15,312 research outputs found
Characterisation and textural analysis of Middle Bronze Age Transdanubian inlaid wares of the Encrusted Pottery Culture, Hungary: a preliminary study
Inlaid ceramics belonging to the Encrusted Pottery Culture and dated to the Middle Bronze Age (2000–1500 BC) are highly distinctive vessels with complex decorative motifs found in large numbers in the Transdanubia region of Hungary. Despite this considerable corpus of material there has been little systematic investigation of the composition of the inlays. Micro-analysis of Transdanubian inlaid wares by X-ray diffraction (XRD), micro-Fourier transform infrared microscopy (FT-IR), and scanning electron microscopy (SEM) provides new compositional, structural and textural information on the inlays. In contrast to common statements in the literature regarding the materials used to make inlays, these new data show that the majority of inlays are composed of hydroxyapatite (bone) that was previously ashed, although some of the inlays are composed of calcium carbonate. Additional compositional and textural variation in the bone inlays suggests that bone material from different skeletal elements and/or of different age may have been used, and that contrasting recipes for inlay preparation were employed during fabrication. These results suggest that the production of inlaid vessels of the Encrusted Pottery Culture was more complex than has hitherto been thought
Charge Transfer Induced Molecular Hole Doping into Thin Film of Metal-Organic-Frameworks
Despite the highly porous nature with significantly large surface area, metal
organic frameworks (MOFs) can be hardly used in electronic, and optoelectronic
devices due to their extremely poor electrical conductivity. Therefore, the
study of MOF thin films that require electron transport or conductivity in
combination with the everlasting porosity is highly desirable. In the present
work, thin films of Co3(NDC)3DMF4 MOFs with improved electronic conductivity
are synthesized using layer-by-layer and doctor blade coating techniques
followed by iodine doping. The as-prepared and doped films are characterized
using FE-SEM, EDX, UV/Visible spectroscopy, XPS, current-voltage measurement,
photoluminescence spectroscopy, cyclic voltammetry, and incident photon to
current efficiency measurements. In addition, the electronic and semiconductor
property of the MOF films are characterized using Hall Effect measurement,
which reveals that in contrast to the insulator behavior of the as-prepared
MOFs, the iodine doped MOFs behave as a p-type semiconductor. This is caused by
charge transfer induced hole doping into the frameworks. The observed charge
transfer induced hole doping phenomenon is also confirmed by calculating the
densities of states of the as-prepared and iodine doped MOFs based on density
functional theory. Photoluminescence spectroscopy demonstrate an efficient
interfacial charge transfer between TiO2 and iodine doped MOFs, which can be
applied to harvest solar radiations.Comment: Main paper (19 pages, 6 figures) and supplementary information (15
pages, 10 figures), accepted in ACS Appl. Materials & Interface
Tetrahedrally coordinated carbonates in Earth's lower mantle
Carbonates are the main species that bring carbon deep into our planet
through subduction. They are an important rock-forming mineral group,
fundamentally distinct from silicates in Earth's crust in that carbon binds to
three oxygen atoms, while silicon is bonded to four oxygens. Here, we present
experimental evidence that under the sufficiently high pressures and high
temperatures existing in the lower mantle, ferromagnesian carbonates transform
to a phase with tetrahedrally coordinated carbons. Above 80 GPa, in situ
synchrotron infrared experiments show the unequivocal spectroscopic signature
of the high-pressure phase of (Mg,Fe)CO. Using ab-initio calculations, we
assign the new IR signature to C-O bands associated with tetrahedrally
coordinated carbon with asymmetric C-O bonds. Tetrahedrally coordinated
carbonates are expected to exhibit substantially different reactivity than low
pressure three-fold coordinated carbonates, as well as different chemical
properties in the liquid state. Hence this may have significant implications on
carbon reservoirs and fluxes and the global geodynamic carbon cycle
Lattice structure and magnetization of LaCoO3 thin films
We investigate the structure and magnetic properties of thin films of the
LaCoO compound. Thin films are deposited by pulsed laser deposition on
various substrates in order to tune the strain from compressive to tensile.
Single-phase (001) oriented LaCoO layers were grown on all substrates
despite large misfits. The tetragonal distortion of the films covers a wide
range from -2% to 2.8%. Our LaCoO films are ferromagnetic with Curie
temperature around 85 K, contrary to the bulk. The total magnetic moment is
below /Co, a value relatively small for an exited spin-state
of the Co ions, but comparable to values reported in literature. A
correlation of strain states and magnetic moment of Co ions in
LaCoO thin films is observed.Comment: submitted tu European Phys. J.
