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International audience; Temperature-dependent specific heat, magnetization and neutron diffraction data have been collected in zero magnetic field for polycrystalline samples of MnW1−x Mo x O4 (x ≤ 0.2) solid solution whose end-member MnWO4 exhibits a magnetoelectric multiferroic phase (AF2 phase) between T 1 ≈ 8 K and T 2 = 12.5 K. In MnW1−x Mo x O4, diamagnetic W6+ are replaced with diamagnetic Mo6+ cations and magnetic couplings among Mn2+ (3d 5, S = 5/2) ions are modified due the doping-induced tuning of the orbital hybridization between Mn 3d and O 2p states. It was observed that magnetic phase transition temperatures which are associated with the second-order AF3-to-paramagnetic (T N) and AF2-to-AF3 (T 2) transitions in pure MnWO4 slightly increase with the Mo content x. Magnetic specific heat data also indicate that the first-order AF1-to-AF2 phase transition at T 1 survives a weak doping x ≤ 0.05. This latter phase transition becomes invisible above the base temperature 2 K for higher level of doping x ≥ 0.10. Neutron powder diffraction datasets collected above 1.5 K for a sample of MnW0.8Mo0.2O4 were analyzed using the Rietveld method. The magnetic structure below ≈ 14 K is a helical incommensurate spin order with a temperature-independent propagation vector k = (−0.217(6), 0.5, 0.466(4)). This cycloidal magnetic structure is similar to the polar AF2 structure observed in MnWO4. The AF1 up-up-down-down collinear spin arrangement observed in MnWO4 is absent in our MnW0.8Mo0.2O4 sample.

Pulsed laser deposition (PLD) was used to prepare substitutionaly disordered Pt3Sc. Deposition was performed by using a crossed-beam PLD setup and the laser intensity on the Pt and Sc targets was adjusted to reach the desired composition (Pt:Sc 3:1). Deposition was performed in vacuum, 133 Pa He and 133 Pa Ar, on both Cu and Si substrates. It was shown that a homogeneous and substitutionaly disordered Pt3Sc alloy is formed when deposition is performed in vacuum and 133 Pa Ar on a Cu substrate. Alternatively, a non-homogeneous and multilayered deposit is formed when deposition is performed in vacuum on a Si substrate. This is believed to arise as a consequence of re-sputtering (and decomposition) of the native silicon oxide when highly energetic ablated species impinge on the substrate. The kinetic energy of the ablated species is reduced by increasing the pressure of Ar in the deposition chamber, yielding to an increased stability of the native silicon oxide layer and the formation of a porous deposit made of substitutionaly disordered Pt3Sc. The same phenomenon is observed when deposition is performed on a Ti substrate.

The effect of aluminum addition on the structural and low-temperature oxidation behavior of commercially available MoSi2 was investigated by means of X-ray diffraction and thermogravimetric analysis. MoSi2 + x Al compounds (with x = 0.0, 0.10, 0.20, 0.30, and 0.40) were mechanically processed for 6 h starting from α-MoSi2 and Al powders. It is shown that Al can substitute Si atoms in pre-formed MoSi2 leading to the formation of β-MoSi2 (the high temperature phase). The unit cell volume of β-MoSi2 increases linearly with the Al content. For x

International audience; The influence of magnetic field on the dielectric properties of several Mn1-x(Mg,Zn)xWO4 multiferroic ceramics is investigated, and confirms an additional phase transition below the ferroelectric Curie temperature previously detected in this system in zero magnetic field. In highly doped samples an original plateau of the capacitance is observed between T2 and this additional transition. Pyroelectric measurements in zero magnetic field for a Mn0.85Mg0.15WO4 ceramic confirm the existence of this unexpected low temperature phase transition. The magnetic or structural origin of this transition is discussed.

