1 / 3 , 2 / 3 , 1). A disordered mesoporous texture was resulted via the stacking of a limited number of the sheets and irregular aggregation of the resulting restacked crystallites. The structure proved to be stable during low-temperature soft-chemical synthetic processes while thermo-metastable upon heat treatment. A dehydrated sample of this new layered Li-Mn-oxide underwent electrochemical Li + insertion/extraction behavior with smooth cycling curves.

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The magnetic properties and the crystal structure of MgV2O4 and Mg(V0.85Al0.15)2O4 have been studied. Both compounds are the normal cubic spinels with highly frustrated magnetic lattice. Around T2=65 K, MgV2O4 has magnetic orders accompanied with the cubic-tetragonal transition. Below T2, the susceptibility shows complex behavior. In Mg(V0.85Al0.15)2O4, the spin-glasslike state appears. The V51-Knight shift of MgV2O4 has an anomalous temperature dependence, which is not simply related by that of the susceptibility.

We study the photo-induced insulator-metal transition in VO 2 , correlating threshold and dynamic evolution with excitation wavelength. In high-quality single crystal samples, we find that switching can only be induced with photon energies above the 670-meV gap. This contrasts with the case of polycrystalline films, where formation of the metallic state can also be triggered with photon energies as low as 180 meV, well below the bandgap. Perfection of this process may be conducive to novel schemes for optical switches, limiters and detectors, operating at room temperature in the mid-IR.