Anh Phạm Quốc Nghị, ĐH KHTN Hà Nội, đã lấy bằng PhD tại Université du Maine, France, hiện anh Nghị đang làm postdoc tại INPL-Nancy, France. Anh Nghị ủng hộ PhD Thesis và 9 bài báo của anh ấy cho thư viện ChemVN. BM cho các bài báo vào folder Hóa Vô cơ nhé.
PhD Thesis: Elaboration et caractérisation d'oxydes perovskites pour capteurs de pH - Etude du mécanisme de fonctionnement de ces capteurs
Author: Quoc Nghi PHAM
Université du Maine, France Issue date: September 2006
Các bài báo trên tạp chí quốc tế:
1, Influence of the gelator structure and solvent on the organisation and chirality of self-assembling fibrillar networks
New J. Chem., 2008
Quoc Nghi Pham, Nicolas Brosse, Céline Frochot, Dominique Dumas, Alexandre Hocquet and Brigitte Jamart-Grégoire
Abstract: Chromophoric probes of naphthalimide moieties enable evaluation of their assembling behaviour photophysically through fluorescence spectroscopy and microscopy, and circular dichroism. These experiments highlight the influence of the nature of the chemical substitution of the organogelator. Very interesting results were also obtained by performing CD experiments showing that the nature of the solvent should modify the chirality of self-assembled aggregates. Highly oriented network structures were observed in the gel state and disappeared in isotropic solution. Microfibrous self-aggregation of organogels is in situ observed via fluorescence and SHG imaging and confirmed by transmission electron microscopic analysis of the dried sample.
2, Synthesis and Characterization of Nanostructured Fast Ionic Conductor Li0.30La0.56TiO3
Chem. Mater., 18 (18), 4385 -4392, 2006
Quoc Nghi Pham, Claude Bohnké, Marie-Pierre Crosnier-Lopez, and Odile Bohnké
Abstract:
The preparation of a pure and nanostructured phase of the fast lithium conductor Li0.30La0.56TiO3 at low temperature (350 C for 2 h) is reported for the first time. The synthesis has been carried out by the Pechini-type in-situ polymerizable method. It has been shown that the molar ratios ethylene glycol/citric acid and citric acid/metals, as well as the temperature, are crucial parameters during this synthesis. A careful control of the temperature during polyesterification allowed us to prepare the nanosized phase of oxide and to avoid the formation of thermally stable impurities. The crystallite size (20-30 nm) of the oxide has been determined by the analysis of the broadening of the powder X-ray diffraction lines. The particles size has been confirmed by transmission electron microscopy and the macroporous character of the powder has been evidenced by scanning electron microscopy.
3, Synthesis of the perovskite ceramic Li3xLa2/3–xTiO3 by a chemical solution route using a triblock copolymer surfactant
Journal of Sol-Gel Science and Technology, Volume 46, Number 2 / May, 2008, 137-145
Thi Ngoc Ha Le, Mickaël Roffat, Quoc Nghi Pham, Stéphanie Kodjikian, Odile Bohnke and Claude Bohnke
Abstract: The synthesis of the perovskite Li3xLa2/3–x□1/3–2xTiO3 by a chemical solution route, using a triblock copolymer surfactant, PEOn–PPOm–PEOn, is described. This titanate is a non-hygroscopic fast lithium conductor and therefore is a good candidate for electrochemical applications. It is generally prepared by a conventional solid-state reaction (SSR) method. However this synthesis method does not allow the preparation of nanopowders or the formation of thin films. For these special purposes, synthesis by a chemical solution route, with the formation of a polymeric precursor during synthesis, has been investigated. By using the above-mentioned non-ionic surfactant, the preparation of nanopowders of complex oxides can be done. Furthermore, this way of synthesis leads to the formation of an intermediate polymeric precursor which can be easily spread on substrates to obtain films. We show that the formation of a pure phase of the perovskite Li3xLa2/3–x□1/3–2xTiO3 is highly dependent on the synthesis conditions, namely the presence of water in the solvent, the EO/metal ratio, the Li+ content in the precursor and the calcination temperature. The influence of these parameters on the microstructure of the oxide is studied by X-ray diffraction, scanning electron microscopy and granulometry. A powder of Li3xLa2/3–x□1/3–2xTiO3 (x = 0.10), with an average particles size of 200 nm, has been obtained. The ionic conductivity of this oxide is the same as the one obtained with oxide prepared by SSR (a bulk conductivity of 1.4 × 10−3 S/cm at 37 °C). The ceramic obtained from this powder after sintering at 1,150 °C shows a good pH response. This material can then be used as a sensitive membrane in a potentiometric pH sensor. The presence of hydrophobic PPO groups in the polymer precursor allowed preparing films of Li3xLa2/3–x□1/3–2xTiO3 with a good adherence on Pt substrate. This kind of synthesis is then very promising to prepare micro pH sensors.
