Youssef TAMRAOUI | Université Hassan 2 (original) (raw)
Papers by Youssef TAMRAOUI
BaCO3, SrCO3, NiO, MoO3 precursors were used as starting materials in the synthesis of double per... more 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.
A double perovskite BaSrMgTeO 6 has been synthesized and characterized by physical techniques: X-... more A double perovskite BaSrMgTeO 6 has been synthesized and characterized by physical techniques: X-ray diffraction, and diffuse reflectance spectroscopy. It crystallizes at room temperature, in the cubic system with unit cell parameters: a=8.018Å (S.G Fm-3m) and shows an almost perfect ordering between Mg 2+ and Te 6+ cations at the B substructure. Based on Density Functional Theory (DFT), and using full Potential-linearized Augmented Plane Wave (FP-LAPW) method with the Generalized Gradient Approximation (GGA), implemented in the Wien2k package, we have investigated electronic and optical properties of such material. The optical band gap obtained with GGA approximation is equal to 2.8 eV, which is in good agreement with our experimental results. We found that transmittance T is stable and reaches the average of 90% in both experimental and theoretical studies.
The symposium ISPDS2 has taken place in Meknes (Morocco) in October, 2017. It has gathered specia... more The symposium ISPDS2 has taken place in Meknes (Morocco) in October, 2017. It has gathered specialists of various fields who presented their work in connection with the problematics of data storage. This conference volume contains 75 abstracts of communications presented at the meeting as invited conferences, talks, or posters. Various topics are covered.
Materials Chemistry and Physics, 2022
Physica B: Condensed Matter, 2021
In this work, we report on the synthesis of Barium Strontium Tungstate (Ba1-xSrx)WO4 powders with... more In this work, we report on the synthesis of Barium Strontium Tungstate (Ba1-xSrx)WO4 powders with (x = 0 ; 0.25 ; 0.5 ; 0.75 and 1.0). The obtained powders were analyzed by X-ray diffraction (XRD), Raman spectroscopy and also optimised by Density functional theory (DFT) calculations. XRD patterns showed that (Ba1-xSrx)WO4 powders present a scheelite-type tetragonal structure. Rietveld refinements showed that the samples crystallized with tetragonal symmetry, S.G. I41/a. and lattice parameters : a~ 5.07 Å and c~ 11.6 Å. The scheelite structure can be represented by WO4 tetrahedra isolated from each other and connected by the summits with Baand Srpolyhedrons. Raman spectra proved the evidence of a tetragonal structure due to W-O antisymmetric stretching vibration into the [WO4] tetrahedron groups. Density functional theory (DFT) using the Plane-Wave Self-Consistent Field (PWscf) with generalized gradient approximation (GGA) were carried out for the scheelite materials (Ba1-xSrx)WO4 in...
Journal of Building Engineering, 2021
Abstract The main objective of this research is the development and characterization of an acidic... more Abstract The main objective of this research is the development and characterization of an acidic geopolymer based on local raw materials, namely Moroccan kaolinitic clay with phosphoric acid coming from the Moroccan phosphate industry. The influence of the calcination temperature and the liquid/solid ratio (L/S) on the mechanical and microstructural properties was evaluated. The thermal behavior of the optimized formulation was studied using FTIR, XRD, SEM, TGA/DTA, and compressive strength tests. The findings shows that highest value of the compressive strength presented by the elaborated geopolymer was about 67 MPa, which prepared by kaolin calcined at 900°C with a ratio of L/S=1. In addition the increase in L/S ration led to a significant decrease in the mechanical strength. The thermal behavior assessment of the optimized geopolymer reveals that these materials exhibit excellent mechanical properties even when exposed to a very high temperature of 1100°C with a compressive strength of 13MPa. Microstructural analysis of the thermally treated geopolymer indicates its crystallization start at a temperatures above 500°C with the appearance of new crystalline phases stable at elevated temperatures, notably phosphocristobalite and cristobalite. The outcomes indicate that the use of Moroccan clay in the synthesis of acid geopolymers leads to excellent results with adequate calcination temperature and L/S ratio.
