Luo C.W.,National Chiao Tung University |
Wu I.H.,National Chiao Tung University |
Cheng P.C.,National Chiao Tung University |
Lin J.-Y.,National Chiao Tung University |
And 12 more authors.
New Journal of Physics | Year: 2012
The ultrafast quasiparticle dynamics of Fe1+ySe 1-xTex single crystals were investigated by dual-color transient reflectivity measurements (ΔR/R) from 4.3 to 290 K. The electron-phonon coupling strength λ (= 0.16-0.01) and the temperature-dependent energy of longitudinal-acoustic phonons were, respectively, obtained from the relaxation time of a fast component and the period of an oscillation component in ΔR/R. Such a small λ demonstrates the unconventional origin of superconductivity in FeSe. Moreover, the temperature-dependent ΔR/R exhibits anomalous changes at T c, 90 K and 230 K, unambiguously revealing the phase transition as well as the phonon softening via the magnetoelastic effect. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Ovkun A.B.,Moscow State University |
Indi L.B.,CNR Institute of Geosciences and Earth Resources |
Aranin V.G.,Fersman Mineralogical Museum |
Itvin Y.L.,Institute of Experimental Mineralogy
Mineralogical Magazine | Year: 2013
Kudryavtsevaite, ideally Na3MgFe3+Ti 4O12, is a new mineral from kimberlitic rocks of the Orapa area, Botswana. It occurs as rare prismatic crystals, up to 100 mm across, associated with Mg-rich ilmenite, freudenbergite and ulvospinel. Kudryavtsevaite is opaque with a vitreous lustre and shows a black streak. It is brittle; the Vickers hardness (VHN100) is 901 kg mm-2 (range: 876-925) (Mohs hardness ∼6). In reflected light, kudryavtsevaite is moderately bireflectant and very weakly pleochroic from dark grey to a slightly bluish grey. Under crossed polars, it is very weakly anisotropic with greyish-bluish rotation tints. Internal reflections are absent. Reflectance values (%), Rmin and Rmax, are: 21.3, 25.4 (471.1 nm), 20.6, 24.1 (548.3 nm), 20.0, 23.5 (586.6 nm) and 19.1, 22.4 (652.3 nm). Kudryavtsevaite is orthorhombic, space group Pnma, with a = 27.714(1), b = 2.9881(3), c = 11.3564(6) Å, V= 940.5(1) Å3, and Z= 4. The crystal structure [R1 = 0.0168 for 819 reflections with I> 2σ(I)] consists of edge-sharing and corner-sharing chains composed of Mg, Fe3+ and Ti atoms coordinated by six atoms of oxygen and running along the b axis, with Na filling the tunnels formed by the chains. The eight strongest powder-diffraction lines [d in Å (I/I0) (hkl)] are: 7.17 (100) (301), 4.84 (70) (302), 2.973 (35) (901), 2.841 (50) (004), 2.706 (50) (902), 2.541 (50) (312), 2.450 (70) (611), and 2.296 (45) (612). The average results of 12 electron microprobe analyses gave (wt.%): Na2O 16.46(15), CaO 1.01(3), MgO 5.31(5), Fe2O3 22.24(32), Cr2O3 1.05(6), Al2O3 0.03(2), TiO2 53.81(50), total 99.91, corresponding to the empirical formula (Na2.89Ca0.10) Σ2.99(Ti3.67Fe3+ 1.52Mg 0.72Cr0.08)Σ, or ideally Na3MgFe 3+Ti4O12. The new mineral has been approved by the IMA-CNMNC and named for Galina Kudryavtseva (1947-2006), a well known Russian mineralogist and founder of the Diamond Mineralogy Laboratory and scientific school for investigation of diamond mineralogy and geochemistry at the Lomonosov State University in Moscow, Russia. © 2013 The Mineralogical Society.
