82 research outputs found
High-pressure synthesis, structural and complex magnetic properties of the ordered double perovskite Pb2NiReO6
The ordered double perovskite Pb2NiReO6 has been prepared at 6 GPa and temperatures ranging from 1273 to 1373 K. Its crystal structure determined by X-ray powder diffraction and selected area electron diffraction shows monoclinic symmetry with centrosymmetric space group I2/m (a = 5.6021(1) Å, b = 5.6235(1) Å, c = 7.9286(1) Å and β = 90.284°(1)). High angle annular dark field microscopy studies reveal the existence of compositional microdomains. The compound displays a re-entrant spin-glass transition from a ferrimagnetic ordering below TN 37 K between the Re+5 and Ni+3 (high spin configuration) magnetic sublattices to a spin-glass configuration. Magnetic field dependent magnetization measurements revealed wasp-waisted hysteresis loops at 5 K. These shaped features originate from the antiferromagnetic/ferromagnetic (AFM/FM) competing interactions
Stereoselective Synthesis of 1-Hydroxymethyl-4-phenylsulfonylbutadienes
Reactividad de sulfonas para la obtención de sistemas dienicos.[ES]Reactividad de sulfonas para la obtención de sistemas dienicos.CICYT, Junta Castilla y
Leon (SA 44-96) y Ministerio de Educación y Cienci
Double double cation order in the high pressure perovskites MnRMnSbO6
International audienceCation ordering in ABO3 perovskites adds to their chemical variety and can lead to properties such as ferrimagnetism and magnetoresistance in Sr2FeMoO6. Through high-pressure and high-temperature synthesis, a new type of “double double perovskite” structure has been discovered in the family MnRMnSbO6 (R=La, Pr, Nd, Sm). This tetragonal structure has a 1:1 order of cations on both A and B sites, with A-site Mn2+ and R3+ cations ordered in columns and Mn2+ and Sb5+ having rock salt order on the B sites. The MnRMnSbO6 double double perovskites are ferrimagnetic at low temperatures with additional spin-reorientation transitions. The ordering direction of ferrimagnetic Mn spins in MnNdMnSbO6 changes from parallel to [001] below TC=76 K to perpendicular below the reorientation transition at 42 K at which Nd moments also order. Smaller rare earths lead to conventional monoclinic double perovskites (MnR)MnSbO6 for Eu and Gd
On the Origin of the Spontaneous Formation of Nanocavities in Hexagonal Bronzes (W,V)O3
[EN] Hexagonal (W,V)O3−x oxides of high thermal stability have been synthesized hydrothermally through the
intermediate products Nax(W,V)O3·zH2O and (NH4)0.33−x(W,V)O3−y. The obtained crystals show nanostructured
surface via the formation of a dense population of polyhedral nanocavities self-distributed
along particular crystallographic directions. Nanocavities present a regular size that ranges from 5 to
10 nm in both length and width. The synthesis process involves a significant topotactic relationship
between the as-synthesized product and the desired final product and this relationship is suggested as
the origin of the observed surface nanostructure. The comparison of our results with observations in
different solids has allowed us to suggest that the formation of nanocavities is an extensive spontaneous
process when materials are obtained by the chemical reactions of solids leading to products with defined
crystallographic orientation with respect to the original compound. The characterization provides evidence
regarding the potential relevance of nanocavities in the functional properties of the resulting solids.Authors acknowledge the financial support from DGICYT in Spain through projects MAT2010-19837-C06-05 and CTQ2012-37925-C03-1. Authors are also grateful to the Centro de Microscopia Electronica (UCM) for facilities.García-González, E.; Soriano Rodríguez, MD.; Urones-Garrote, E.; López Nieto, JM. (2014). On the Origin of the Spontaneous Formation of Nanocavities in Hexagonal Bronzes (W,V)O3. Dalton Transactions. 43:14644-14652. https://doi.org/10.1039/C4DT01465KS14644146524
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Ternary erbium chromium sulfides : structural relationships and magnetic properties
Single crystals of four erbium-chromium sulfides have been grown by chemical vapor transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er(3)CrS(6) octahedral sites are occupied exclusively by Cr(3+) cations, leading to one-dimensional CrS(4)(5-) chains of edge-sharing octahedra, while in Er(2)CrS(4), Er(3+), and Cr(2+) cations occupy the available octahedral sites in an ordered manner. By contrast, in Er(6)Cr(2)S(11) and Er(4)CrS(7), Er(3+) and Cr(2+) ions are disordered over the octahedral sites. In Er(2)CrS(4), Er(6)Cr(2)S(11), and Er(4)CrS(7), the network of octahedra generates an anionic framework constructed from M(2)S(5) slabs of varying thickness, linked by one-dimensional octahedral chains. This suggests that these three phases belong to a series in which the anionic framework may be described by the general formula [M(2n+1)S(4n+3)](x-), with charge balancing provided by Er(3+) cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er(4)CrS(7), Er(6)Cr(2)S(11), and Er(2)CrS(4) may thus be considered as the n = 1, 2, and infinity members of this series. While Er(4)CrS(7) is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er(3)CrS(6) (T(C)(Cr) = 30 K; T(C)(Er) = 11 K) and Er(2)CrS(4) (T(N)(Cr) = 42 K, T(N)(Er) = 10 K) whereas Er(6)Cr(2)S(11) exhibits ordering of the chromium sub-lattice only (T(N) = 11.4 K)
Halimium viscosum (Willk) P. Silva, Chemotype Celorico da Beira; the First Portuguese Chemotype
From Labdanes to Drimanes. Degradation of the Side Chain of Dihydrozamoranic Acid.
A new route for the degradation of the saturated side chain of dihydrozamoranic acid has been devised, giving an advanced intermediate, compound 14, useful for the synthesis of insect antifeedants such as warburganal and polygodial
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