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Reizo Kato - One of the best experts on this subject based on the ideXlab platform.
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high pressure Crystal structure and electrical properties of a single component Molecular Crystal ni dddt 2 dddt 5 6 dihydro 1 4 dithiin 2 3 dithiolate
Molecules, 2019Co-Authors: Hengbo Cui, Takao Tsumuraya, Hamish H.-m. Yeung, Chloe S. Coates, Mark R. Warren, Reizo KatoAbstract:Single-component Molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and Crystal structure of the single-component Crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component Molecular Crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single Crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and interMolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined Crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures.
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High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)
MDPI AG, 2019Co-Authors: Hengbo Cui, Takao Tsumuraya, Hamish H.-m. Yeung, Chloe S. Coates, Mark R. Warren, Reizo KatoAbstract:Single-component Molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and Crystal structure of the single-component Crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component Molecular Crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single Crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and interMolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined Crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures
Thomas D Sewell - One of the best experts on this subject based on the ideXlab platform.
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nanoindentation of the triclinic Molecular Crystal 1 3 5 triamino 2 4 6 trinitrobenzene a Molecular dynamics study
Journal of Physical Chemistry C, 2016Co-Authors: Nithin Mathew, Thomas D SewellAbstract:Nanoindentation of the insensitive energetic Molecular Crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) was studied using constant-temperature and constant-energy Molecular dynamics simulations. Displacement-controlled indentations at constant velocity were performed using a rigid, spherical indenter on the three principal Crystallographic planes, (100), (010), and (001). The force–displacement curve for the (001) (basal) plane exhibits a distinct elastic region in agreement with the analytical solution for indentation of an anisotropic half-space by a parabola of revolution. Stiffening precedes inelastic deformation, and the elastic–inelastic transition occurs with kinking and delamination of the layered basal planes and significant pile-up. The predicted nanoindentation hardness on the basal plane is 1.02 ± 0.09 GPa. Nanoindentation on the (100) and (010) (nonbasal) planes yields a non-Hertzian response; this is attributed to an effective “softening” due to elastic bending of the Molecular layers. Si...
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anisotropy in surface initiated melting of the triclinic Molecular Crystal 1 3 5 triamino 2 4 6 trinitrobenzene a Molecular dynamics study
Journal of Chemical Physics, 2015Co-Authors: Nithin Mathew, Thomas D Sewell, Donald L ThompsonAbstract:Surface-initiated melting of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a triclinic Molecular Crystal, was investigated using Molecular dynamics simulations. Simulations were performed for the three principal Crystallographic planes exposed to vacuum, with the normal vectors to the planes given by b × c, c × a, and a × b (where a, b, and c define the edge vectors of the unit cell), denoted as (100), (010), and (001), respectively. The best estimate of the normal melting temperature for TATB is 851 ± 5 K. The nature and extent of disordering of the Crystal-vacuum interface depend on the exposed Crystallographic face, with the (001) face exhibiting incomplete melting and superheating. This is attributed to the anisotropy of the inter-Molecular hydrogen bonding and the propensity of the Crystal to form stacking faults in directions approximately perpendicular to the (100) and (010) faces. For all three Crystal orientations, formation of Molecular vacancies in the lattice at the Crystal-vacuum (or Crystal-quasi-liquid layer) interface precedes the complete loss of order at the interface.
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first principles based calculations of vibrational normal modes in polyatomic materials with translational symmetry application to petn Molecular Crystal
Journal of Physical Chemistry B, 2008Co-Authors: Kirill A Velizhanin, Svetlana Kilina, Thomas D Sewell, Andrei PiryatinskiAbstract:Numerical studies of vibrational energy transport and associated (non)linear infrared and Raman response in polyatomic materials require knowledge of the multidimensional vibrational potential-energy surface and the ability to perform normal-mode analysis on that potential. The presence of translational symmetry, as in Crystals, leads to the observed dispersion of the unit cell normal modes and has to be accounted for in calculations of energy transfer rates and other spectroscopic quantities. Here we report on the implementation of a computational approach that combines the generalized supercell method and density functional theory electronic structure calculations to investigate the vibrational structure in translationally symmetric materials containing relatively large numbers of atoms in the unit cell (58 atoms in the present study). The method is applied to calculate the phonon and vibron dispersion relations and the vibrational density of states in pentaerythritol tetranitrate (PETN) Molecular Crystal which is an important energetic material. The results set the stage for future investigations of vibrational energy transport and associated nonlinear spectroscopic signatures in this class of materials.