4, Potentiometric measurements and impedance characteristics of Li0.30La0.57TiO3 membrane in lithium anhydrous solutions
The potentiometric response of the Li+ ion-selective electrode based on the fast ion conductor Li3xLa2/3−xTiO3 (x = 0.10) membrane (named LLTO) as well as the impedance of the LLTO membrane/Li+ solution in either anhydrous or hydrated PC solvent have been carried out. A four-electrode configuration has been used for the investigation of the interfacial phenomenon. It has been shown that the LLTO membrane can be used to detect the Li+ activity in anhydrous solutions through a Li+ ion exchange mechanism. The potentiometric response shows a Nernstian behavior with a Li+ sensitivity of −72 mV/decade at 25 °C. This high sensitivity can be correlated to a localised hydroxylation of the oxide surface with the residual water present in the solution in combination to the Li+ exchange reaction. An apparent standard current density of 12 μA/cm2 and a charge-transfer coefficient of 0.29 have been determined. However, as water content in the electrolyte increases, the activity domain of the detection decreases to lead to the disappearance of the Li+ ion exchange mechanism in Li+ aqueous solution. This annihilation of the exchange process may be due to the predominant catalytic reaction of [Ti–O]− with H2O and/or to the formation of a water layer on the oxide surface.
5, Synthesis and electrical characterization of Li0.30Ca0.35TaO3 perovskite synthesized via a polymerized complex route
Journal of Solid State Chemistry, Volume 178, Issue 6, June 2005, Pages 1915-1924
Quoc Nghi Pham, Murugesan Vijayakumar, Claude Bohnke, Odile Bohnke
Abstract
The synthesis of Li0.30Ca0.35TaO3 perovskite by a Pechini-type polymerizable precursor method is carefully described. The thermal decomposition of the precursor and the formation of a pure perovskite phase were investigated by means of differential thermal analysis–thermogravimetric analysis (DTA–TGA) and XRD techniques. A pure and well-crystallized phase has been obtained at a lower temperature and with a much shorter synthesis time than the phase obtained by conventional solid-state reaction method. The morphology of the powder after heating at 1300 °C was observed by laser granulometry, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Impedance spectroscopy data allowed us to determine the electrical properties, i.e., permittivity and dc-conductivity, of the bulk and grain boundaries. The results are discussed on the assumption of the brick layer model.
6, A new perovskite phase Li2xCa0.5−xTaO3: Li+ ion conductivity and use as pH sensor
Solid State Ionics, Volume 176, Issues 5-6, 14 February 2005, Pages 495-504
Quoc Nghi Pham, Claude Bohnke, Joël Emery, Odile Bohnke, Françoise Le Berre, Marie-Pierre Crosnier-Lopez, Jean-Louis Fourquet, Pierre Florian
Abstract
Several compounds of a new solid solution Li2xCa0.5−xTaO3 (0.05≤x≤0.25) with perovskite structure have been synthesised by classical solid state reaction. It has been found that synthesis at 1773 K followed by a quenching in air was necessary to obtain a pure perovskite phase. The cell parameters and their variation with composition x have been determined through X-ray diffraction patterns analysis. Scanning electron microscopy showed the presence of grains of 10 μm size and of aggregates of 50–100 μm thick. Impedance spectroscopy in the frequency range from 10 MHz to 1 Hz and in the temperature range from 348 to 573 K has been carried out to determine the electrical properties. A bulk dc-conductivity slightly higher than 10−6 S cm−1 has been found at 473 K. 7Li nuclear magnetic resonance relaxation times, T1 and T1ρ, vs. inverse of temperature have been measured to investigate the microscopic ionic motions of Li+ ions. Two motions of Li+ ions, a short and a long range one, are evidenced by these experiments. Furthermore, the Galvani potential of the ionic conductive membrane electrode, when put in contact with an aqueous solution, depends on the pH of the solution. The fast response on pH variation enables it then to be used as pH sensor in aqueous solutions.
