Spherical nanosize Ag/SiO2 composite particles have been synthesized within reverse micelles via metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethoxysilane (TEOS) within the microemulsion. Composite particles in the size range 20−35 nm are produced. As the molar ratio of water to surfactant is increased above 10, the size distribution broadens. Absorption spectra have been used to dynamically monitor the reaction and growth. The effects of other synthesis parameters, such as the molar ratio of water to TEOS and the amount of base catalyst, are discussed. Possible mechanisms for the formation of the nanocomposite particles are also discussed.

The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

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Prussian blue analogues (PBAs) have recently been proposed as electrode materials for low-cost, long-cycle-life, and high-power batteries. However, high-capacity bimetallic examples show poor cycle stability due to surface instabilities of the reduced states. The present work demonstrates that, relative to single-component materials, higher capacity and longer cycle stability are achieved when using Prussian blue analogue core@shell particle heterostructures as the cathode material for Li-ion storage. Particle heterostructures with a size dispersion centered at 210 nm composed of a high-capacity K(0.1)Cu[Fe(CN)(6)](0.7)·3.8H(2)O (CuFe-PBA) core and lower capacity but highly stable shell of K(0.1)Ni[Fe(CN)(6)](0.7)·4.1H(2)O have been prepared and characterized. The heterostructures lead to the coexistence of both high capacity and long cycle stability because the shell protects the otherwise reactive surface of the highly reduced state of the CuFe-PBA core. Furthermore, interfacial coupling to the shell suppresses a known structural phase transition in the CuFe-PBA core, providing further evidence of synergy between the core and shell. The structure and chemical state of the heterostructure during electrochemical cycling have been monitored with ex situ X-ray diffraction and X-ray absorption experiments and compared to the behavior of the individual components.

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Langmuir-Blodgett (LB) films of a series of divalent metal octadecylphosphonates have been prepared and characterized. The films are each shown to be LB analogs of known solid-state metal phosphonates possessing 2-dimensional ionic-covalent metal phosphonate layers. The metal phosphonate layers crystallize during the LB deposition process. Films were characterized with XPS, X-ray diffraction, ellipsometry, attenuated total reflectance FTIR, and, in the case of the manganese film, SQUID magnetometry. Octadecylphosphonate films with Mn 2+ , Mg 2+ , and Cd 2+ form with the stoichiometry M(O 3 PC 17 H 37 )‚H 2 O and have metal phosphonate bonding consistent with the analogous M(O 3 PR)‚H 2 O layered solids. The Ca 2+ film forms as Ca(HO 3 PC 18 H 37 ) 2 , which is also a known solid-state phase. Magnetic measurements reveal that the manganese octadecylphosphonate film undergoes a magnetic ordering transition at 13.5 K resulting in a "weak ferromagnet". The behavior is similar to that of the known layered solid-state manganese alkylphosphonates which are also "weak ferromagnets". The magnetic ordering is antiferromagnetic where incomplete cancellation of the magnetic sublattices, due to low site symmetry, results in a spontaneous magnetization. A spin-flop transition is observed at 2.5 T in magnetization Vs applied field measurements of the ordered state. The film also exhibits magnetic memory, with a small remnant magnetization and a coercive field of 20 mT at 2 K. The results demonstrate that magnetic ordering phenomena can be incorporated into LB films and that LB film methods can be used to prepare monolayer and multilayer films of known solid-state materials.

Heterostructured ABA thin films consisting of two different Prussian blue analogues, where A is a ferromagnet and B is a photoinducible ferrimagnet, have been fabricated for the first time. This novel arrangement allows the magnetization to be decreased by irradiation with white light and significantly increases the ordering temperature of the photoinduced magnetism from 18 to 75 K.

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