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| 2. |
- Hudl, Matthias, et al.
(författare)
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Investigation of the magnetic phase transition and magnetocaloric properties of the Mn2FeSbO6 ilmenite
- 2013
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 331, s. 193-197
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic phase transition and magnetocaloric properties of both mineral and synthetic melanostibite Mn2FeSbO6 with ilmenite-type structure have been studied. Mn2FeSbO6 orders ferrimagnetically below 270 K and is found to undergo a second-order magnetic phase transition. The associated magnetic entropy change was found to be 1.7 J/kg K for the mineral and 1.8 J/kg K for the synthetic melanostibite for 5 T field change. For the synthetic Mn2FeSbO6 the adiabatic temperature change was estimated from magnetic- and specific heat measurements and amounts to 0.2 K in 1 T field change. Perspectives of the functional properties of Mn2FeSbO6-based materials are discussed.
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| 6. |
- Azdouz, M, et al.
(författare)
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Synthesis, Rietveld refinements and Raman spectroscopy studies of the solid solution Na1-xKxPb4(VO4)(3) (0 <= x <= 1)
- 2010
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 963:2-3, s. 258-266
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Tidskriftsartikel (refereegranskat)abstract
- In the present study we report the synthesis, crystal structure and Raman spectroscopy studies of Na1-xKxPb4(VO4)(3) orthovanaclates solid solutions (0 <= x <= 1). Rielveld refinements showed that this solid solution is continuous adopting P6(3)/m (no. 176) space group. Some of Pb(II) cations are located in the (6 h) sites. The ninefold coordination sites (4f) are equally occupied by the other lead cations and the K+ and Na+ monovalent ions. The structure can be described as built up from [VO4](3-) tetrahedral and Ph2+ of sixfold coordination cavities (6 h positions), which delimit void hexagonal tunnels running along [0 0 1]. These tunnels are connected by cations of mixed sites (4f) half occupied by Pb(II) and half by Na+/K+ mixed cations. The existence of this type of lacunar apatite seems to be conditioned by the presence of lone pair cations Pb(II). Raman spectra of all the compositions are similar and show some linear shifts in band positions as a function of the composition toward high values due the substitutions of Na+ by K+ with a larger radius. No considerable changes in the temperature dependence of the Raman modes and the corresponding FWHM are observed and thus no temperature induced phase transition is observed in Na0.5K0.5Pb4(VO4)(3) up to 650 K.
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| 7. |
- 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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| 8. |
- Bensaid, H., et al.
(författare)
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X-ray structure refinement of solid solution Ba2.15-xNa0.7+xNb5-xWxO15 and the investigation of the orthorhombic-tetragonal phase transition by Raman spectroscopy
- 2011
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 988:1-3, s. 136-143
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Tidskriftsartikel (refereegranskat)abstract
- Crystal structures of Ba2.15-xNa0.7+xNb5-xWxO15 (BaNaNbW) materials were investigated by X-ray diffraction and refined using the Rietveld method. It is shown that all the samples crystallize in the tungsten tetragonal bronze (TTB) like structure and form a solid solution in the range (0 ≤ x ≤ 1). To study the temperature induced phase transition in these compounds, Raman spectra were collected in situ at room pressure and elevated temperatures, up to 330°. The Raman results show strong evidence that the materials under study go through a phase transition around Te = 270 °C. The value of the transition temperature depends on the chemical composition and increases with increasing tungsten content in the materials at a linear rate. The observation of this phase transition by Raman technique is in agreement with dielectric spectroscopy anomaly.
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| 9. |
- Bih, H., et al.
(författare)
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Electrical Transport Properties Of Iodine Oxide Phosphate Glasses Issued From The NaI-Li2O-WO3-P2O5 System
- 2010
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Ingår i: Moroccan Journal of Condensed Matter. - 1114-2073. ; 12, s. 98-102
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: This work concerns the investigation of ion transport behaviour of NaI containing lithium tungstenphosphate glasses in order to understand better the role of NaI in the ionic cation transport. Glasses obtained in thesystem 0.5[x(2NaI)-(1-x)Li2O]-0.5[0.25(WO3)2-0.75P2O5] were investigated. The glass samples have beencharacterised using powder X-ray diffraction (XRD), thermal analysis, density and impedance spectroscopy. X-raydiffraction and thermal studies have confirmed that these glasses can be formed in the range x = 0 to 1. The mixedalkali glasses have shown higher activation energies and lower conductivities compared to single alkali doped glassesand this has been attributed to a mixed alkali effect.
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| 10. |
- Bih, H., et al.
(författare)
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Pentaammonium heptasodium [bis(μ5-phosphato) pentakis (μ2-oxido)-decaoxidopentamolybdenum(VI)] henicosahydrate
- 2010
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Ingår i: Acta Crystallographica Section E. - 1600-5368. ; E66, s. 20-21
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Tidskriftsartikel (refereegranskat)abstract
- The title compound, (NH4)(5)Na-7[Mo5P2O23](2)center dot 21H(2)O, was prepared under atmospheric conditions in aqueous solution at room temperature. The structure contains the [Mo5P2O23](6-) heteropolyoxometallate anion, which has been previously reported a number of times with a variety of differing countercations. Each anion is built up of five MoO6 octahedra sharing an edge and forming a ring which is closed by common corners of the terminal octahedra. The rings are closed on both sides by two asymmetric PO4 tetrahedra, sharing three corners with three MoO6 octahedra. The anions are chiral and the two independent anions in the asymmetric unit were arbitarily chosen with the same chirality, but the centrosymmetric crystal contains both enantiomers. The structure can alternatively be described as a succession of layers parallel to (101), formed by the [Mo5P2O23](6-) anions and linked by sodium chains. Water molecules and ammonium ions fill the remaining space and ensure the cohesion through extensive N-H center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonding.
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