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Gregory J. Lewis - One of the best experts on this subject based on the ideXlab platform.
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Zeolite Synthesis from a Charge Density Perspective: The Charge Density Mismatch Synthesis of UZM-5 and UZM-9
Chemistry of Materials, 2014Co-Authors: Min Bum Park, Him Chan Jeon, Christopher P. Nicholas, Gregory J. Lewis, Suk Bong HongAbstract:A Charge Density model of aluminosilicate zeolite synthesis is presented. This model has been applied to the Charge Density mismatch (CDM) synthesis of UZM-5 and UZM-9 zeolites at 150 and 100 °C, respectively, using the same synthesis mixture that includes tetraethylammonium (TEA+), tetramethylammonium (TMA+), and Na+ ions as structure-directing agents (SDAs). It allows a seamless description of the contributions of both the hydroxide and SDA components of the CDM barrier to zeolite synthesis. The syntheses are described as temperature-driven confrontations with the CDM barrier, resulting in disproportionation to solution and solid products with diverging Charge densities. The presence of the CDM barrier and this tunable disproportionation in Charge Density, along with the suitable choice of SDA concentrations, allows a flexible and cooperative participation of SDAs, as the synthesis medium initially forms aluminosilicate networks that maximize Coulombic stabilization under the conditions at hand. The UZM...
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Experimental Charge Density matching approach to zeolite synthesis
Studies in Surface Science and Catalysis, 2004Co-Authors: Gregory J. Lewis, Mark A. Miller, Jamie G. Moscoso, Ben A. Wilson, Lisa M. Knight, Stephen T. WilsonAbstract:Abstract An Experimental Charge Density Matching (ECDM) approach to zeolite synthesis is described. The method features the initial formation of a Charge Density Mismatch (CDM) aluminosilicate reaction mixture characterized by the mismatch between the Charge Density on the organoammonium structure directing agent (SDA) and the Charge Density on the potential aluminosilicate network that is expected to form. This amounts to creating an aluminosilicate reaction mixture using a large SDA and a low Si/A1 ratio, but also depends on hydroxide levels and crystallization temperature. The crystallization of a zeolite from such a reaction mixture may be difficult, or even impossible. Crystallization can be induced by the controlled addition of supplemental SDA's that have Charge densities that are more suitably matched to that of the desired low ratio aluminosilicate network. Advantages of this approach are greater control over the crystallization process and reliable cooperation of multiple templates. The approach is demonstrated in the TEA-TMA template system, in which the new zeolites UZM-4, UZM-5, and UZM-9 are synthesized.
Suk Bong Hong - One of the best experts on this subject based on the ideXlab platform.
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Zeolite Synthesis from a Charge Density Perspective: The Charge Density Mismatch Synthesis of UZM-5 and UZM-9
Chemistry of Materials, 2014Co-Authors: Min Bum Park, Him Chan Jeon, Christopher P. Nicholas, Gregory J. Lewis, Suk Bong HongAbstract:A Charge Density model of aluminosilicate zeolite synthesis is presented. This model has been applied to the Charge Density mismatch (CDM) synthesis of UZM-5 and UZM-9 zeolites at 150 and 100 °C, respectively, using the same synthesis mixture that includes tetraethylammonium (TEA+), tetramethylammonium (TMA+), and Na+ ions as structure-directing agents (SDAs). It allows a seamless description of the contributions of both the hydroxide and SDA components of the CDM barrier to zeolite synthesis. The syntheses are described as temperature-driven confrontations with the CDM barrier, resulting in disproportionation to solution and solid products with diverging Charge densities. The presence of the CDM barrier and this tunable disproportionation in Charge Density, along with the suitable choice of SDA concentrations, allows a flexible and cooperative participation of SDAs, as the synthesis medium initially forms aluminosilicate networks that maximize Coulombic stabilization under the conditions at hand. The UZM...
Ettore Vicari - One of the best experts on this subject based on the ideXlab platform.
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Improved lattice operators: Case of the topological Charge Density.
Physical Review D, 1996Co-Authors: Chariton Christou, Adriano Di Giacomo, Haralambos Panagopoulos, Ettore VicariAbstract:We analyze the properties of a class of improved lattice topological Charge Density operators, constructed by a smearinglike procedure. By optimizing the choice of the parameters introduced in their definition we find operators having (i) a better statistical behavior as estimators of the topological Charge Density on the lattice, i.e., less noisy, (ii) a multiplicative renormalization much closer to one, and (iii) a large suppression of the perturbative tail (and other unphysical mixings) in the corresponding lattice topological susceptibility. {copyright} {ital 1996 The American Physical Society.}
Marie-aude Méasson - One of the best experts on this subject based on the ideXlab platform.
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Higgs-mode radiance and Charge-Density-wave order in 2H−NbSe2
Physical Review B: Condensed Matter and Materials Physics, 2018Co-Authors: Romain Grasset, Tommaso Cea, Yann Gallais, Maximilien Cazayous, Alain Sacuto, Laurent Cario, Lara Benfatto, Marie-aude MéassonAbstract:Despite being usually considered two competing phenomena, Charge-Density wave and superconductivity coexist in few systems, the most emblematic one being the transition-metal dichalcogenide $H$ − NbSe$_2$ . This unusual condition is responsible for specific Raman signatures across the two phase transitions in this compound. While the appearance of a soft phonon mode is a well-established fingerprint of the Charge-Density-wave order, the nature of the sharp subgap mode emerging below the superconducting temperature is still under debate. In this work we use external pressure as a knob to unveil the delicate interplay between the two orders, and consequently the nature of the superconducting mode. Thanks to an advanced extreme-conditions Raman technique, we are able to follow the pressure evolution and the simultaneous collapse of the two intertwined Charge-Density-wave and superconducting modes. The comparison with microscopic calculations in a model system supports the Higgs-type nature of the superconducting mode and suggests that Charge-Density wave and superconductivity in $H$ − NbSe$_2$ involve mutual electronic degrees of freedom. These findings fill the knowledge gap on the electronic mechanisms at play in transition-metal dichalcogenides, a crucial step to fully exploit their properties in few-layer systems optimized for device applications.
Gerrit E W Bauer - One of the best experts on this subject based on the ideXlab platform.
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Strong effects of weak localization in Charge-Density-wave/normal-metal hybrids
Physical Review B, 2000Co-Authors: Mark I. Visscher, Behzad Rejaei, Gerrit E W BauerAbstract:Collective transport through a multichannel disordered conductor in contact with Charge-Density-wave electrodes is theoretically investigated. The statistical distribution function of the threshold potential for Charge-Density wave sliding is calculated by random matrix theory. In the diffusive regime weak localization has a strong effect on the sliding motion.
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Charge Density wave ratchet
Applied Physics Letters, 1999Co-Authors: Mark I. Visscher, Gerrit E W BauerAbstract:We propose to operate a locally gated Charge Density wave as an electron pump. Applying an oscillating gate potential with frequency f causes equally spaced plateaus in the sliding Charge Density wave current separated by ΔI=2eNf, where N is the number of parallel chains. The effects of thermal noise are investigated.