Synthesis, crystal and electronic structures, and magnetic properties of LiLn9Mo16O35 (Ln = La, Ce, Pr, and Nd) compounds containing the original cluster Mo16O36

The new compounds LiLn(9)Mo(16)O(35) (Ln=La, Ce, Pr, and Nd) were synthesized from stoichiometric mixtures of Li(2)MoO(4), Ln(2)O(3), Pr(6)O(11) or CeO(2), MoO(3), and Mo heated at 1600 °C for 48 h in a molybdenum crucible sealed under a low argon pressure. The crystal structure, determined from a single crystal of the Nd member, showed that the main building block is the Mo(16)O(36) unit, the Mo(16) core of which is totally new and results from the fusion of two bioctahedral Mo(10) clusters. It can also be viewed as a fragment of an infinite twin chain of edge-sharing Mo(6) octahedra. The Mo(16)O(36) cluster units share some oxygen atoms to form infinite chains running parallel to the b axis, which are separated by the rare-earth and lithium cations. (7)Li-NMR experiments, carried out at high field on the nonmagnetic LiLa(9)Mo(16)O(35), provided insights into the local environment of the lithium ions. Magnetic susceptibility measurements confirmed the trivalent oxidation state of the magnetic rare-earth cations and indicated the absence of localized moments on the Mo(16) clusters. The electronic structure of the LiLn(9)Mo(16)O(35) compounds was analyzed using molecular and periodic quantum calculations. The study of the molecular orbital diagrams of isolated Mo(16)O(36) models allowed the understanding of this unique metallic architecture. Periodic density functional theory calculations demonstrated that few interactions occur between the Mo(16) clusters, and predicted semiconducting properties for LiLn(9)Mo(16)O(35) as a band gap of 0.57 eV was computed for the lanthanum phase.     

Indentation Behavior of Silica Optical Fibers Aged in Hot Water

Vickers indentations were performed on silica optical fibers subjected to water interaction by a hydrothermal treatment. The observation of the Vickers impression provided direct evidence of a piling-up of material of the fiber submitted to the hydrothermal treatment. This indentation behavior is consistent with a structural relaxation promoted by the water and the glass network interaction. It is suggested that the water could act as a modifier since the deformation combines the densification and the shear flow of the material. When the relaxed surface layer is chemically etched, the anomalous behavior of silica under indentation is restored as the deformation is controlled only by densification. The chemical etched samples exhibited an increase in hardness.     

Cations Insertion in Molybdenum Cluster Compounds: Electronic Structure and Electrochemical Study Using Cavity Microelectrode

Owing to the high lability of cations in the three-dimensional framework of K_1+x Mo₁₂S₁₄ (0 ≤ x ≤ 1.6), first-principles calculations and electrochemical methods have been carried out to study the insertion of cations in the empty channels of this compound. The cavity microelectrode that is a suitable electrode for powder material analysis has been used in voltammetric experiments. Results obtained for Li⁺, Na⁺, Rb⁺, K⁺, Cs⁺ and NH₄ ⁺ cations are presented and discussed.     

Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes

We report on the magnetic hyperthermia properties of chemically synthesized ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the saturation magnetization of bulk iron. The specific absorption rate measured on 16 nm nanocubes is 1690±160 W/g at 300 kHz and 66 mT. This corresponds to specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in other systems. A way to quantify the degree of optimization of any system with respect to hyperthermia applications is proposed. Applied here, this method shows that our nanoparticles are not fully optimized, probably due to the strong influence of magnetic interactions on their magnetic response. Once protected from oxidation and further optimized, such nano-objects could constitute efficient magnetic cores for biomedical applications requiring very large heating power.     

NMR study of the structure and properties of poly(MMA-co-VP) crosslinked hydrogels

¹H- and ¹³C-NMR techniques were used to study the microscopic structure of NMA/VP copolymer hydrogels. Evidence was obtained for a plasticization effect of MMA chains by VP. An original ¹H-NMR approach revealed the existence of several types of water with various degree of bounding to the polymer network, a conclusion that is corroborated by a complementary ¹³C-NMR study. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3619–3625, 1997     

Influence of barium on the Co modification of γ=Fe2)3 particles derived from oxalic precursors

Acicular γFe₂O₃ core particles were derived from Ba-doped iron oxalate. Ba was located at the surface of the oxide particles, which were the modified by the cobalt epitaxial method. Coercivities as high as 800 Oe were observed with a temperature coefficient of 0.35% /K. The presence of barium did not slow down the diffusion of cobalt inside the particle during ageing.