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John M Seddon - One of the best experts on this subject based on the ideXlab platform.
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hydrostatic pressure effects on a hydrated lipid inverse micellar Fd3m cubic phase
Physical Chemistry Chemical Physics, 2011Co-Authors: Arwen I I Tyler, R H Templer, Gemma C Shearman, Nicholas J Brooks, H Delacroix, Robert V Law, Oscar Ces, John M SeddonAbstract:Over a range of hydration, unsaturated diacylglycerol/phosphatidylcholine mixtures adopt an inverse micellar cubic phase, of crystallographic space group Fd3m. In this study hydrated DOPC:DOG mixtures with a molar ratio close to 1 ∶ 2 were examined as a function of hydrostatic pressure, using synchrotron X-ray diffraction. The small-angle diffraction pattern at atmospheric pressure was used to calculate 2-D sections through the electron density map. Pressure initially has very little effect on the structure of the Fd3m cubic phase, in contrast to its effect on hydrated inverse bicontinuous cubic phases. At close to 2 kbar, a sharp transition occurs from the Fd3m phase to a pair of coexisting phases, an inverse hexagonal HII phase plus an (ordered) lamellar phase. Upon increasing the pressure to 3 kbar, a further sharp transition occurs from the HII phase to a (fluid) lamellar phase, in coexistence with the ordered lamellar phase. These transitions are fully reversible, but show hysteresis. Remarkably, the lattice parameter of the Fd3m phase is practically independent of pressure. These results show that these two lipids are miscible at low pressure, adopting a single lyotropic phase (Fd3m); they then become immiscible above a critical pressure, phase separating into DOPC-rich and DOG-rich phases.
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an Fd3m lyotropic cubic phase in a binary glycolipid water system
Langmuir, 1996Co-Authors: John M Seddon, Neelofar Zeb, R H Templer, Ronald N Mcelhaney, David A MannockAbstract:The lyotropic cubic phase of space group Fd3m has been observed for the first time in a purely binary amphiphile/water system, consisting of fully-hydrated synthetic 1,2-di-O-alkyl-3-O-(α- or β-d-x...
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an inverse micellar Fd3m cubic phase formed by hydrated phosphatidylcholine fatty alcohol mixtures
Chemistry and Physics of Lipids, 1996Co-Authors: Zhi Huang, John M Seddon, R H TemplerAbstract:Abstract In this paper we report the observation of an inverse micellar cubic phase, of space group Fd3m, in fully hydrated diacyl phosphatidylcholine/fatty alcohol (PC/FAlc) symmetric mixtures, with each lipid component having the same chainlength. In the PC/FAlc systems described here, the Fd3m cubic phase is formed directly from the lamellar L β phase upon heating. All of the mixtures which form the Fd3m phase have an alcohol-rich composition, with the mol fractions of alcohol being in the region of 0.75–0.85. The Fd3m cubic phase occurs for PC/FAlc mixtures with chainlengths of C14, C16, C18 and C20. However, for the C14 mixture, the inverse hexagonal (H II ) phase coexists with the Fd3m cubic phase over an extensive temperature range, and only the H II phase is observed above the chain melting transition temperature for the C12 PC/FAlc mixture. Thus decreasing chain length tends to favour the formation of the H II phase over the Fd3m cubic phase. In the pseudo-binary phase diagrams of PC/FAlc mixtures in excess water, the Fd3m cubic phases appear between the H II phase and the inverse micellar solution phase (L 2 ). This is consistent with the average mean curvature of the polar/non-polar interface in the Fd3m cubic phase being more negative than that in the H II phase. The lattice parameters of these Fd3m phases show little temperature dependence. The lattice parameter increases steeply with hydrocarbon chain length at constant temperature (90°C) for chainlengths above C16, which implies that the limiting hydration of the Fd3m phase increases for these longer chainlengths.
Eric A Stach - One of the best experts on this subject based on the ideXlab platform.
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investigation of changes in the surface structure of lixni0 8co0 15al0 05o2 cathode materials induced by the initial charge
Chemistry of Materials, 2014Co-Authors: Sooyeon Hwang, Wonyoung Chang, Seung Min Kim, Donghyun Kim, Jeong Yong Lee, Kyung Yoon Chung, Eric A StachAbstract:We use transmission electron microscopy (TEM) to investigate the evolution of the surface structure of LixNi0.8Co0.15Al0.05O2 cathode materials (NCA) as a function of the extent of first charge at room temperature using a combination of high-resolution electron microscopy (HREM) imaging, selected area electron diffraction (SAED), and electron energy loss spectroscopy (EELS). It was found that the surface changes from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and eventually to the rock-salt structure (Fm3m), and that these changes are more substantial as the extent of charge increases. EELS indicates that these crystal structure changes are also accompanied by significant changes in the electronic structure, which are consistent with delithiation leading to both a reduction of the Ni and an increase in the effective electron density of oxygen. This leads to a charge imbalance, which results in the formation of oxygen vacancies and the development of surface poros...
