| 1. |
- Nylén, Johanna, et al.
(författare)
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Structural behavior of the acetylide carbides Li2C2 and CaC2 at high pressure
- 2012
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 137:22, s. 224507-
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Tidskriftsartikel (refereegranskat)abstract
- The effects of high pressure (up to 30 GPa) on the structural properties of lithium and calcium carbide, Li2C2 and CaC2, were studied at room temperature by Raman spectroscopy in a diamond anvil cell. Both carbides consist of C2 dumbbells which are coordinated by metal atoms. At standard pressure and temperature two forms of CaC2 co-exist. Monoclinic CaC2-II is not stable at pressures above 2 GPa and tetragonal CaC2-I possibly undergoes a minor structural change between 10 and 12 GPa. Orthorhombic Li2C2 transforms to a new structure type at around 15 GPa. At pressures above 18 GPa (CaC2) and 25 GPa (Li2C2) Raman spectra become featureless, and remain featureless upon decompression which suggests an irreversible amorphization of the acetylide carbides. First principles calculations were used to analyze the pressure dependence of Raman mode frequencies and structural stability of Li2C2 and CaC2. A structure model for the high pressure phase of Li2C2 was searched by applying an evolutionary algorithm.
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| 2. |
- Ivarsson, Magnus, 1975-, et al.
(författare)
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A Fungal-Prokaryotic Consortium at the Basalt-Zeolite Interface in Subseafloor Igneous Crust
- 2015
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:10
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Tidskriftsartikel (refereegranskat)abstract
- We have after half a century of coordinated scientific drilling gained insight into Earth's largest microbial habitat, the subseafloor igneous crust, but still lack substantial understanding regarding its abundance, diversity and ecology. Here we describe a fossilized microbial consortium of prokaryotes and fungi at the basalt-zeolite interface of fractured subseafloor basalts from a depth of 240 m below seafloor (mbsf). The microbial consortium and its relationship with the surrounding physical environment are revealed by synchrotron-based X-ray tomographic microscopy (SRXTM), environmental scanning electron microscopy (ESEM), and Raman spectroscopy. The base of the consortium is represented by micro-stromatolites- remains of bacterial communities that oxidized reduced iron directly from the basalt. The microstromatolites and the surrounding basalt were overlaid by fungal cells and hyphae. The consortium was overgrown by hydrothermally formed zeolites but remained alive and active during this event. After its formation, fungal hyphae bored in the zeolite, producing millimetre-long tunnels through the mineral substrate. The dissolution could either serve to extract metals like Ca, Na and K essential for fungal growth and metabolism, or be a response to environmental stress owing to the mineral overgrowth. Our results show how microbial life may be maintained in a nutrient-poor and extreme environment by close ecological interplay and reveal an effective strategy for nutrient extraction from minerals. The prokaryotic portion of the consortium served as a carbon source for the eukaryotic portion. Such an approach may be a prerequisite for prokaryotic-eukaryotic colonisation of, and persistence in, subseafloor igneous crust.
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| 3. |
- Rodriguez Meizoso, Irene, et al.
(författare)
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In situ Raman spectroscopy for the evaluation of solubility in supercritical carbon dioxide mixtures
- 2012
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 65, s. 87-92
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Tidskriftsartikel (refereegranskat)abstract
- Solubility phenomena in supercritical carbon dioxide (SC-CO2) mixtures have been studied in situ using Raman spectroscopy. A Raman spectroscopy instrumentation has been linked to a high-pressure optical cell. The set-up was tested in the system SC-CO2/alkyl ketene dimer (AKD) under pressures up to 300 bars and temperatures up to 80 degrees C. As a proof of concept, the possibility to study solubility of AKD in SC-CO2 as well as solubility of SC-CO2 in AKD by studying the Raman signal of SC-CO2 has been presented. Statistically tested results show how these competitive phenomena depend on the density region of the SC-CO2. Raman spectra of AKD in the system AKD/SC-CO2 have also been acquired, demonstrating the prospect of quantitative analysis for solubility studies in SC-CO2. Furthermore, this versatile set-up provides information about thermal expansion of the vessel and evidences the need for corrected equations in this commonly used region of pressures and temperatures.
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| 4. |
- Weis, Franz A., et al.