Journal of Electroceramics, 2021
A series of double-perovskite oxides Sr 2 Sr 1-x Ca x TeO 6 (0 ≤ x ≤ 1) samples have been prepare... more A series of double-perovskite oxides Sr 2 Sr 1-x Ca x TeO 6 (0 ≤ x ≤ 1) samples have been prepared in order to study the effect of composition on phase formation and the related optical properties. The objective of this work is to study the possibility of calcium insertion with different percentages since calcium in known to enhance the electrical properties. In this work a well detailed structure and phase transitions investigation of the compounds were conducted and probed by X-ray diffraction and Raman spectroscopy techniques at room temperature. Both Rietveld refinements and Raman studies revealed that two phase transitions took place as the calcium amount x increases; a first from a triclinic to a hexagonal in the range 0.1 < x < 0.25 and a second from the hexagonal to a monoclinic structure in the range 0.5 < x < 0.6. The optical absorption α(λ) was also determined as a function of calcium content in the series samples using UV-vis analysis. It was revealed that a remarkable change occured in the cutoff wavelength, confirming the sequence of phase transitions C1 → R3 m → P2 1 /n. The optical band gap measurements showed that the triclinic Sr 3 TeO 6 and the monoclinic Sr 2 CaTeO 6 phases have band gap values of 2.75 and 2.81 eV, respectively. When the calcium increased to x = 0.25 (Sr 2.75 Ca 0.25 TeO 6) , remarkable decrease of the band gap value was observed, with Eg = 2.627 eV.
Materials Today: Proceedings, 2020
Powder Diffraction, 2018
Ceramics of Sr2CaFe2WO9 and Sr2PbFe2TeO9 double perovskites have been prepared in polycrystalline... more 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) Å, c = 7.8389(1) Å for Sr2CaFe2WO9, and a = 5.5994(15) Å, c = 7.8979(30) Å 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.
Journal of Inorganic and Organometallic Polymers and Materials, 2020
Polycrystalline samples of the series of triple perovskites Sr3−xPbxFe2TeO9 (0 ≤ x ≤ 2.25) (SPFTO... more 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), Mössbauer 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¯m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R{\overline{3}}m$$\end{document} (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 Mössbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. 57Fe Mössbauer 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.
The Journal of Physical Chemistry C, 2018
A cobalt iron oxyphosphate CoFeOPO 4 @C (abbreviated as CFP@C) anode was prepared via a solid-sta... more A cobalt iron oxyphosphate CoFeOPO 4 @C (abbreviated as CFP@C) anode was prepared via a solid-state route, and its electrochemical performance was investigated vs. Li + /Li over a wide voltage range of 0.01-3.0 V at different current rates C/n (n= 20, 10, 5, 2 and 1). This anode material is able to intercalate more than six lithium ions into the structure at the C/10 current rate, delivering a specific capacity of 748.23 mAh g-1 , which is much higher than the theoretical capacity (593.7 mAh g-1) calculated when the insertion of a single lithium ion is considered. A reversible capacity of 200 mAhg-1 was maintained after 30 cycles. Raman spectroscopy confirmed the incorporation of carbon layers into the CoFeOPO 4 @C composite. Scanning electronic microscopy revealed that CFP@C particles have an angular-flake shape with particle sizes ranging between 1 and 5 µm. In situ X-ray absorption spectroscopy of Fe and Co at the K-edge showed that both transition metals are active during the whole discharge and charge. In operando high energy X-ray diffraction revealed that this material undergoes a gradual evolution of the structure with lower crystallinity after the first discharge. Correlating electrochemical performance to the structural and electronic features indicated that the cycling mechanism of the CFP@C anode material exhibits a combination of intercalation and conversion processes.
Electrochimica Acta, 2018
Understanding the electrochemical lithiation/delithiation process in the anode material for lithi... more Understanding the electrochemical lithiation/delithiation process in the anode material for lithium ion batteries NiFeOPO 4 /C using ex-situ X-ray absorption near edge spectroscopy and in-situ synchrotron X-ray, Electrochimica Acta (2018),
Materials Research Express, 2017
Sr 2 ZnTeO 6 double-perovskite oxide has been synthesized using solid state chemistry. As synthes... more Sr 2 ZnTeO 6 double-perovskite oxide has been synthesized using solid state chemistry. As synthesized, the crystalline structure of Sr 2 ZnTeO 6 , 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 °C-567 °C. It is found that two of three observed bending Raman vibrations merge together at a temperature of around 120 °C, indicating a Sr 2 ZnTeO 6 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 °C, which is interpreted as a phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.