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correlating structural changes and gas evolution during the thermal decomposition of charged lixni0 8co0 15al0 05o2 cathode materials
Chemistry of Materials, 2013Co-Authors: Seongmin Bak, Sooyeon Hwang, Wonyoung Chang, Kyung Yoon Chung, Eric A Stach, Kyungwan Nam, Kwangbum Kim, Xiaoqing YangAbstract:In this work, we present results from the application of a new in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy. We exploit this approach to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries. Results from charged LixNi0.8Co0.15Al0.05O2 cathode materials indicate that the evolution of both O2 and CO2 gases are strongly related to phase transitions that occur during thermal decomposition, specifically from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and finally to the rock-salt structure (Fm3m). The state of charge also significantly affects both the structural changes and the evolution of oxygen as the temperature increases: the more extensive the charge, the lower the temperature of the phase transitions and the larger the oxygen release. Ex situ X-ray absorption spectroscopy (XA...
R H Templer - One of the best experts on this subject based on the ideXlab platform.
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hydrostatic pressure effects on a hydrated lipid inverse micellar Fd3m cubic phase
Physical Chemistry Chemical Physics, 2011Co-Authors: Arwen I I Tyler, R H Templer, Gemma C Shearman, Nicholas J Brooks, H Delacroix, Robert V Law, Oscar Ces, John M SeddonAbstract:Over a range of hydration, unsaturated diacylglycerol/phosphatidylcholine mixtures adopt an inverse micellar cubic phase, of crystallographic space group Fd3m. In this study hydrated DOPC:DOG mixtures with a molar ratio close to 1 ∶ 2 were examined as a function of hydrostatic pressure, using synchrotron X-ray diffraction. The small-angle diffraction pattern at atmospheric pressure was used to calculate 2-D sections through the electron density map. Pressure initially has very little effect on the structure of the Fd3m cubic phase, in contrast to its effect on hydrated inverse bicontinuous cubic phases. At close to 2 kbar, a sharp transition occurs from the Fd3m phase to a pair of coexisting phases, an inverse hexagonal HII phase plus an (ordered) lamellar phase. Upon increasing the pressure to 3 kbar, a further sharp transition occurs from the HII phase to a (fluid) lamellar phase, in coexistence with the ordered lamellar phase. These transitions are fully reversible, but show hysteresis. Remarkably, the lattice parameter of the Fd3m phase is practically independent of pressure. These results show that these two lipids are miscible at low pressure, adopting a single lyotropic phase (Fd3m); they then become immiscible above a critical pressure, phase separating into DOPC-rich and DOG-rich phases.
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an inverse micellar Fd3m cubic phase formed by hydrated phosphatidylcholine fatty alcohol mixtures
Chemistry and Physics of Lipids, 1996Co-Authors: Zhi Huang, John M Seddon, R H TemplerAbstract:Abstract In this paper we report the observation of an inverse micellar cubic phase, of space group Fd3m, in fully hydrated diacyl phosphatidylcholine/fatty alcohol (PC/FAlc) symmetric mixtures, with each lipid component having the same chainlength. In the PC/FAlc systems described here, the Fd3m cubic phase is formed directly from the lamellar L β phase upon heating. All of the mixtures which form the Fd3m phase have an alcohol-rich composition, with the mol fractions of alcohol being in the region of 0.75–0.85. The Fd3m cubic phase occurs for PC/FAlc mixtures with chainlengths of C14, C16, C18 and C20. However, for the C14 mixture, the inverse hexagonal (H II ) phase coexists with the Fd3m cubic phase over an extensive temperature range, and only the H II phase is observed above the chain melting transition temperature for the C12 PC/FAlc mixture. Thus decreasing chain length tends to favour the formation of the H II phase over the Fd3m cubic phase. In the pseudo-binary phase diagrams of PC/FAlc mixtures in excess water, the Fd3m cubic phases appear between the H II phase and the inverse micellar solution phase (L 2 ). This is consistent with the average mean curvature of the polar/non-polar interface in the Fd3m cubic phase being more negative than that in the H II phase. The lattice parameters of these Fd3m phases show little temperature dependence. The lattice parameter increases steeply with hydrocarbon chain length at constant temperature (90°C) for chainlengths above C16, which implies that the limiting hydration of the Fd3m phase increases for these longer chainlengths.
Sooyeon Hwang - One of the best experts on this subject based on the ideXlab platform.
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investigation of changes in the surface structure of lixni0 8co0 15al0 05o2 cathode materials induced by the initial charge
Chemistry of Materials, 2014Co-Authors: Sooyeon Hwang, Wonyoung Chang, Seung Min Kim, Donghyun Kim, Jeong Yong Lee, Kyung Yoon Chung, Eric A StachAbstract:We use transmission electron microscopy (TEM) to investigate the evolution of the surface structure of LixNi0.8Co0.15Al0.05O2 cathode materials (NCA) as a function of the extent of first charge at room temperature using a combination of high-resolution electron microscopy (HREM) imaging, selected area electron diffraction (SAED), and electron energy loss spectroscopy (EELS). It was found that the surface changes from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and eventually to the rock-salt structure (Fm3m), and that these changes are more substantial as the extent of charge increases. EELS indicates that these crystal structure changes are also accompanied by significant changes in the electronic structure, which are consistent with delithiation leading to both a reduction of the Ni and an increase in the effective electron density of oxygen. This leads to a charge imbalance, which results in the formation of oxygen vacancies and the development of surface poros...
