| 1. |
- El Aamrani, Abdelaziz, et al.
(författare)
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Synthesis, crystal Structure and temperature induced phase transition in Ba1/5Sr4/5NiMoO6 double perovskite oxide: : Study by X-ray diffraction and Raman spectroscopy
- 2017
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Ingår i: Journal of Applied Surfaces and Interfaces. ; 2:1-3, s. 27-33
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Tidskriftsartikel (refereegranskat)abstract
- BaCO3, SrCO3, NiO, MoO3 precursors were used as starting materials in the synthesis of double perovskite Ba1/5Sr4/5NiMoO6, and their crystal structure at room tempertaure was solved using X-ray powder diffraction. The Rietveld analysis of X–ray powder diffraction patterns show that both compounds adopt a tetragonal structure with space group I4/m, with unit cell parameters a= 5.58537(1) Å, c=7.9066(2) Å. The structure can be represented as a three-dimensional network of alternating NiO6 and MoO6 octahedra, with Ba and Sr atoms occupying the interstitial spaces. Temperature-induced phase transitions of Ba1/5Sr4/5NiMoO6 were investigated by mean of Raman spectroscopy technique at high temperature up to 392 °C. remarkable in the behaviuor of temperature dependence of the modes has been interpreted as a phase transition from the tetragonal (I4/m) to the cubic () structure.
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| 2. |
- El Hachmi, Abdelhadi, et al.
(författare)
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Synthesis and Rietveld refinements of new ceramics Sr2CaFe2WO9 and Sr2PbFe2TeO9 perovskites
- 2018
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Ingår i: Powder Diffraction. - : J C P D S-INT CENTRE DIFFRACTION DATA. - 0885-7156 .- 1945-7413. ; 33:2, s. 134-140
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Tidskriftsartikel (refereegranskat)abstract
- Ceramics of Sr2CaFe2WO9 and Sr2PbFe2TeO9 double perovskites have been prepared in polycrystalline form by solid-state technique, in the air. The crystalline structure was analyzed using X-ray powder diffraction (XRPD) at room temperature. Rietveld analysis of XRPD) patterns show that both compounds adopt a tetragonal structure with space group I4/m, with unit cell parameters a = 5.5453(1) angstrom, c = 7.8389(1) angstrom for Sr(2)CaFc(2)WO(9), and a = 5.5994(15) angstrom, c = 7.8979(30) angstrom for Sr2PbFe2TeO9. A certain degree of anti-site disordering of W and/or Te and Fe on the B -sites have been detected, indicating the presence of a partial amount of W and/or Te at Fe positions and vice versa.
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| 3. |
- El Hachmi, Abdelhadi, et al.
(författare)
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Temperature induced structural phase transition in Sr3-xCaxFe2TeO9 (0 <= x <= 1) probed by Raman and Mossbauer techniques
- 2017
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1141, s. 484-494
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Tidskriftsartikel (refereegranskat)abstract
- A series of perovskites Sr3-xCaxFe2TeO9 (0 <= x <= 1) have been prepared in polycrystalline form by solid-state reaction method in air. These materials have been studied by X-ray powder diffraction method (XRPD) and Raman spectroscopy. An analysis of the XRD patterns at room temperature has shown that these compounds crystallize in a tetragonal system, space group I4/m. The structure contains alternating (Fe/Te)(2a)O-6 and (Fe/Te)(2b)O-6 octahedra, tilted in anti-phase in the basal ab-plane. The study of Raman spectroscopy at various temperatures shows a transition from tetragonal to cubic phase: I4/m -> Fm (3) over bar m. This phase transition occurs at high-temperature. Analysis of Raman spectra recorded at several temperatures shows that this phase transition appears near similar to 375 degrees C for (x = 0), similar to 435 degrees C for (x = 0.5) and similar to 451 degrees C for (x = 1). A proportional and gradual increase of temperature phase transition is observed as function of the calcium amount.
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| 4. |
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| 5. |
- Ezzahi, A., et al.
(författare)
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X-ray diffraction and Raman spectroscopy studies of BaSrMWO6 (M=Ni, Co, Mg) double perovskite oxides
- 2011
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 985:2-3, s. 339-345
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report on the crystal structure and Raman spectroscopy of BaSrMWO6 (M=Ni, Co, Mg) double perovskite oxides. The results showed that the Ni, Co and Mg containing compounds crystallize in a cubic system with the space group Fm-3 in. The double perovskite structure can be represented as a three-dimensional network of alternating MO6 and WO6 octahedra, with Ba- and Sr-atoms occupying the interstitial spaces. The Raman spectra of this crystalline perovskite oxides are interpreted by means of factor group analysis in terms of space group Fm-3 m. Assignments of the W-O vibrational stretching and bending modes have been made. High temperature Raman spectroscopy of BaSrNiWO6 showed that all lattice modes illustrate a linear decrease in wavenumbers while temperature is increased. No discontinuities, in the temperature changes, in wavenumber observed for all modes recorded: indicating that the structure remains cubic and stable up the highest temperature studied here.
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| 6. |
- Li, Nana, et al.