Journal of Molecular Structure, 2017
Structures of Sr 2Àx Ca 1þx TeO 6 double perovskites have been studied by the profile analysis of... more Structures of Sr 2Àx Ca 1þx TeO 6 double perovskites have been studied by the profile analysis of X-ray diffraction data and Raman spectroscopy at room temperature. This series adopts a monoclinic symmetry for the compositions (0 x 0.5) with P2 1 /n as space group and a triclinic system with P1 space group for the compositions (0.5 < x 2). These results were confirmed by the observed tolerance factor calculated from the distances obtained from the Rietveld refinements which indicates that the true tilt system for the compositions range (0.5 < x 2) is the triclinic tilt system. Clear changes in the Raman modes centered at 600, 610 and 620 cm À1 and the FWHM of OeTeeO bending vibrations, centered at 738 cm À1 confirmed that the triclinic symmetry takes place between the compositions x ¼ 0.5 and x ¼ 1. Furthermore, Raman spectroscopy studies at high temperature were done for Ca 3 TeO 6. For this compound, considerable changes in the temperature dependence of the modes were well illustrated.
Journal of Alloys and Compounds, 2016
[Sr2CaWO6]x double perovskite tungsten oxides](https://attachments.academia-assets.com/88958756/thumbnails/1.jpg)
](Journal of Solid State Chemistry, 2015
Sequence of phase transitions induced by chemical composition and High temperature in [Ba 2 CaWO ... more Sequence of phase transitions induced by chemical composition and High temperature in [Ba 2 CaWO 6 ](1-x)[Sr 2 CaWO 6 ]x double perovskite tungsten o x i d e s ,
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 26, 2015
Synthesis of apatites, Na1-xKxCaPb3(PO4)3 0⩽x⩽1, with anion vacancy were carried out using solid ... more 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 P63/m (No. 176). Rietveld refinements showed that around 90% of Pb(2+) cations are located in the (6h) sites, the left amount of Pb(2+) cations are located in the (4f) sites; 27-31% of Ca(2+) cations are located in the (6h) sites, the left amount of Ca(2+) 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 Pb(2+)/Ca(2+) 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 Pb(2+)/Ca(2+) and half by Na(+)/K(+) mixed cations. The assignment of the observed frequencies in the Raman and infrare...
Applied Physics Letters, 2013
ABSTRACT Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was pr... more 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.
BaCO3, SrCO3, NiO, MoO3 precursors were used as starting materials in the synthesis of double per... more 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.
A double perovskite BaSrMgTeO 6 has been synthesized and characterized by physical techniques: X-... more A double perovskite BaSrMgTeO 6 has been synthesized and characterized by physical techniques: X-ray diffraction, and diffuse reflectance spectroscopy. It crystallizes at room temperature, in the cubic system with unit cell parameters: a=8.018Å (S.G Fm-3m) and shows an almost perfect ordering between Mg 2+ and Te 6+ cations at the B substructure. Based on Density Functional Theory (DFT), and using full Potential-linearized Augmented Plane Wave (FP-LAPW) method with the Generalized Gradient Approximation (GGA), implemented in the Wien2k package, we have investigated electronic and optical properties of such material. The optical band gap obtained with GGA approximation is equal to 2.8 eV, which is in good agreement with our experimental results. We found that transmittance T is stable and reaches the average of 90% in both experimental and theoretical studies.
The symposium ISPDS2 has taken place in Meknes (Morocco) in October, 2017. It has gathered specia... more The symposium ISPDS2 has taken place in Meknes (Morocco) in October, 2017. It has gathered specialists of various fields who presented their work in connection with the problematics of data storage. This conference volume contains 75 abstracts of communications presented at the meeting as invited conferences, talks, or posters. Various topics are covered.
Materials Chemistry and Physics, 2022
Physica B: Condensed Matter, 2021
In this work, we report on the synthesis of Barium Strontium Tungstate (Ba1-xSrx)WO4 powders with... more In this work, we report on the synthesis of Barium Strontium Tungstate (Ba1-xSrx)WO4 powders with (x = 0 ; 0.25 ; 0.5 ; 0.75 and 1.0). The obtained powders were analyzed by X-ray diffraction (XRD), Raman spectroscopy and also optimised by Density functional theory (DFT) calculations. XRD patterns showed that (Ba1-xSrx)WO4 powders present a scheelite-type tetragonal structure. Rietveld refinements showed that the samples crystallized with tetragonal symmetry, S.G. I41/a. and lattice parameters : a~ 5.07 Å and c~ 11.6 Å. The scheelite structure can be represented by WO4 tetrahedra isolated from each other and connected by the summits with Baand Srpolyhedrons. Raman spectra proved the evidence of a tetragonal structure due to W-O antisymmetric stretching vibration into the [WO4] tetrahedron groups. Density functional theory (DFT) using the Plane-Wave Self-Consistent Field (PWscf) with generalized gradient approximation (GGA) were carried out for the scheelite materials (Ba1-xSrx)WO4 in...