7, Lithium lanthanum titanate ceramic as sensitive material for pH sensor: Influence of synthesis methods and powder grains size
Journal of the European Ceramic Society, Volume 25, Issue 12, 2005, Pages 2973-2976
Murugesan Vijayakumar, Quoc Nghi Pham, Claude Bohnke
Abstract
The lithium lanthanum titanate (LLTO), prepared by two different methods (solid state reaction and sol–gel), has been studied as sensitive element for detecting the pH variations in aqueous solutions when used as a potentiometric sensor. This property is dependent on mechanical and thermal treatments of the synthesised powder. A screening design was performed with the material obtained by solid state reaction. Several parameters (grinding time, heating rate for sintering process…) have been optimized. The main step, which increases the sensitivity, is the grinding of the powder before a heat treatment when the LLTO is synthesised by solid state reaction. We suppose that a small grains size of the powder is favourable to the pH variations sensitivity. A comparison with LLTO synthesised by the sol–gel route without grinding is also shown. The sensitivities of these two materials to the pH variations are very similar.
8, Effect of surface treatments on Li0.30Ln0.57TiO3 (Ln = La, Nd) perovskite ceramics: an X-ray photoelectron spectroscopy study
To explain the sensitivity of some titanate ceramics to pH variation in aqueous solutions, the lithium lanthanum titanate (LLTO) and lithium neodymium titanate (NLTO) surfaces were analysed by X-ray photoelectron spectroscopy. The surface of LLTO was modified by chemical treatments and sputtering. XPS spectrum of LLTO exhibits the peaks of lanthanum (La 3d3/2, La 3d5/2, La 4p, La 4d), titanium (Ti 2p1/2, Ti 2p3/2) and oxygen (O 1s). However, the immersion of the ceramic in sodium hydroxide or surface sputtering affect mainly the narrow-scan spectra of oxygen (O 1s). This study reveals that an acido-basic reaction takes place in the neighbourhood of the TiO6 octahedra of the perovskite. The results also suggest that hydroxyl species may associate with lanthanum. Furthermore, the study on C 1s line rules out the assumption that View the MathML source species are involved in the pH detection.
9, Crystal structure of new Li+ ion conducting perovskites: Li2xCa0.5−xTaO3 and Li0.2[Ca1−ySry]0.4TaO3
Solid State Sciences, Volume 6, Issue 9, September 2004, Pages 923-929
Quoc Nghi Pham, Marie-Pierre Crosnier-Lopez, Françoise Le Berre, François Fauth, Jean-Louis Fourquet
Abstract
Two new solid solutions—Li2xCa0.5−xTaO3 (0.05<x<0.25) and Li0.2[Ca1−ySry]0.4TaO3 (0<y<0.15)—based on the A defective ABO3 perovskite structural type, are synthesized. The crystal structures of these Li+ ion conducting compounds are solved from synchrotron radiation and conventional X-ray powder diffraction data. The unit cells exhibit a classical orthorhombic distortion of the cubic perovskite model (space group Pnma No. 62) with parameters close to Image , 2ap, Image (ap, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a+b−b− of the TaO6 octahedra. For the same lithium content (x=0.10), the Sr2+ substitution to Ca2+ is found to enhance the electrical conductivity by quasi-one order of magnitude (at 200 °C, bulk dc conductivity values are close to 2.3×10−6 and 1.1×10−5 S cm−1 for Li0.2Ca0.4TaO3 and Li0.2[Ca0.9Sr0.1]0.4TaO3, respectively).
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