Lin J.-Y.,National Chiao Tung University |
Hsieh Y.S.,National Chiao Tung University |
Chareev D.A.,Institute of Experimental Mineralogy |
Vasiliev A.N.,Moscow State University |
And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011
The comprehensive low-temperature specific-heat C(T) data identify both an isotropic s-wave and extended s-wave order parameters coexisting in a superconducting single-crystal FeSe with T c = 8.11 K. The isotropic gap Δ 0 = 1.33 meV on the hole Fermi sheets and the extended s-wave gap Δ = Δ e(1+αcos2) with Δ e = 1.13 meV and α = 0.78 on the electron Fermi sheets. The extended s wave is rather anisotropic, but the low-energy quasiparticle excitations demonstrate no sign of the accidental nodes. The coefficient γ(H) manifesting the quasiparticle contribution to C is a nonlinear function of the applied magnetic field H in the mixed state in accord with the anisotropic multiorder parameters. © 2011 American Physical Society.
Bindi L.,CNR Institute of Geosciences and Earth Resources |
Dymshits A.M.,Moscow State University |
Bobrov A.V.,Moscow State University |
Litasov K.D.,Tohoku University |
And 5 more authors.
American Mineralogist | Year: 2011
The crystal structure and chemical composition of a crystal of Na 2MgSi5O12 garnet synthesized in the model system Mg3Al2Si3O12-Na 2MgSi5O12 at 17.5 GPa and 1700 °C have been investigated. Quantitative analysis leads to the following formula: Na 1.98Mg1.00Si5.01O12. Na 2MgSi5O12 garnet was found to be tetragonal, space group I41/acd, with lattice parameters a = 11.3966(6), c = 11.3369(5) Å, V = 1472.5(1) Å3. The structure was refined to R = 5.13% using 771 independent reflections. Sodium and Mg are disordered at the X sites (with a mean bond distance of 2.308 Å for both the sites), whereas Si is ordered at both the Y (mean: 1.793 Å) and Z sites (means: 1.630 and 1.624 Å). Na-bearing majoritic garnet may be an important potential sodium concentrator in the lower parts of the upper mantle and transition zone. The successful synthesis of the Na2MgSi 5O12 end-member and its structural characterization is of key importance because the study of its thermodynamic constants combined with the data of computer modeling provides new constraints on thermobarometry of majorite garnet assemblages.
Pekov I.V.,Moscow Stale University |
Olysych L.V.,Moscow Stale University |
Chukanov N.V.,RAS Institute of Problems of Chemical Physics |
Zubkova N.V.,Moscow Stale University |
And 4 more authors.
Canadian Mineralogist | Year: 2011
Chemical and structural variations of 11 minerals of the cancrinite group having an Al,Si,O framework of the AB type are summarized and discussed. The total number of chemically studied samples is 360 (our data and literature data): cancrinite 192 and 35, vishnevite 21 and 13, cancrisilite 19 and 10, kyanoxalite and oxalate-rich intermediate members of the cancrinite- kyanoxalite series 12 and 0, davyne 10 and 23, depmeierite 2 and 0, balliranoite 1 and 0, hydroxycancrinite 0 and 1, quadridavyne 0 and 10, microsommite 0 and 8, and pitiglianoite 0 and 3. We provide original structural data for nine samples of distinct varieties of cancrinite and one sample of cancrisilite, as well as published structural data on the above-listed minerals. The major topics are the distribution and ratios of extra-framework components, cations (Na +, Ca 2+, K +), anions (CO 3 2-, SO 4 2-, Cl -, C 2O 4 2-, PO 4 3-) and H 2O, with special emphasis on oxalate and phosphate anions. The idealized formula of cancrinite has been refined: Na 7Ca[Al 6Si 6O 24](CO 3) 1.5·2H 2O. The solid-solution series with coupled substitutions in the framework and extra-framework portions are discussed, as is the genetic aspect of crystal chemistry of cancrinite-group minerals with a AB-type framework.