Journal of Building Engineering, 2021
Abstract The main objective of this research is the development and characterization of an acidic... more Abstract The main objective of this research is the development and characterization of an acidic geopolymer based on local raw materials, namely Moroccan kaolinitic clay with phosphoric acid coming from the Moroccan phosphate industry. The influence of the calcination temperature and the liquid/solid ratio (L/S) on the mechanical and microstructural properties was evaluated. The thermal behavior of the optimized formulation was studied using FTIR, XRD, SEM, TGA/DTA, and compressive strength tests. The findings shows that highest value of the compressive strength presented by the elaborated geopolymer was about 67 MPa, which prepared by kaolin calcined at 900°C with a ratio of L/S=1. In addition the increase in L/S ration led to a significant decrease in the mechanical strength. The thermal behavior assessment of the optimized geopolymer reveals that these materials exhibit excellent mechanical properties even when exposed to a very high temperature of 1100°C with a compressive strength of 13MPa. Microstructural analysis of the thermally treated geopolymer indicates its crystallization start at a temperatures above 500°C with the appearance of new crystalline phases stable at elevated temperatures, notably phosphocristobalite and cristobalite. The outcomes indicate that the use of Moroccan clay in the synthesis of acid geopolymers leads to excellent results with adequate calcination temperature and L/S ratio.
Journal of Electroceramics, 2021
A series of double-perovskite oxides Sr 2 Sr 1-x Ca x TeO 6 (0 ≤ x ≤ 1) samples have been prepare... more A series of double-perovskite oxides Sr 2 Sr 1-x Ca x TeO 6 (0 ≤ x ≤ 1) samples have been prepared in order to study the effect of composition on phase formation and the related optical properties. The objective of this work is to study the possibility of calcium insertion with different percentages since calcium in known to enhance the electrical properties. In this work a well detailed structure and phase transitions investigation of the compounds were conducted and probed by X-ray diffraction and Raman spectroscopy techniques at room temperature. Both Rietveld refinements and Raman studies revealed that two phase transitions took place as the calcium amount x increases; a first from a triclinic to a hexagonal in the range 0.1 < x < 0.25 and a second from the hexagonal to a monoclinic structure in the range 0.5 < x < 0.6. The optical absorption α(λ) was also determined as a function of calcium content in the series samples using UV-vis analysis. It was revealed that a remarkable change occured in the cutoff wavelength, confirming the sequence of phase transitions C1 → R3 m → P2 1 /n. The optical band gap measurements showed that the triclinic Sr 3 TeO 6 and the monoclinic Sr 2 CaTeO 6 phases have band gap values of 2.75 and 2.81 eV, respectively. When the calcium increased to x = 0.25 (Sr 2.75 Ca 0.25 TeO 6) , remarkable decrease of the band gap value was observed, with Eg = 2.627 eV.
Materials Today: Proceedings, 2020
Powder Diffraction, 2018
Ceramics of Sr2CaFe2WO9 and Sr2PbFe2TeO9 double perovskites have been prepared in polycrystalline... more 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) Å, c = 7.8389(1) Å for Sr2CaFe2WO9, and a = 5.5994(15) Å, c = 7.8979(30) Å 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.
Journal of Inorganic and Organometallic Polymers and Materials, 2020
Polycrystalline samples of the series of triple perovskites Sr3−xPbxFe2TeO9 (0 ≤ x ≤ 2.25) (SPFTO... more 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), Mössbauer 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¯m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R{\overline{3}}m$$\end{document} (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 Mössbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. 57Fe Mössbauer 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.
