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Janna K. Maranas - One of the best experts on this subject based on the ideXlab platform.
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A molecular dynamics study of the structural dependence of Boron Oxide nanoparticles on shape
Nano letters, 2005Co-Authors: Susan Fullerton, Janna K. MaranasAbstract:Molecular dynamics simulation is employed to study the effect of varying nanoparticle shape on the structure of Boron Oxide nanoparticles. Two nanoshapes are investigated and compared: a sphere of diameter 16 A and a cube of dimension 16 x 16 x 16 A. A many-body polarization model is employed within the simulation, accounting for dipole moments induced by local electric fields. The resulting network is described by a short-range structure consisting of planar BO(3) units, while the intermediate-range structure is described by six-membered planar boroxol rings. Both the fraction of boroxol rings and their locations differ between the two nanoshapes. All planar boroxol rings within the spherical simulation are located on the interior, while planar rings within the cubic simulation aggregate to the cube walls. In addition, structural differences appear between the two shapes at longer ranges, including the formation of "layers" aligned parallel to the walls of the cube, reminiscent of both the low-density crystalline phase and the high-density amorphous form of Boron Oxide.
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A molecular interpretation of vitreous Boron Oxide dynamics
Journal of Chemical Physics, 2004Co-Authors: Susan Fullerton, Janna K. MaranasAbstract:The mobility of vitreous Boron Oxide is studied by molecular dynamics simulation. A polarization model that incorporates induced dipoles arising both from charges and from other induced dipoles on atoms with nonzero polarizability is used to simulate Boron Oxide glass at various temperatures above the glass transition temperature. Particle mobility is investigated through the calculation of the self-intermediate scattering function and the mean-squared displacement. The calculations clearly reveal a two-step relaxation with a plateau at intermediate times for all investigated temperatures. With respect to atomic species, Boron atoms are less mobile than oxygen atoms at all temperatures within the plateau region. Through analyzing particle trajectories, it is revealed that BO3 groups move as one unit and follow each other in a stringlike manner. Three connected BO3 groups comprise a six-membered boroxol ring, which is shown to move in a collective manner, requiring the simultaneous movement of all ring ato...
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Polarization interactions and boroxol ring formation in Boron Oxide: A molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Janna K. Maranas, Yingzi Chen, Dorothea K. Stillinger, Frank H. StillingerAbstract:We employ molecular dynamics (MD) simulations to study the structure of vitreous Boron Oxide. Although six-membered boroxol rings have been observed at fractions over 60% by various experimental techniques, simulation methods have not produced similar results. We adapt the polarization model, which includes many body polarization effects thought to stabilize such structures, for Boron–oxygen interactions. This model is then used in MD simulations of Boron Oxide glass at various temperatures. We find a variation in the fraction of rings depending on the temperature of the system during network formation. The maximum ring fraction (∼33%) occurs when the sample is prepared at low temperatures. At these temperatures, the energy level of Boron atoms in rings is 1.6% lower than the energies of Boron atoms outside of rings. When higher equilibration temperatures are used, the fraction drops to 11%. Thus, two factors are relevant to boroxol ring formation in simulations of Boron Oxide, a model which incorporates ...
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Polarization interactions and boroxol ring formation in Boron Oxide: A molecular dynamics study
The Journal of Chemical Physics, 2001Co-Authors: Janna K. Maranas, Yingzi Chen, Dorothea K. Stillinger, Frank H. StillingerAbstract:We employ molecular dynamics (MD) simulations to study the structure of vitreous Boron Oxide. Although six-membered boroxol rings have been observed at fractions over 60% by various experimental techniques, simulation methods have not produced similar results. We adapt the polarization model, which includes many body polarization effects thought to stabilize such structures, for Boron–oxygen interactions. This model is then used in MD simulations of Boron Oxide glass at various temperatures. We find a variation in the fraction of rings depending on the temperature of the system during network formation. The maximum ring fraction (∼33%) occurs when the sample is prepared at low temperatures. At these temperatures, the energy level of Boron atoms in rings is 1.6% lower than the energies of Boron atoms outside of rings. When higher equilibration temperatures are used, the fraction drops to 11%. Thus, two factors are relevant to boroxol ring formation in simulations of Boron Oxide, a model which incorporates polarization effects or their equivalent, and the appropriate manipulation of temperature history.
Frank H. Stillinger - One of the best experts on this subject based on the ideXlab platform.
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Polarization interactions and boroxol ring formation in Boron Oxide: A molecular dynamics study
Journal of Chemical Physics, 2001Co-Authors: Janna K. Maranas, Yingzi Chen, Dorothea K. Stillinger, Frank H. StillingerAbstract:We employ molecular dynamics (MD) simulations to study the structure of vitreous Boron Oxide. Although six-membered boroxol rings have been observed at fractions over 60% by various experimental techniques, simulation methods have not produced similar results. We adapt the polarization model, which includes many body polarization effects thought to stabilize such structures, for Boron–oxygen interactions. This model is then used in MD simulations of Boron Oxide glass at various temperatures. We find a variation in the fraction of rings depending on the temperature of the system during network formation. The maximum ring fraction (∼33%) occurs when the sample is prepared at low temperatures. At these temperatures, the energy level of Boron atoms in rings is 1.6% lower than the energies of Boron atoms outside of rings. When higher equilibration temperatures are used, the fraction drops to 11%. Thus, two factors are relevant to boroxol ring formation in simulations of Boron Oxide, a model which incorporates ...