Shchipansky A.A.,Russian Academy of Sciences |
Khodorevskaya L.I.,Institute of Experimental Mineralogy |
Konilov A.N.,Russian Academy of Sciences |
Slabunov A.I.,Russian Academy of Sciences
Russian Geology and Geophysics | Year: 2012
The paper focuses on the metamorphic geology of the oldest crustal eclogites discovered in the Late Archean tonalite-trondhjemite-granodiorite (TTG) complex of the Belomorian Mobile Belt on the Kola Peninsula. Eclogite bodies are, most likely, widespread. We studied one of the key objects, the Kuru-Vaara quarry, where several tens of retrogressed eclogite blocks randomly embedded in the TTG gneisses were stripped at the benches. Based on the field observations, two visually different types of eclogites have been recognized: "southern", strongly retrogressed coarse-grained, and "northern", well-preserved fine-grained. The southern eclogite blocks bear evidence of their partial melting with the formation of veins and melt percolation channels. The northern eclogite blocks show no evidence of melting. Despite the significant mineralogic difference, both types of eclogites can be assigned to amphibole eclogite facies. The applied jadeite solubility geobarometers yielded the minimum pressures of ~12 kbar for the northern eclogites and ~14-14.5 kbar for the southern ones. The used geothermometers yielded ~700*deg;C and ~750*deg;C, respectively. But the presence of quartz lamellae in Na-clinopyroxenes in both types of eclogites and their bulk compositions corresponding to high-Mg basalts suggest that the Kuru-Vaara eclogites might have reached the field of ultrahigh-pressure metamorphism. Analysis of the tentative P-T paths of metamorphic evolution for both types of eclogites showed that their burial-exhumation cycle might have taken as short as a few million years. The set of presented data suggests that the formation of the Kuru-Vaara eclogites was related to the subduction of the Archean oceanic crust, which should have differed in composition and structure from the modern oceanic crust. © 2011.
Taran Y.,National Autonomous University of Mexico |
Zelenski M.,Institute of Experimental Mineralogy
Geological Society Special Publication | Year: 2015
In this review paper a set of chemical (H2O, CO2, S, HCl, HF) and water isotopic (δD, δ18O) data is compiled for 26 subduction zone volcanoes and 3 volcanoes of other tectonic settings. To the arc-volcano dataset we added new data on high-temperature gas vents from three Kamchatkan volcanoes (Gorely, Bezymianny and Tolbachik) and also published data on the chemical composition of volcanic plumes obtained by remote instrumental techniques (Open-Path Fourier Transform Infrared Spectroscopy (OP-FTIR), Differential Optical Absorption Spectroscopy (DOAS) MultiGas) for volcanoes of different tectonic settings. Three typical cases of the persistent volcanic degassing in terms of δD, δ18O of the volcanic vapour and its HCl content are discussed in detail: (1) Kudryavy type with a clear two-end-member mixing behaviour; (2) degassing of active or cooling lava domes with fractionation of both water isotopes and Cl content; and (3) degassing of small volcanic islands with a complex admixing of meteorics and seawater. We show that independently of the complexity of the shallow processes which affect volcano degassing, the highest temperature volcanic gases are characterized by δD values and HCl concentrations close to 225% V-SMOW and 0.5-1.0 mol%, respectively. These values are the same for any volcanic arc (except maybe Mediterranean volcanoes) and are the result of seawater recycling at subduction zones on the global scale. In contrast to volcanic fluids of nonarc settings, the arc-magmatic fluid has uniformity not only in water isotopic composition and Cl content but also in the total composition (H-C-O-S-Cl-F). © 2015 The Geological Society of London.