The Journal of Physical Chemistry C, 2018
A cobalt iron oxyphosphate CoFeOPO 4 @C (abbreviated as CFP@C) anode was prepared via a solid-sta... more A cobalt iron oxyphosphate CoFeOPO 4 @C (abbreviated as CFP@C) anode was prepared via a solid-state route, and its electrochemical performance was investigated vs. Li + /Li over a wide voltage range of 0.01-3.0 V at different current rates C/n (n= 20, 10, 5, 2 and 1). This anode material is able to intercalate more than six lithium ions into the structure at the C/10 current rate, delivering a specific capacity of 748.23 mAh g-1 , which is much higher than the theoretical capacity (593.7 mAh g-1) calculated when the insertion of a single lithium ion is considered. A reversible capacity of 200 mAhg-1 was maintained after 30 cycles. Raman spectroscopy confirmed the incorporation of carbon layers into the CoFeOPO 4 @C composite. Scanning electronic microscopy revealed that CFP@C particles have an angular-flake shape with particle sizes ranging between 1 and 5 µm. In situ X-ray absorption spectroscopy of Fe and Co at the K-edge showed that both transition metals are active during the whole discharge and charge. In operando high energy X-ray diffraction revealed that this material undergoes a gradual evolution of the structure with lower crystallinity after the first discharge. Correlating electrochemical performance to the structural and electronic features indicated that the cycling mechanism of the CFP@C anode material exhibits a combination of intercalation and conversion processes.
Electrochimica Acta, 2018
Understanding the electrochemical lithiation/delithiation process in the anode material for lithi... more Understanding the electrochemical lithiation/delithiation process in the anode material for lithium ion batteries NiFeOPO 4 /C using ex-situ X-ray absorption near edge spectroscopy and in-situ synchrotron X-ray, Electrochimica Acta (2018),
Materials Research Express, 2017
Sr 2 ZnTeO 6 double-perovskite oxide has been synthesized using solid state chemistry. As synthes... more Sr 2 ZnTeO 6 double-perovskite oxide has been synthesized using solid state chemistry. As synthesized, the crystalline structure of Sr 2 ZnTeO 6 , 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 °C-567 °C. It is found that two of three observed bending Raman vibrations merge together at a temperature of around 120 °C, indicating a Sr 2 ZnTeO 6 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 °C, which is interpreted as a phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.
Journal of Molecular Structure, 2017
Structures of Sr 2Àx Ca 1þx TeO 6 double perovskites have been studied by the profile analysis of... more Structures of Sr 2Àx Ca 1þx TeO 6 double perovskites have been studied by the profile analysis of X-ray diffraction data and Raman spectroscopy at room temperature. This series adopts a monoclinic symmetry for the compositions (0 x 0.5) with P2 1 /n as space group and a triclinic system with P1 space group for the compositions (0.5 < x 2). These results were confirmed by the observed tolerance factor calculated from the distances obtained from the Rietveld refinements which indicates that the true tilt system for the compositions range (0.5 < x 2) is the triclinic tilt system. Clear changes in the Raman modes centered at 600, 610 and 620 cm À1 and the FWHM of OeTeeO bending vibrations, centered at 738 cm À1 confirmed that the triclinic symmetry takes place between the compositions x ¼ 0.5 and x ¼ 1. Furthermore, Raman spectroscopy studies at high temperature were done for Ca 3 TeO 6. For this compound, considerable changes in the temperature dependence of the modes were well illustrated.
Journal of Alloys and Compounds, 2016
Journal of Solid State Chemistry, 2015
Sequence of phase transitions induced by chemical composition and High temperature in [Ba 2 CaWO ... more Sequence of phase transitions induced by chemical composition and High temperature in [Ba 2 CaWO 6 ](1-x)[Sr 2 CaWO 6 ]x double perovskite tungsten o x i d e s ,
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 26, 2015
Synthesis of apatites, Na1-xKxCaPb3(PO4)3 0⩽x⩽1, with anion vacancy were carried out using solid ... more 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 P63/m (No. 176). Rietveld refinements showed that around 90% of Pb(2+) cations are located in the (6h) sites, the left amount of Pb(2+) cations are located in the (4f) sites; 27-31% of Ca(2+) cations are located in the (6h) sites, the left amount of Ca(2+) 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 Pb(2+)/Ca(2+) 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 Pb(2+)/Ca(2+) and half by Na(+)/K(+) mixed cations. The assignment of the observed frequencies in the Raman and infrare...
Applied Physics Letters, 2013
ABSTRACT Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was pr... more 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.