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shock induced shear bands in an energetic Molecular Crystal application of shock front absorbing boundary conditions to Molecular dynamics simulations
Physical Review B, 2008Co-Authors: Marc J Cawkwell, Thomas D Sewell, Lianqing Zheng, Donald L ThompsonAbstract:The response of the energetic Molecular Crystal cyclotrimethylene trinitramine (RDX) to the propagation of planar shock waves normal to (100) has been studied using large-scale Molecular dynamics simulations that employ an accurate and transferable nonreactive potential. The propagation of the shock waves was simulated using nonequilibrium Molecular dynamics. Shear bands were nucleated during shocks with a particle velocity of $1.0\text{ }\text{km}\text{ }{\text{s}}^{\ensuremath{-}1}$ and corresponding Rankine-Hugoniot shock pressure of 9.7 GPa. These defects propagate into the compressed material at $45\ifmmode^\circ\else\textdegree\fi{}$ to [100] in the [010] zone. The shear bands evolve slowly compared to the time scales routinely accessible to nonequilibrium Molecular dynamics toward a liquidlike state as a result of viscous heating. A recently developed shock-front absorbing boundary condition [A. V. Bolesta et al., Phys. Rev. B 76, 224108 (2007)] was applied to the simulation cells at the moment of maximum compression to sustain the shock-compressed state. Molecular dynamics simulations were then employed to study the temporal and structural evolution of the shock-induced shear bands toward a steady-fluctuating state. Owing to the intense, viscous flow-driven heating within the shear bands, these defects can be considered to be homogeneously nucleated hot spots.
Nithin Mathew - One of the best experts on this subject based on the ideXlab platform.
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nanoindentation of the triclinic Molecular Crystal 1 3 5 triamino 2 4 6 trinitrobenzene a Molecular dynamics study
Journal of Physical Chemistry C, 2016Co-Authors: Nithin Mathew, Thomas D SewellAbstract:Nanoindentation of the insensitive energetic Molecular Crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) was studied using constant-temperature and constant-energy Molecular dynamics simulations. Displacement-controlled indentations at constant velocity were performed using a rigid, spherical indenter on the three principal Crystallographic planes, (100), (010), and (001). The force–displacement curve for the (001) (basal) plane exhibits a distinct elastic region in agreement with the analytical solution for indentation of an anisotropic half-space by a parabola of revolution. Stiffening precedes inelastic deformation, and the elastic–inelastic transition occurs with kinking and delamination of the layered basal planes and significant pile-up. The predicted nanoindentation hardness on the basal plane is 1.02 ± 0.09 GPa. Nanoindentation on the (100) and (010) (nonbasal) planes yields a non-Hertzian response; this is attributed to an effective “softening” due to elastic bending of the Molecular layers. Si...
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anisotropy in surface initiated melting of the triclinic Molecular Crystal 1 3 5 triamino 2 4 6 trinitrobenzene a Molecular dynamics study
Journal of Chemical Physics, 2015Co-Authors: Nithin Mathew, Thomas D Sewell, Donald L ThompsonAbstract:Surface-initiated melting of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a triclinic Molecular Crystal, was investigated using Molecular dynamics simulations. Simulations were performed for the three principal Crystallographic planes exposed to vacuum, with the normal vectors to the planes given by b × c, c × a, and a × b (where a, b, and c define the edge vectors of the unit cell), denoted as (100), (010), and (001), respectively. The best estimate of the normal melting temperature for TATB is 851 ± 5 K. The nature and extent of disordering of the Crystal-vacuum interface depend on the exposed Crystallographic face, with the (001) face exhibiting incomplete melting and superheating. This is attributed to the anisotropy of the inter-Molecular hydrogen bonding and the propensity of the Crystal to form stacking faults in directions approximately perpendicular to the (100) and (010) faces. For all three Crystal orientations, formation of Molecular vacancies in the lattice at the Crystal-vacuum (or Crystal-quasi-liquid layer) interface precedes the complete loss of order at the interface.