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Polarization interactions and boroxol ring formation in Boron Oxide: A molecular dynamics study
The Journal of Chemical Physics, 2001Co-Authors: Janna K. Maranas, Yingzi Chen, Dorothea K. Stillinger, Frank H. StillingerAbstract:We employ molecular dynamics (MD) simulations to study the structure of vitreous Boron Oxide. Although six-membered boroxol rings have been observed at fractions over 60% by various experimental techniques, simulation methods have not produced similar results. We adapt the polarization model, which includes many body polarization effects thought to stabilize such structures, for Boron–oxygen interactions. This model is then used in MD simulations of Boron Oxide glass at various temperatures. We find a variation in the fraction of rings depending on the temperature of the system during network formation. The maximum ring fraction (∼33%) occurs when the sample is prepared at low temperatures. At these temperatures, the energy level of Boron atoms in rings is 1.6% lower than the energies of Boron atoms outside of rings. When higher equilibration temperatures are used, the fraction drops to 11%. Thus, two factors are relevant to boroxol ring formation in simulations of Boron Oxide, a model which incorporates polarization effects or their equivalent, and the appropriate manipulation of temperature history.
Susan Fullerton - One of the best experts on this subject based on the ideXlab platform.
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A molecular dynamics study of the structural dependence of Boron Oxide nanoparticles on shape
Nano letters, 2005Co-Authors: Susan Fullerton, Janna K. MaranasAbstract:Molecular dynamics simulation is employed to study the effect of varying nanoparticle shape on the structure of Boron Oxide nanoparticles. Two nanoshapes are investigated and compared: a sphere of diameter 16 A and a cube of dimension 16 x 16 x 16 A. A many-body polarization model is employed within the simulation, accounting for dipole moments induced by local electric fields. The resulting network is described by a short-range structure consisting of planar BO(3) units, while the intermediate-range structure is described by six-membered planar boroxol rings. Both the fraction of boroxol rings and their locations differ between the two nanoshapes. All planar boroxol rings within the spherical simulation are located on the interior, while planar rings within the cubic simulation aggregate to the cube walls. In addition, structural differences appear between the two shapes at longer ranges, including the formation of "layers" aligned parallel to the walls of the cube, reminiscent of both the low-density crystalline phase and the high-density amorphous form of Boron Oxide.
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A molecular interpretation of vitreous Boron Oxide dynamics
Journal of Chemical Physics, 2004Co-Authors: Susan Fullerton, Janna K. MaranasAbstract:The mobility of vitreous Boron Oxide is studied by molecular dynamics simulation. A polarization model that incorporates induced dipoles arising both from charges and from other induced dipoles on atoms with nonzero polarizability is used to simulate Boron Oxide glass at various temperatures above the glass transition temperature. Particle mobility is investigated through the calculation of the self-intermediate scattering function and the mean-squared displacement. The calculations clearly reveal a two-step relaxation with a plateau at intermediate times for all investigated temperatures. With respect to atomic species, Boron atoms are less mobile than oxygen atoms at all temperatures within the plateau region. Through analyzing particle trajectories, it is revealed that BO3 groups move as one unit and follow each other in a stringlike manner. Three connected BO3 groups comprise a six-membered boroxol ring, which is shown to move in a collective manner, requiring the simultaneous movement of all ring ato...
Dmitri Golberg - One of the best experts on this subject based on the ideXlab platform.
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Boron nitride nanotube growth via Boron Oxide assisted chemical vapor transport-deposition process using LiNO3 as a promoter
Nano Research, 2015Co-Authors: A. T. Matveev, Konstantin L. Firestein, Alexander E. Steinman, Andrey M. Kovalskii, Oleg I. Lebedev, Dmitry V. Shtansky, Dmitri GolbergAbstract:High-purity straight and discrete multiwalled Boron nitride nanotubes (BNNTs) were grown via a Boron Oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of Boron Oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray (EDX) and Raman spectroscopies. Boron Oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 °C, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30–50 nm were mostly observed in a temperature range of 1,280–1,320 °C. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 °C, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.
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Boron nitride nanotube growth via Boron Oxide assisted chemical vapor transport-deposition process using LiNO 3 as a promoter
Nano Research, 2015Co-Authors: A. T. Matveev, Konstantin L. Firestein, Alexander E. Steinman, Andrey M. Kovalskii, Oleg I. Lebedev, Dmitry V. Shtansky, Dmitri GolbergAbstract:High-purity straight and discrete multiwalled Boron nitride nanotubes (BNNTs) were grown via a Boron Oxide vapor reaction with ammonia using LiNO 3 as a promoter. Only a trace amount of Boron Oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray (EDX) and Raman spectroscopies. Boron Oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 °C, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30–50 nm were mostly observed in a temperature range of 1,280–1,320 °C. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 °C, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed. [Figure not available see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
Alfredo Pasquarello - One of the best experts on this subject based on the ideXlab platform.
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Fraction of boroxol rings in vitreous Boron Oxide from a first-principles analysis of Raman and NMR spectra
Physical Review Letters, 2005Co-Authors: Paolo Umari, Alfredo PasquarelloAbstract:We determine the fraction f of B atoms belonging to boroxol rings in vitreous Boron Oxide through a first-principles analysis. After generating a model structure of vitreous B2O3 by first-principles molecular dynamics, we address a large set of properties, including the neutron structure factor, the neutron density of vibrational states, the infrared spectra, the Raman spectra, and the B-11 NMR spectra, and find overall good agreement with corresponding experimental data. From the analysis of Raman and B-11 NMR spectra, we yield consistently for both probes a fraction f of similar to 0.75. This result indicates that the structure of vitreous Boron Oxide is largely dominated by boroxol rings.