Showing papers by "Dany Carlier published in 2010"
TL;DR: In this paper, the NaMnFe2(PO4)3 alluaudite phase was prepared either by classical solid-state chemistry or by the sol−gel method and its structure was investigated by Rietveld refinement of XRD and neutron diffraction data in order to precisely determine the cationic distribution.
Abstract: The NaMnFe2(PO4)3 alluaudite phase was prepared either by classical solid-state chemistry or by the sol−gel method. Its structure was investigated by Rietveld refinement of XRD and neutron diffraction data in order to precisely determine the cationic distribution. This 3D skeleton structure exhibits two types of 1D tunnels where the Na+ ions are localized. The material obtained by the sol−gel method exhibits a composition very close to the ideal one, contrary to previous works reported in literature. This study leads us to propose the following formulation for our sample: (Na0.81)A(1)(Na0.19)A(2)′(MnII0.87FeII0.13)M(1)(FeIII1.87MnIII0.13)M(2)(PO4)3. The iron/manganese exchange was revealed from neutron data and was supported by Mossbauer spectroscopy (presence of small amount of Fe2+ ions in the M(1) type site). The stability of the various Na+ ions sites within the tunnels were studied by DFT calculations. The intercalation/deintercalation properties of NaMnFe2(PO4)3 as positive electrode were tested in ...
132 citations
TL;DR: In this article, a nominal composition Na2/3MnO2 was prepared by solid state reaction between Na2CO3 and MnCO3 at 1000°C, and the composition and structure of NaxMnNO2 were controlled by the rate of cooling from the temperature of preparation; the overstoichiometric Mn4+ ions were accommodated in the hexagonal modification by creating of vacancies in the MnO2 layers.
117 citations
TL;DR: For the first time, lithium intercalation was shown to occur in LiFePO4(OH) through the reduction of Fe3+ to Fe2+ at an average voltage of ~2.3 V (vs.
Abstract: Pure tavorite LiFePO4(OH) was synthesized through a hydrothermal route. A fine structural analysis was done by X-ray and neutron diffraction techniques. The structure consists of a three-dimensional network with iron(III) octahedra (FeO6) sharing corners, forming chains that run along the b direction. These chains are interconnected by PO4 tetrahedra, such as the resulting framework encloses tunnels of two different sizes running along the a and c axis. The lithium and hydrogen atoms were precisely localized in these tunnels. Theoretical (GGA + U) calculations performed for LiFePO4X materials (X = OH, F) confirmed our results and revealed that a unique lithium position is expected in LiFePO4(OH), as experimentally observed. For the first time, lithium intercalation was shown to occur in LiFePO4(OH) through the reduction of Fe3+ to Fe2+ at an average voltage of ∼2.3 V (vs. Li+/Li) with a good cyclability.
62 citations
TL;DR: A new iron(III) phosphate FePO4·H2O phase was obtained from tavorite LiFePO4(OH) through a Li+/H+ exchange.
Abstract: A new iron(III) phosphate FePO4·H2O, isostructural to already reported VPO4·H2O and MnPO4·H2O phases, was obtained from tavorite LiFePO4(OH) through a Li+/H+ exchange. The composition of this new phase was confirmed by different chemical analyses. The ion-exchange reaction was shown to be topotactic; indeed the structures of LiFePO4OH and FePO4·H2O are very similar and both are characterized by chains of FeO6 octahedra, interconnected through PO4 tetrahedra, such as the resulting frameworks enclose different types of tunnels. A neutron diffraction study has allowed the localization of hydrogens in the FePO4·H2O structure, revealing that the two hydrogen atoms are linked to the oxygen atoms shared by two adjacent FeO6 octahedra. The presence of these “H2O-like” groups inserted along the FeO6 chains leads to a considerable distortion of the FeO6 octahedra. The nature of the −OH and −OH2 groups in LiFePO4OH and FePO4·H2O, respectively, was confirmed by vibrational spectroscopies. Lithium intercalation was sh...
