Showing papers by "Dany Carlier published in 2011"
TL;DR: Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.
Abstract: Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.
1,053 citations
TL;DR: P Powder X-ray diffraction analysis revealed that the phase is pure in the absence of long-range ordering of Co and Mn ions in the slab or Na(+) and vacancy in the interslab space, and it appears that the P2 structure is maintained during cycling.
Abstract: Manganese substituted sodium cobaltate, Na(2/3)Co(2/3)Mn(1/3)O(2), with a layered hexagonal structure (P2-type) was obtained by a co-precipitation method followed by a heat treatment at 950 °C. Powder X-ray diffraction analysis revealed that the phase is pure in the absence of long-range ordering of Co and Mn ions in the slab or Na(+) and vacancy in the interslab space. The oxidation states of the transition metal ions were studied by magnetic susceptibility measurements, electron paramagnetic resonance (ESR) and (23)Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The charge compensation is achieved by the stabilization of low-spin Co(3+) and Mn(4+) ions. The capability of Na(2/3)Co(2/3)Mn(1/3)O(2) to intercalate and deintercalate Na(+) reversibly was tested in electrochemical sodium cells. It appears that the P2 structure is maintained during cycling, the cell parameter evolution versus the sodium amount is given. From the features of the cycling curve the formation of an ordered phase for the Na(0.5)Co(2/3)Mn(1/3)O(2) composition is expected.
227 citations
TL;DR: For the first time, a new type of layered oxide exhibiting OPP9-type oxygen packing was evidenced, and its structure presents an ideal alternate ordering of lithium, cobalt, and sodium layers within OP4- type oxygen packing.
Abstract: The composition and synthesis conditions of the (Li/Na)CoO(2) phase with an ordered 1:1 Li/Na stacking alternating with CoO(2) slabs were determined from a careful study of the P2-Na(∼0.7)CoO(2)-O3-LiCoO(2) system. An in situ X-ray diffraction (XRD) thermal study emphasizes the metastable character of this phase that can be stabilized only by very fast quenching. Its composition, (Li(0.42)Na(0.37))CoO(2), is significantly different from the ideally expected one, (Li(0.50)Na(0.35))CoO(2), and its structure, confirmed by Rietveld refinement of the XRD pattern, presents an ideal alternate ordering of lithium, cobalt, and sodium layers within OP4-type oxygen packing. The presence of vacancies in both alkali-ion layers was confirmed by electrochemical intercalation of lithium and sodium. For the first time, a new type of layered oxide exhibiting OPP9-type oxygen packing was evidenced. Between the CoO(2) slabs, alkali ions are intercalated in the following order: Li(octa)-Na(prism)-Na(prism). This material crystallizes in the R3m space group with a(hex) = 2.828 A and c(hex) = 46.85 A cell parameters.
28 citations
TL;DR: In this article, the magnetic properties of LiFePO4·OH and FePO 4·H2O were investigated and the former showed no Curie-Weiss-type behavior up to room temperature, while the latter tends to s...
Abstract: 7Li, 31P, and 1H MAS NMR spectra and magnetic properties are reported for LiFePO4·OH and FePO4·H2O. The former shows no Curie–Weiss-type behavior up to room temperature, while the latter tends to s...
26 citations
TL;DR: The metastable 1:1 Li/Na-stacked OP4-Li0.42Na0.37CoO2 phase was synthesized from a mixture of O3-LiCoO 2 and P2-Na 0.7 CoO 2 in a molar ratio of 42:58 as mentioned in this paper.
Abstract: The metastable 1:1 Li/Na-stacked OP4-Li0.42Na0.37CoO2 phase is synthesized from a mixture of O3-LiCoO2 and P2-Na0.7CoO2 in a molar ratio of 42:58 (sealed gold tubes, 920 °C, 24 h, very fast quenching).
7 citations
TL;DR: In this article, a sol-gel method was used to synthesize LixNa1-xMnFe2(PO4)3 from stoichiometric amounts of Na2CO3, Li 2CO3 and MnCO3 in H2O containing HNO3 and citric acid (800 °C, 30 min).
Abstract: LixNa1-xMnFe2(PO4)3 (x = 0, 0.5, 0.75) is synthesized by a sol—gel method from stoichiometric amounts of Na2CO3, Li2CO3, MnCO3, FeC2O4, and (NH4)H2PO4 in H2O containing HNO3 and citric acid (800 °C, 30 min).
6 citations