(författare)
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Polarized IR and Raman spectra of zoisite : insights into OH-dipole orientation and the luminescence
- 2016
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Ingår i: European journal of mineralogy. - : Schweizerbart. - 0935-1221 .- 1617-4011. ; 38:3, s. 537-543
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Tidskriftsartikel (refereegranskat)abstract
- The OH-dipole in the mineral zoisite has been a topic of discussion regarding its general orientation and vibrational modes. We present new polarized single-crystal Raman and infrared spectra and verify the orientation of the OH-dipole along the crystallographic c axis with a slight deviation towards the crystallographic a axis. Polarized Raman and FTIR spectra confirm that the OH band at 3150 cm(-1) corresponds to the O(10)-H center dot center dot center dot O(4) hydrogen bridge and exclude a previously suggested second hydrogen bridge O(10)-H center dot center dot center dot O(2). Further, Raman spectra provide insights on the luminescence of zoisite and the interference of luminescence peaks in the OH-region.
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| 5. |
- Manoun, B., et al.
(författare)
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High temperature induced phase transitions in Sr2ZnWO6 and Sr2CoWO6 double perovskite oxides : Raman spectroscopy as a tool
- 2012
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1029, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report high-temperature (up to 550 °C) Raman spectroscopy of phase transitions in Sr2MWO6 (M = Zn, Co) double perovskite oxides. For Sr2ZnWO6 modes centered at 137 cm−1, 152 cm−1, merge around 80 °C. The same behavior was observed for the 436 cm−1 and 447 cm−1 modes. The mode centered at 854 cm−1 shows a change in the slope at the same temperature, thus indicating a first order phase transition from the monoclinic (P21/n) to tetragonal (I4/m) structure. With increasing temperature, a little change in the slope of the temperature dependence of mode centered at 855 cm−1 is observed around 480 °C which might be a sign of the second phase transition in Sr2ZnWO6 (tetragonal (I4/m) to cubic (Fm-3m)). The temperature dependence of the full width at half maximum (FWHM) of the most intense modes in Sr2ZnWO6 spectra was studied. The width behaves linearly as a function of temperature with a break observed in the slope of the width of the modes at 80 °C; thus, showing the first phase transition occurrence. For Sr2CoWO6 the transition from tetragonal (I4/m) structure to cubic (Fm-3m) phase is accompanied by considerable changes in the temperature dependence of modes centered at 438 cm−1 and 845 cm−1. The transition was observed around 420 °C.
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| 6. |
- Shebanova, Olga
(författare)
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The High-Pressure Study on the Fe - O System: Thermodynamics and Phase Transitions of Iron Ferrite (FeFe2O4)
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge about the stability of phases and their relationships in the Fe-O system at high pressures and temperatures is essential in implications of the multifarious states of iron oxides for models of the evolution of the Earth. In this respect, the iron ferrite magnetite (FeFe2O4) plays a significant role since it participates in the control of geochemistry of ferric iron, and hence oxygen fugacity in the Earth`s deep interior.High-pressure experiments on Fe3O4 were performed using the diamond anvil cell technique combined with the laser and electrical resistive heating. The approach based on the combination of the synchrotron x-ray diffraction with Raman spectroscopic measurements benefited from the complementarity of the two methods originating from the different sensitivity to a range of structural order. High-pressure transformation of magnetite to a dense polymorph of the CaTi2O4-type structure proceeds via an intermediate step of the decomposition into a mixture of oxides on a microscopic scale. The kinetic hindrance of the reaction of the decomposition effectively prevents a phase separation controlled by diffusion and restricts the formation of the daughter products to locally ordered structures in the strained lattice of magnetite.Thermodynamic analysis of the observed phase transformations along with published results on the elastic properties and pressure-induced transitions of iron oxides has led to the reassessment of the phase diagram of Fe3O4. The pressure - temperature field of its stability with respect to the breakdown to a mixture of oxides FeO and Fe2O3, and to the transition to a high-pressure form, has been accordingly modified.
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| 7. |
- Mirinioui, F., et al.
(författare)
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Sequence of phase transitions induced by chemical composition and high temperature in [Ba2CaWO6]((1-x))[Sr2CaWO6](x) double perovskite tungsten oxides
- 2015
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 232, s. 182-192
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Tidskriftsartikel (refereegranskat)abstract
- [Ba2CaWO6](1-x)[Sr2CaWO6](x) (0 <= x <= 1) materials were synthesized by the high temperature solid state reaction and firing methods, and characterized using techniques of X-ray diffraction and Raman spectroscopy. The crystal structures were determined by Rietveld refinements on the laboratory X-ray powder diffraction data. As a function of composition, upon increasing the strontium content, the samples exhibit a sequence of three phase transitions: from cubic (Fm (3) over barm) to tetragonal (I4/m) to monoclinic structural phases (I2/m, P2(1)/n). These transitions have been confirmed by Raman studies Fm (3) over barm(x=0) -> I4/m(0.1 <= x <= 0.2) -> I2/m(0.3 <= x <= 0.5) -> P2(1)/n(0.6 <= x <= 1) Furthermore, increasing the temperature for the compositions [Ba2CaWO6](1-x)[Sr2CaWO6](x) (0.1 <= x < 1), manifests the P2(1)/n to I2/m, the I2/m to I4/m and the I4/m to Fm<(3)over bar>m phase transitions. For the compositions (0.1 <= x <= 0.2) the tetragonal to cubic phase transition is well illustrated. For the room temperature I2/m monoclinic compositions, two phase transitions were observed for all the compositions with x ranging from 0.3 to 0.5: from the monoclinic (I2/m) to tetragonal (I4/m), and from I4/m to Fm (3) over barm structures. Finally, for the room temperature P2(1)/n monoclinic compositions, only two phase transitions are observed in the temperature range probed by Raman spectroscopy, the temperature was not high enough to reach the tetragonal-to-cubic phase transition.
