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| 2. |
- El Hachmi, A., et al.
(författare)
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Structural and Mössbauer Studies of Sr(1.5)Ca(1.5)Fe(2.25)Mo(0.75)O(9-delta)and Sr(1.92)Ca(1.08)Fe(2.04)W(9-delta)Double Perovskites
- 2020
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Ingår i: Journal of Structural Chemistry. - : Pleiades Publishing Ltd. - 0022-4766 .- 1573-8779. ; 61:6, s. 861-872
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Tidskriftsartikel (refereegranskat)abstract
- Sr(1.50)Ca(1.50)Fe(2.25)Mo(0.75)O(9-delta)and Sr(1.92)Ca(1.08)Fe(1.04)W(0.96)O(9-delta)double perovskites are synthesized in the polycrystalline form by a solid-state reaction route in air and studied at room temperature using the of PXRD, Raman and Mossbauer spectroscopy techniques. The Rietveld refinement analysis reveals that both compounds adopt a tetragonal system with the space groupI4/m and lattice parametersa=b= 5.5176(1) A andc= 7.8065(2) A for Sr(1.50)Ca(1.50)Fe(2.25)Mo(0.75)O(9-delta)anda=b= 5.5453(1) A andc= 7.8388(1) A for Sr1.92Ca1.08Fe2.04W0.96O9-delta. Raman spectra are consistent with the group theoretical analysis predicted for tetragonal symmetryI4/m(point group C4h5).Fe-57 Mossbauer spectra recorded at room temperature show a paramagnetic behavior for Sr1.50Ca1.50Fe2.25Mo0.75O9-delta, and magnetic ordering for Sr1.92Ca1.08Fe2.04W0.96O9-delta. The isomer shift (delta) and quadrupole splitting (Delta) values are characteristic of high-spin Fe(3+)in a distorted octahedral coordination.
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| 3. |
- El Hachmi, A., et al.
(författare)
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Structural, Magnetic and Optical Properties Study of Tellurium-Based Perovskites : Sr3-xPbxFe2TeO9 (0 <= x <= 2.25)
- 2020
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Ingår i: JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS. - : Springer Science and Business Media LLC. - 1574-1443 .- 1574-1451. ; 30:6, s. 1990-2006
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline samples of the series of triple perovskites Sr3-xPbxFe2TeO9 (0 <= x <= 2.25) (SPFTO) were synthesized using solid state reaction. These materials have been studied by a combination of X-ray powder diffraction (XRPD), Mossbauer spectrometry, Raman and UV-Vis spectroscopies. The crystal structures were resolved by the Rietveld refinement method, and revealed that this Sr3-xPbxFe2TeO9 (0 <= x <= 2.25) system shows one space group change from tetragonal I4/m (0 <= x <= 1) to another tetragonal form I4/mmm (1.25 <= x <= 1.88) and a second transition to hexagonal R3 over bar m (2.08 <= x <= 2.25). An anti-site disordering of Fe and Te on the B sites has been detected indicating the presence of a partial amount of Te at Fe positions and vice versa. The valence state of iron in the Fe site was determined to be Fe(III) by Mossbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. Fe-57 Mossbauer spectra measurements show paramagnetic and magnetic ordering behaviors. The observed Raman spectra as a function of composition show obvious changes on the positions (wavenumbers), the FWHM and the intensities of the modes confirming the phase transformations observed by the XRPD results. These structural transitions led to a distinct change in the optical band gap energy, varying from 2.14 to 1.85 eV.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Lahrich, S., et al.
(författare)
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Elaboration, Rietveld refinements and vibrational spectroscopic study of Na1-xKxCaPb3(PO4)3 lacunar apatites (0 < x < 1)
- 2015
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 145, s. 493-499
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of apatites, Na1-xKxCaPb3(PO4)(3) 0 <= x <= 1, with anion vacancy were carried out using solid state reactions. The solid solution of apatite-type structure crystallize in the hexagonal system, space group P6(3)/m (No. 176). Rietveld refinements showed that around 90% of Pb2+ cations are located in the (6h) sites, the left amount of Pb2+ cations are located in the (4f) sites; 27-31% of Ca2+ cations are located in the (6h) sites, the left amount of Ca2+ cations are located in the (4f) sites. The ninefold coordination sites (4f) are also occupied by the K+ and Na+ monovalent ions. The structure can be described as built up from [PO4](3-) tetrahedra and Pb2+/Ca2+ of sixfold coordination cavities (6h positions), which delimit void hexagonal tunnels running along [001]. These tunnels are connected by cations of mixed sites (4f) which are half occupied by Pb2+/Ca2+ and half by Na+/K+ mixed cations. The assignment of the observed frequencies in the Raman and infrared spectra is discussed on the basis of a unit cell group analysis and by comparison with other apatites. Vibrational spectra of all the compositions are similar and show some linear shifts of the frequencies as a function of the composition toward lower values due the substitutions of Na+ by K+ with a larger radius.
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| 7. |
- 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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| 8. |
- Manoun, B., et al.
(författare)
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Phase transitions in heated Sr2MgTeO6 double perovskite oxide probed by X-ray diffraction and Raman spectroscopy
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:26, s. 261908-
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Tidskriftsartikel (refereegranskat)abstract
- Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O–Te–O bending modes are detected and interpreted as a second 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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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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| 10. |
- Manoun, Bouchaib, et al.
(författare)
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X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2-xSrxMWO6 (M = Ni, Co and 0 <= x <= 2) double perovskite oxides
- 2013
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1045, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction and Raman spectroscopy studies of Sr doped double perovskites compound Ba2-xSrxMWO6 with (M = Ni, Co and 0 <= x <= 2) were investigated. The samples show a transition from cubic to tetragonal phase as a function of composition while increasing strontium amount; both Rietveld refinements and Raman studies showed that this transition occurs between x = 1.2 and 1.4. Furthermore, increasing temperature for the tetragonal compositions (1.4 <= x <= 2), manifest the tetragonal to cubic phase transition. For this series, the transition from tetragonal (I4/m)/to cubic (Fm-3m) shows considerable changes in the composition and temperature dependence of the modes: all the Raman modes show a linear behavior when temperature is increased, then the slope change dramatically indicating the symmetry change from tetragonal to cubic. To better view this phase transition, the full width at half maximum (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 the transition temperature, a drop in the width of this mode was observed.
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