Gnezdilov V.,TU Braunschweig |
Gnezdilov V.,Ukrainian Academy of Sciences |
Pashkevich Y.G.,TU Braunschweig |
Pashkevich Y.G.,Ukrainian Academy of Sciences |
And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013
Polarized Raman-scattering spectra of superconducting, single-crystalline FeSe evidence pronounced phonon anomalies with temperature reduction. A large (∼6.5%) hardening of the B1g(Fe) phonon mode is attributed to the suppression of local fluctuations of the iron spin state with a gradual decrease of the iron paramagnetic moment. Ab initio lattice dynamic calculations support this conclusion. The enhancement of the low-frequency spectral weight above the structural phase transition temperature Ts and its change below Ts is discussed in relation with the opening of an energy gap between low (S=0) and higher spin states which prevents magnetic order in FeSe. The very narrow phonon linewidths compared to observations in FeTe suggest the absence of intermediate spin states in the fluctuating spin state manifold in FeSe. In the tetragonal phase under approaching Ts we observe the development of a quasielastic Raman response that is typical for the presence of nematic fluctuations. © 2013 American Physical Society.
Lakshtanov L.Z.,Copenhagen University |
Lakshtanov L.Z.,Institute of Experimental Mineralogy |
Bovet N.,Copenhagen University |
Stipp S.L.S.,Copenhagen University
Geochimica et Cosmochimica Acta | Year: 2011
The kinetics of calcite precipitation in the presence of alginate was investigated using the constant composition technique. In the concentration range investigated (0.0002-0.005gL-1), alginate inhibits calcite precipitation. The extent of inhibition increased with increased alginate concentration and decreased solution supersaturation. Alginate adsorption, derived from normalized calcite precipitation rates, is described satisfactorily by the Langmuir adsorption model. At lowest supersaturation, alginate adsorption onto calcite probably reaches its maximal uptake of 7.5E-4gm-2, corresponding to surface coverage of one molecule for each 200-300nm2, depending on the molecular mass of alginate. This means that one alginate molecule can be bound over 100-150 Ca surface sites. Initially, on the surface of the inhibited calcite, XPS identified alginate but after further time in solution, when the system had recovered, XPS demonstrated that it disappeared from the surface, presumably buried under the newly formed calcite. The alginate affinity constant decreases with increasing supersaturation, evidence for incomplete adsorption. A simple model based on competition between growth and desorption effectively describes the observed change in the adsorption constant. © 2011 Elsevier Ltd.
Zelenski M.,Institute of Experimental Mineralogy |
Taran Y.,National Autonomous University of Mexico
Bulletin of Volcanology | Year: 2011
We report chemical compositions (major and trace components including light hydrocarbons), hydrogen, oxygen, helium and nitrogen isotope ratios of volcanic and geothermal fluids of Mutnovsky volcano, Kamchatka. Several aspects of the geochemistry of fluids are discussed: chemical equilibria, mixing of fluids from different sources, evaluation of the parent magmatic gas composition and contributions to magmatic vapors of fluids from different reservoirs of the Kamchatkan subduction zone. Among reactive species, hydrogen and carbon monoxide in volcanic vapors are chemically equilibrated at temperatures <300°C with the SO2-H2S redox-pair. A metastable equilibrium between saturated and unsaturated light hydrocarbons is attained at close to discharge temperatures. Methane is disequilibrated. Three different sources of fluids from three fumarolic fields in the Mutnovsky craters can be distinguished: (1) magmatic gas from a large convecting magma body discharging through Active Funnel, a young crater with the hottest fumaroles (up to 620°C) contributing ~80% to the total volcanic gas output; (2) volcanic fluid from a separate shallow magma body beneath the Bottom Field of the main crater (96-280°C fumaroles); and (3) hydrothermal fluid with a high relative and absolute concentrations of CH4 from the Upper Field in the main crater (96-285°C fumaroles). The composition of the parent magmatic gas is estimated using water isotopes and correlations between He and other components in the Active Funnel gases. The He-Ar-N2 systematics of volcanic and hydrothermal fluids of Mutnovsky are consistent with a large slab-derived sedimentary nitrogen input for the nitrogen inventory, and we calculate that only ~1% of the magmatic N2 has a mantle origin and <<1% is derived from the arc crust. © 2011 Springer-Verlag.