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| 8. |
- Manoun, B., et al.
(författare)
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High temperature and composition induced phase transitions in LiZnV1-xAsxO4 phenacites : Crystal structure and Raman spectroscopy studies
- 2015
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 151, s. 956-964
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Tidskriftsartikel (refereegranskat)abstract
- In this work, using techniques of X-ray diffraction and Raman spectroscopy, we report the composition and high-temperature induced phase transition in the system LiZnV1-xAsxO4 (0 <= x <= 1). Both techniques showed that the increase of arsenic amount induced a structural transition from R-3 LiZnVO4 type to LiZnAsO4 type belonging to R3 space group, the transition occurring between x = 0.7 and x = 0.8. Furthermore, increasing temperature for the compositions (0.8 <= x <= 1) manifests a transition from the LiZnAsO4 structural type with R3 space group to the R-3 LiZnVO4 structural type. For this series, the transition from the space group R3 to the centro-symmetric space group R-3 shows considerable changes in the compositional and temperature dependencies of the bands: spectral positions of all the observed Raman bands exhibit shifts linearly proportional to the temperature increase, with points of shift-rate changes revealing a symmetry change. The Raman-spectra based temperature-composition phase diagram confirms the results obtained using the method of Rietveld refinements, thus showing the R-3 to R3 transition occurring between x = 0.7 and 0.8.
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| 9. |
- Tamraoui, Y., et al.
(författare)
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X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2-xSrxMgTeO6 (0 <= x <= 2)
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 603, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction and Raman spectroscopy studies of Sr-substituted double perovskite compounds Ba2-xSrxMgTeO6 with (0 <= x <= 2) were carried out. At room temperature, both Rietveld refinements and Raman studies showed that two phase transitions occurred as a function of increased strontium content; from cubic to tetragonal structure, at x similar to 1.5(1), and from the tetragonal to monoclinic structure at x similar to 1.9(1). Furthermore, upon temperature increase up to 430 degrees C, the monoclinic and tetragonal perovskites manifest transformations to the tetragonal and cubic symmetries, and to the cubic symmetry, respectively. For this series, the transitions show considerable changes in the compositional and temperature dependencies of the modes, the spectral positions of which exhibit a linear behavior. The symmetry transformations between the encountered three crystal systems is revealed by significant changes of the slopes. (C) 2014 Elsevier B. V. All rights reserved.
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| 10. |
- Bensaid, H., et al.
(författare)
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New molybdate Li2Co2xNix(MoO 4) 3 (0≤x≤2) materials with a lyonsite structure: X-ray diffraction and Raman spectroscopy studies
- 2013
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Ingår i: Journal of Molecular Structure. - : Elsevier. - 0022-2860 .- 1872-8014. ; 1031, s. 152-159
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Tidskriftsartikel (refereegranskat)abstract
- A solid solution was found to exist in the quaternary Li2O–CoO–NiO–MoO3 system between the two phases Li2Co2(MoO4)3 and Li2Ni2(MoO4)3. Both Li2Co2(MoO4)3 and Li2Ni2(MoO4)3 are isostructural with the mineral lyonsite, and substitution according to the formula Li2Co2−xNix(MoO4)3 (0 ⩽ x ⩽ 2) demonstrates that a complete solid solution exits. Rietveld analysis revealed that solid solution crystallizes at room temperature in orthorhombic space group Pnma (D2h). The structure shows that if the corners and edges octahedra share in the leaves, they share faces columns. Nickel and cobalt are shared statically in the trigonal prism and octahedral sites. The results of these compositions are consistent with studies where the Raman spectra. Therefore, all compositions are similar and show linear changes frequencies depending on the composition due to the substitution of Co2+ by Ni2+ with a larger radius.
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