(författare)
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Pressure-Induced Structural and Electronic Transition in Sr2ZnWO6 Double Perovskite
- 2016
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 55:13, s. 6770-6775
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Tidskriftsartikel (refereegranskat)abstract
- High-pressure structural and electrical properties of Sr2ZnWO6 double perovskite were investigated using in situ angle-dispersive synchrotron X-ray diffraction (XRD), Raman, and alternating current (AC) impedance spectroscopy. A structural transition from monoclinic (P2(1)/n) to triclinic (P (1) over bar) phase around 9 GPa was observed due to the pressure-induced distortion of (W, Zn)O-6 octahedron. In situ high-pressure Raman spectroscopy showed the increasing interaction among O-W-O in WO6 octahedron with pressure and a transition pressure consistent with the XRD results. From the AC impedance spectroscopy measurements, the resistivity increased steeply by similar to 1 order of magnitude around 11 GPa, indicating an electronic transition accompanying the symmetry change. The increase in the interaction among O-W-O enhances the attraction of O2- electrons toward W6+, thus increasing the covalence, which in turn lowers the charge transfer energy between O2- and W6+ and induces the resistivity increase under high pressure.
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| 7. |
- Li, Nana, et al.
(författare)
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Structural and electronic phase transitions of Co2Te3O8 spiroffite under high pressure
- 2019
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:24
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Tidskriftsartikel (refereegranskat)abstract
- The structural and electronic phase transitions of Co2Te3O8 spiroffite have been studied with a suite of in situ high-pressure characterization techniques including synchrotron x-ray diffraction, Raman, x-ray emission spectroscopy, UV-vis absorption, and electrical transport measurement. Two pressure-induced phase transitions were observed at about 6.9 and 14.4 GPa. The first transition is attributed to a small spin transition of Co along with discontinuity in unit-cell volume change, while the second one represents a first-order phase transition with a volume collapse of 4.5%. The latter transition is accompanied by the relaxation of distortion in CoO6 octahedron, which enhances the crystal-field strength inhibiting the occurrence of spin transition. What is more, the competition between contributions of electrons and oxygen ion to the overall conductivity is observed and affected by the phase transition under high pressure. This demonstration provides insights into the relationship between the lattice-structural and spin degrees of freedom, and highlights the impact of pressure on the control of structural and electronic states of a given material for optimized functionalities.
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| 8. |
- Manoun, Bouchaib, et al.
(författare)
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Crystal structure and high temperature Raman spectroscopy of Sr2ZnTeO6 double perovskite
- 2017
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Ingår i: Materials Research Express. - : IOP PUBLISHING LTD. - 2053-1591. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- Sr2ZnTeO6 double-perovskite oxide has been synthesized using solid state chemistry. As synthesized, the crystalline structure of Sr2ZnTeO6, refined using x-ray diffraction, is monoclinic having the space group I2/m. Structural phase transitions are studied using Raman spectroscopy in the temperature range 25 degrees C-567 degrees C. It is found that two of three observed bending Raman vibrations merge together at a temperature of around 120 degrees C, indicating a Sr2ZnTeO6 phase transition from the monoclinic (I2/m) to the tetragonal (I4/m). Furthermore, a temperature-dependence change-rate of external and O-Te-O bending modes and stretching modes are detected at 270 degrees C, which is interpreted as a phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.
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| 9. |
- Manoun, Bouchaib, et al.
(författare)
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High Temperature Raman Spectroscopy studies of the phase transitions in Sr2NiWO6 and Sr2MgWO6 double perovskite oxides
- 2010
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 971:1-3, s. 18-22
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report on high temperature Raman spectroscopy studies (up to 550 °C) of the phase transitions in Sr2BWO6 (B = Ni, Mg) double perovskite oxides. For both compounds, the transition from the tetragonal (I4/m) phase to the cubic (Fm-3m) phase is accompanied by considerable changes in the temperature dependence of the modes. To better view this phase transition, the FWHM temperature dependence of the most intense modes were studied; by this study, we have obtained a sensitive guide to the onset of the phase transition. A large increase of the FWHM with increasing temperature is observed for all modes in the spectrum, clear transitional effects were observed: the width behaves in a linear way as a function of temperature; when the temperature reached around 300 °C, a drop in the width of this mode was observed; thus, showing the phase transition occurrence for both compounds. This drop is much more illustrated in Ni-containing compound than in Sr2MgWO6.
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| 10. |
- Manoun, Bouchaib, et al.
(författare)
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Temperature and nickel substitution effects on the phase transitions in the Sr2Zn1-xNixWO6 ( 0 <= x <= 1) double perovskite
- 2016
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 689, s. 233-245
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Tidskriftsartikel (refereegranskat)abstract
- Sr2Zn1-xNixWO6 solid solutions (with 0 <= x <= 1) have been synthesized by solid-state reactions, and characterized by X-Ray diffraction and Raman spectroscopy. The X-Ray powder diffraction (XRD) data at room temperature shows a systematical change of structure vs. nickel content: the compound adopts a monoclinic phase with a P2(1)/n space group with 0 <= x <= 0.18, a tetragonal structure with a I4/m space group with x = 0.25, and a tetragonal structure with a I4/mmm space group with 0.5 <= x <= 1. Further in-situ Raman study at elevated temperature (up to 555 degrees C) shows the pristine monoclinic phase (0 <= x <= 0.18) follows the phase path: monoclinic (P2(1)/n) -> tetragonal (I4/m) -> tetragonal (I4/ mmm) -> cubic (Fm (3) over barm); for the compound Sr2Zn0.75Ni0.25WO6, it involves later two phase transitions as tetragonal (I4/m) -> tetragonal (I4/mmm) -> cubic (Fm (3) over barm); and for the 0.5 <= x <= 1 compounds, only one phase transition I4/mmm to Fm (3) over barm was observed. The combined investigation of composition and temperature provides us a complete understanding of chemical substitution and temperature effect on structural phase transition.
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