Four new ABZrF7 heptafluorozirconates (A = Rb, Tl; B = Ca, Cd) and their homologous heptafluorohafnates, all colorless, orthorhombic Cmcm (no63), Z = 4, have been synthesized by heating stoichiometric mixtures of RbF or TlF, CaF2 or CdF2 and ZrF4 (HfF4) in sealed platinum tubes at temperature ranging from 550 °C (Tl) to 600 °C (Rb). The crystal structures of both RbCdZrF7 and TlCdZrF7 have been solved from single-crystal X-rays diffraction data. Rietveld refinements were performed from X-rays powder patterns for RbCaZrF7 and TlCaZrF7. In this series of heptafluorides, both B2+ and Zr4+ cations exhibit a pentagonal bipyramidal 7-coordination. Their structural relationships with other heptafluorozirconates AIBIIZrF7 as well as β-KYb2F7 are discussed. RbCaZrF7: a = 6.863(1) A, b = 11.130(1) A, c = 8.485(1) A; TlCaZrF7: a = 6.868(1) A, b = 11.165(1) A, c = 8.486(1) A; RbCdZrF7: a = 6.780(1) A, b = 11.054(4) A, c = 8.420(4) A; TlCdZrF7: a = 6.784(3) A, b = 11.099(2) A, c = 8.424(9) A.

International audience; Ceramic samples of MnW1-xMoxO4 (x ≤ 0.3) solid solution were prepared by a solid-state route with the goal of increasing the magnitude of the spin-exchange couplings among the Mn2+ ions in the spin spiral multiferroic MnWO4. Samples were characterized by X-ray diffraction, optical spectroscopy, magnetization, and dielectric permittivity measurements. It was observed that the Néel temperature TN, the spin spiral ordering temperature TM2, and the ferroelectric phase-transition temperature TFE2 of MnWO4 increased upon the nonmagnetic substitution of Mo6+ for W6+. Like pure MnWO4, the ferroelectric critical temperature TFE2(x) coincides with the magnetic ordering temperature TM2(x). A density functional analysis of the spin-exchange interactions for a hypothetical MnMoO4 that is isostructural with MnWO4 suggests that Mo substitution increases the strength of the spin-exchange couplings among Mn2+ in the vicinity of a Mo6+ ion. Our study shows that the Mo-doped MnW1-xMoxO4 (x ≤ 0.3) compounds are spin-frustrated materials that have higher magnetic and ferroelectric phase-transition temperatures than does pure MnWO4.

Four new ABZrF7 heptafluorozirconates (A = Rb, Tl; B = Ca, Cd) and their homologous heptafluorohafnates, all colorless, orthorhombic Cmcm (no63), Z = 4, have been synthesized by heating stoichiometric mixtures of RbF or TlF, CaF2 or CdF2 and ZrF4 (HfF4) in sealed platinum tubes at temperature ranging from 550 °C (Tl) to 600 °C (Rb). The crystal structures of both RbCdZrF7 and TlCdZrF7 have been solved from single-crystal X-rays diffraction data. Rietveld refinements were performed from X-rays powder patterns for RbCaZrF7 and TlCaZrF7. In this series of heptafluorides, both B2+ and Zr4+ cations exhibit a pentagonal bipyramidal 7-coordination. Their structural relationships with other heptafluorozirconates AIBIIZrF7 as well as β-KYb2F7 are discussed. RbCaZrF7: a = 6.863(1) A, b = 11.130(1) A, c = 8.485(1) A; TlCaZrF7: a = 6.868(1) A, b = 11.165(1) A, c = 8.486(1) A; RbCdZrF7: a = 6.780(1) A, b = 11.054(4) A, c = 8.420(4) A; TlCdZrF7: a = 6.784(3) A, b = 11.099(2) A, c = 8.424(9) A.

Editeur Elsevier; Layered double hydroxide (LDH) organo-modified by a surface-active monomer, 3-sulfopropyl methacrylate (SPMA) was used as filler for polystyrene (PS). DifFerent nanocomposites SPMA/LDH:PS were prepared by bulk polymerization process using low amount of initiator. The two components, filler and polymer, as well as the degree dispersion of the reactive filler as a function of ils loading in PS were characterized by a combination of several techniques: X-ray diffraction, high resolution t3C CP-MAS NMR, 1-TIR, UV-visible, thermal analysis, SEC and MET. The nanocomposites were submitted to UV-light exposures in the presence of oxygen. The oxidation photoproducts and the rates of oxidation were compared for the varions samples. It was shown that the filler was not modifying the oxidation mechanism of the polymer, but had a slight effect on the oxidation rate.