57 citations
TL;DR: In this paper, a powder of Na3Fe3(PO4)4 was obtained by solid state reaction and crystallized in monoclinic space group C2/c.
Abstract: For the first time, a powder of Na3Fe3(PO4)4 was obtained by solid state reaction. It crystallizes in monoclinic space group C2/c in good agreement with previous studies of a single crystal. The Rietveld refinement of the XRD pattern showed line broadening of some diffraction lines associated with size and strain effects. Its layered structure can be described by complex layers of corner-sharing FeO6 octahedra connected by PO4 tetrahedra through corner and edge sharing. The Na+ ions are located in the interslab space. The local environments of Fe, Na, and P were characterized by 57Fe Mossbauer spectroscopy and 23Na and 31P MAS NMR. A Second ORder Graphic Extrapolation (SORGE) diagram as introduced by Massiot et al. allowed us to fully interpret the 23Na MAS NMR spectrum that exhibits three signals for two crystallographic Na sites. The electrochemical properties of Na3Fe3(PO4)4 were tested in sodium cells. Ex situ and in situ X-ray diffraction data and Mossbauer spectroscopy measurements indicate that the...
55 citations
TL;DR: The Rietveld refinement of the X-ray and neutron diffraction data coupled with ab initio calculations allowed us for the first time to accurately localize the lithium ions in the alluaudite structure.
Abstract: The alluaudite lithiated phases Li(0.5)Na(0.5)MnFe(2)(PO(4))(3) and Li(0.75)Na(0.25)MnFe(2)(PO(4))(3) were prepared via a sol-gel synthesis, leading to powders with spongy characteristics. The Rietveld refinement of the X-ray and neutron diffraction data coupled with ab initio calculations allowed us for the first time to accurately localize the lithium ions in the alluaudite structure. Actually, the lithium ions are localized in the A(1) and A(1)' sites of the tunnel. Mossbauer measurements showed the presence of some Fe(2+) that decreased with increasing Li content. Neutron diffraction revealed the presence of a partial Mn/Fe exchange between the two transition metal sites that shows clearly that the oxidation state of the element is fixed by the type of occupied site. The electrochemical properties of the two phases were studied as positive electrodes in lithium batteries in the 4.5-1.5 V potential window, but they exhibit smaller electrochemical reversible capacity compared with the non-lithiated NaMnFe(2)(PO(4))(3). The possibility of Na(+)/Li(+) ion deintercalation from (Na,Li)MnFe(2)(PO(4))(3) was also investigated by DFT+U calculations.
42 citations
TL;DR: Li3Fe2(PO4)3 has been characterized by Li NMR in this paper, where the electron spin density transfer mechanism was analyzed by considering different Li environments and using DFT calculations.
Abstract: The monoclinic Li3Fe2(PO4)3 and Li3V2(PO4)3 phosphates are materials for positive electrodes in Li-ion batteries. They also have interesting structures to test and improve the understanding of Li NMR signals in paramagnetic compounds. The position of such signals is governed by the transfer of electron spin density from the transition metal ion to the Li nucleus. These mechanisms are based on delocalization and polarization effects which induce positive and negative Fermi contact shifts, respectively. We have characterized Li3Fe2(PO4)3 by Li NMR. To understand the signals observed, we have analyzed the electron spin density transfer mechanisms (i) by considering the different Li environments, (ii) by using DFT calculations. We compare our analysis to the one very recently reported by Davis et al. These analyses have been extended to Li3V2(PO4)3 studied by NMR by Cahill et al.
22 citations
TL;DR: In this paper, the layered Na 3 Fe 3 (PO 4 ) 4 phase prepared by solid-state reaction was studied as positive electrode in lithium batteries and showed that the intercalation/deintercalation process occurs through a solid solution process and is reversible.