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correlating structural changes and gas evolution during the thermal decomposition of charged lixni0 8co0 15al0 05o2 cathode materials
Chemistry of Materials, 2013Co-Authors: Seongmin Bak, Sooyeon Hwang, Wonyoung Chang, Kyung Yoon Chung, Eric A Stach, Kyungwan Nam, Kwangbum Kim, Xiaoqing YangAbstract:In this work, we present results from the application of a new in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy. We exploit this approach to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries. Results from charged LixNi0.8Co0.15Al0.05O2 cathode materials indicate that the evolution of both O2 and CO2 gases are strongly related to phase transitions that occur during thermal decomposition, specifically from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and finally to the rock-salt structure (Fm3m). The state of charge also significantly affects both the structural changes and the evolution of oxygen as the temperature increases: the more extensive the charge, the lower the temperature of the phase transitions and the larger the oxygen release. Ex situ X-ray absorption spectroscopy (XA...
Yangkook Sun - One of the best experts on this subject based on the ideXlab platform.
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lini0 5mn1 5 o 4 showing reversible phase transition on 3 v region
Electrochemical and Solid State Letters, 2005Co-Authors: Sang Ho Park, Chongseung Yoon, Seungtaek Myung, Yangkook SunAbstract:Spinel LiNi 0 . 5 Mn 1 . 5 O 4 powders with different space group of Fd3m and P4 3 32 were synthesized by an ultrasonic spray pyrolysis method. The morphologies of the prepared powders depended on their structures; polyhedral shape for Fd3m and octahedral for P4 3 32. The obtained discharge capacities of the Fd3m and P4 3 32 were about 60 mAh g - 1 and 70 mAh g - 1 , respectively. Structural changes of both compounds were investigated on 3 V region by ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). From the ex situ XRD and HRTEM studies, LiNi 0 . 5 Mn 1 . 5 O 4 having P4 3 32 symmetry showed that structural transition occurred reversibly from simple cubic (P4 3 32) to tetragonal phase (I4 1 /amd), whereas irreversible structural changes were observed for Fd3m symmetry on 3V region.
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phase transitions in li1 δ ni0 5mn1 5 o 4 during cycling at 5 v
Electrochemical and Solid State Letters, 2004Co-Authors: Junghyun Kim, Chongseung Yoon, Seungtaek Myung, Jai Prakash, Yangkook SunAbstract:Structural change of LiNi 0 . 5 Mn 1 . 5 O 4 with two different crystallographic structures of Fd3m and P4 3 32 was studied during Li extraction. Ex situ X-ray diffraction and transmission electron microscopy studies on partially delithiated Li 1 - δ Ni 0 . 5 Mn 1 . 5 O 4 revealed that LiNi 0 . 5 Mn 1 . 5 O 4 (Fd3m) structure lost its characteristic diagonal glide symmetry, suggesting a structural transition arising from the possible migration of cations during oxidation from Ni 2 + to Ni 4 + . For the Li 1 - δ Ni 0 . 5 Mn 1 . 5 O 4 (P4 3 32), ordering of cations was destroyed by random migration of cations during Li extraction, resulting in the formation of intermediate phase with the Fd3m structure. The phase transitions were reversible, meaning that migration of cations is highly reversible during lithiation/delithiation.
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comparative study of lini0 5mn1 5o4 δ and lini0 5mn1 5o4 cathodes having two crystallographic structures Fd3m and p4332
Chemistry of Materials, 2004Co-Authors: Junghyun Kim, Chongseung Yoon, Seungtaek Myung, Sung Goon Kang, Yangkook SunAbstract:Nonstoichiometric LiNi0.5Mn1.5O4-δ and stoichiometric LiNi0.5Mn1.5O4 cathodes with two different structures (Fd3m and P4332) were synthesized by a molten salt method. Rietveld refinement of the X-ray diffraction (XRD) data and a selected-area electron diffraction (SAED) study confirmed that the face-centered spinel (Fd3m) transformed to the primitive simple cubic (P4332) upon additional heating at 700 °C. The LiNi0.5Mn1.5O4-δ cathode having the space group of Fd3m showed better electrochemical behaviors than did the LiNi0.5Mn1.5O4 cathode with the space group of P4332, specifically, a lower area-specific impedance (ASI) and a higher discharge capacity during cycling at high rate. XRD and SAED showed that both stoichiometric and nonstoichiometric LiNi0.5Mn1.5O4-δ exhibited similar SAED patterns with extra 002 spots at the fully delithiated state, suggesting a structural transition arising from the possible migration of transition metal cations during Li extraction. In addition, stoichiometric LiNi0.5Mn1...