Nomenclature of the hydrotalcite supergroup: Natural layered double hydroxides
Layered double hydroxide (LDH) compounds are characterized by structures in which layers with a brucite-like structure carry a net positive charge, usually due to the partial substitution of trivalent octahedrally coordinated cations for divalent cations, giving a general layer formula [( M 2+ 1-x M 3+ x )(OH)2] x +. This positive charge is balanced by anions which are intercalated between the layers. Intercalated molecular water typically provides hydrogen bonding between the brucite layers. In addition to synthetic compounds, some of which have significant industrial applications, more than 40 mineral species conform to this description. Hydrotalcite, Mg6Al2(OH) 16[CO3]•4H2O, as the longest-known example, is the archetype of this supergroup of minerals. We review the history, chemistry, crystal structure, polytypic variation and status of all hydrotalcite-supergroup species reported to date. The dominant divalent cations, M 2+, that have been reported in hydrotalcite supergroup minerals are Mg, Ca, Mn, Fe, Ni, Cu and Zn; the dominant trivalent cations, M 3+, are Al, Mn, Fe, Co and Ni. The most common intercalated anions are (CO3)2-, (SO4)2- and Cl -; and OH-, S2- and [Sb(OH)6] - have also been reported. Some species contain intercalated cationic or neutral complexes such as [Na(H2O)6]+ or [MgSO4]0. We define eight groups within the supergroup on the basis of a combination of criteria. These are (1) the hydrotalcite group, with M 2+:M 3+ = 3:1 (layer spacing ∼7.8 Å); (2) the quintinite group, with M 2+:M 3+ = 2:1 (layer spacing ∼7.8 Å); (3) the fougèrite group, with M 2+ = Fe2+, M 3+ = Fe3+ in a range of ratios, and with O2- replacing OH- in the brucite module to maintain charge balance (layer spacing ∼7.8 Å); (4) the woodwardite group, with variable M 2+:M 3+ and interlayer [SO4] 2-, leading to an expanded layer spacing of ∼8.9 Å; (5) the cualstibite group, with interlayer [Sb(OH)6]- and a layer spacing of ∼9.7 Å; (6) the glaucocerinite group, with interlayer [SO4]2- as in the woodwardite group, and with additional interlayer H2O molecules that further expand the layer spacing to ∼11 Å; (7) the wermlandite group, with a layer spacing of ∼11 Å, in which cationic complexes occur with anions between the brucite-like layers; and (8) the hydrocalumite group, with M 2+ = Ca2+ and M 3+ = Al, which contains brucite-like layers in which the Ca:Al ratio is 2:1 and the large cation, Ca2+, is coordinated to a seventh ligand of 'interlayer' water. The principal mineral status changes are as follows. (1) The names manasseite, sjögrenite and barbertonite are discredited; these minerals are the 2H polytypes of hydrotalcite, pyroaurite and stichtite, respectively. Cyanophyllite is discredited as it is the 1M polytype of cualstibite. (2) The mineral formerly described as fougèrite has been found to be an intimate intergrowth of two phases with distinct Fe 2+:Fe3+ ratios. The phase with Fe2+:Fe 3+ = 2:1 retains the name fougèrite; that with Fe 2+:Fe3+ = 1:2 is defined as the new species trébeurdenite. (3) The new minerals omsite (IMA2012-025), Ni 2Fe3+(OH)6[Sb(OH)6], and mössbauerite (IMA2012-049), Fe3+ 6O 4(OH)8[CO3]•3H2O, which are both in the hydrotalcite supergroup are included in the discussion. (4) Jamborite, carrboydite, zincaluminite, motukoreaite, natroglaucocerinite, brugnatellite and muskoxite are identified as questionable species which need further investigation in order to verify their structure and composition. (5) The ranges of compositions currently ascribed to motukoreaite and muskoxite may each represent more than one species. The same applies to the approved species hydrowoodwardite and hydrocalumite. (6) Several unnamed minerals have been reported which are likely to represent additional species within the supergroup. This report has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association, voting proposal 12-B. We also propose a compact notation for identifying synthetic LDH phases, for use by chemists as a preferred alternative to the current widespread misuse of mineral names. © 2012 Mineralogical Society.Fil: Mills, S.J.. Museum Victoria; AustraliaFil: Christy, A.G.. Australian National University. Centre for Advanced Microscopy; AustraliaFil: Génin, J. M. R.. CNRS-Université de Lorraine; FranciaFil: Kameda, T.. Tohoku University. Graduate School of Environmental Studies; JapónFil: Colombo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin
59Co NMR study of the Co states in superconducting and anhydrous cobaltates
Co NMR spectra in oriented powders of NaCoO and in its
hydrated superconducting phase (HSC) NaCoO,1.3HO reveal a
single electronic Co state with identical independent NMR shift tensor.
These phases differ markedly from NaCoO, in which we resolve 3
types of Co sites. The large T variation of their spin susceptibilities and the anisotropy of the orbital susceptibility allow us
to conclude that charge disproportionation occurs, in a non magnetic Co
and two magnetic sites with about 0.3 and 0.7 holes in the multiplet.
The data are consistent with those for the single Co site in the anhydrous and
HSC phase assuming the expected Co charge.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
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