Abstract: The layered Na 3 Fe 3 (PO 4 ) 4 phase prepared by solid-state reaction was studied as positive electrode in lithium batteries. Up to 1.9 Li + ions/f.u. could be intercalated, and only 1.7 Li + ions could be extracted between 4.5 and 2 V vs Li + /Li with an average voltage of around ∼2.8 V. In situ and ex situ X-ray diffraction data and Mossbauer spectroscopy measurements indicate that the intercalation/deintercalation process occurs through a solid solution process and is reversible. To improve its electrochemical performances, Na 3 Fe 3 (PO 4 ) 4 was also prepared via a hydrothermal method that leads to a significant particle size reduction. However, no clear improvements of the cycling performances were observed using this material as positive electrode in sodium and lithium batteries.
21 citations
TL;DR: In this article, the electron spins on the e orbitals of Co2+ ions (e4 t23 electronic configuration) are transferred toward the two different types of Li with opposite polarization, and they have carried out GGA and GGA+U calculations of the electronic structure using the VASP code.
Abstract: Li6CoO4 presents an antifluorite-type structure, with both the Co and Li ions in tetrahedral oxygen coordination. 7Li MAS NMR shows remarkably different shifts (+885 and −232 ppm) for the two different crystallographic types of Li. In order to assign the signals and to understand the mechanisms whereby the electron spins on the e orbitals of Co2+ ions (e4 t23 electronic configuration) are transferred toward the two different types of Li with opposite polarization, we have carried out GGA and GGA+U calculations of the electronic structure using the VASP code. Spin density maps in selected planes of the structure reveal (as expected) that lobes of the t2 orbitals point toward the faces of the CoO4 tetrahedra and can thus overlap with the neighboring Li(2) through empty square pyramidal sites. As concerns Li(1), a mechanism is evidenced where the (filled) e orbitals of Co2+ are polarized by the electron spins in the t2 ones. These polarized e orbitals overlap with Li(1) through the common edge of the tetrahe...
15 citations
TL;DR: In this article, the structural properties of Na2/3Mn1-xFexO2 were studied by Raman spectroscopy and it was found that the crystal structure and the composition of Na 2/3mnO2 display a strong dependence on the history of the thermal treatment.
Abstract: The structural properties of sodium manganates and iron substituted sodium manganates with compositions Na2/3Mn1-xFexO2 (x=0, 1/3 and 2/3) were studied by Raman spectroscopy. The Raman spectroscopy allows distinguishing between layered phases with orthorhombic (Cmcm space group) and hexagonal (P63/mmc space group) distortion. It has been found that the crystal structure and the composition of Na2/3MnO2 display a strong dependence on the history of the thermal treatment. The orthorhombic distorted modification is stabilized at high temperatures (1000 oC). At lower quenching temperature, there is a phase separation into an orthorhombic and a hexagonal modification, concomitant with an increase in the oxidation state of Mn. When Fe substitutes for Mn, the hexagonal modification is stabilized. In order to understand the origin of the Raman spectra of Na2/3Mn1-xFexO2, we have used Na2/3Co2/3Mn1/3O2 as a standard for hexagonal structure, where Co3+ and Mn4+ are statistically distributed in the transition metal layers.
10 citations
TL;DR: The title compound was prepared by solid state reaction of Na2CO3, MnCO3 and FeC2O4 at 900 °C and by the Pechini sol-gel method starting with stoichiometric mixtures of the same educts in aqueous solutions containing citric acid (800 °C, 30 min) as mentioned in this paper.
Abstract: The title compound is prepared by solid state reaction of Na2CO3, MnCO3, FeC2O4, and NH4H2PO4 at 900 °C, and by the Pechini sol—gel method starting with stoichiometric mixtures of the same educts in aqueous solutions containing citric acid (800 °C, 30 min).
TL;DR: In this article, Li+/H+ exchange from an aqueous HNO3 suspension of LiFePO4(OH) at about 60 °C was used to obtain FePO4·H2O.
Abstract: FePO4·H2O is prepared by Li+/H+ exchange from an aqueous HNO3 suspension of LiFePO4(OH) at about 60 °C.