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Peierls stress of dislocations in Molecular Crystal cyclotrimethylene trinitramine.
Journal of Physical Chemistry A, 2013Co-Authors: Nithin Mathew, Catalin R. Picu, Peter W. ChungAbstract:Dislocation mediated plasticity in the α phase of the energetic Molecular Crystal cyclotrimethylene trinitramine (RDX) was investigated using a combination of atomistic simulations and the Peierls-Nabarro (PN) model. A detailed investigation of core structures and dislocation Peierls stress was conducted using athermal atomistic simulations at atmospheric pressure to determine the active slip systems. Generalized stacking fault energy surfaces calculated using atomistic simulations were used in the PN model to also estimate the critical shear stress for dislocation motion. The primary slip plane is found to be (010) in agreement with experimental observations, with the (010)[100] slip systems having the lowest Peierls stress. In addition, atomistic simulations predict the (021)[01[overline]2], (021)[100], (011)[100], (001)[100], and (001)[010] slip systems to have Peierls stress values small enough to allow plastic activity. However, there are less than five independent slip systems in this material in all situations. The ranking of slip systems based on the Peierls stress values is provided, and implications are discussed in relation to experimental data from nanoindentation and shock-induced plastic deformation.
Hengbo Cui - One of the best experts on this subject based on the ideXlab platform.
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high pressure Crystal structure and electrical properties of a single component Molecular Crystal ni dddt 2 dddt 5 6 dihydro 1 4 dithiin 2 3 dithiolate
Molecules, 2019Co-Authors: Hengbo Cui, Takao Tsumuraya, Hamish H.-m. Yeung, Chloe S. Coates, Mark R. Warren, Reizo KatoAbstract:Single-component Molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and Crystal structure of the single-component Crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component Molecular Crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single Crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and interMolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined Crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures.
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High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)
MDPI AG, 2019Co-Authors: Hengbo Cui, Takao Tsumuraya, Hamish H.-m. Yeung, Chloe S. Coates, Mark R. Warren, Reizo KatoAbstract:Single-component Molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and Crystal structure of the single-component Crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component Molecular Crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single Crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and interMolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined Crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures
Yoshinori Tokura - One of the best experts on this subject based on the ideXlab platform.
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electronic ferroelectricity in a Molecular Crystal with large polarization directing antiparallel to ionic displacement
Physical Review Letters, 2012Co-Authors: Kensuke Kobayashi, Sachio Horiuchi, Reiji Kumai, Yoshinori Tokura, Fumitaka Kagawa, Youichi MurakamiAbstract:Ferroelectric polarization of 6.3 μC cm(-2) is induced by the neutral-to-ionic transition, upon which nonpolar molecules of electron donor tetrathiafulvalene (TTF) and acceptor p-chloranil (CA) are incompletely ionized to ±0.60e and dimerized along the Molecular stacking chain. We find that the ferroelectric properties are governed by interMolecular charge transfer rather than simple displacement of static point charge on molecules. The observed polarization and poling effect on the absolute structural configuration can be interpreted in terms of electronic ferroelectricity, which not only exhibits antiparallel polarity to the ionic displacement but also enhances the polarization more than 20 times that of the point-charge model.
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electronic ferroelectricity in a Molecular Crystal with large polarization directing antiparallel to ionic displacement
Physical Review Letters, 2012Co-Authors: Kensuke Kobayashi, Sachio Horiuchi, Reiji Kumai, Yoshinori Tokura, Fumitaka Kagawa, Youichi MurakamiAbstract:nonpolar molecules of electron donor tetrathiafulvalene (TTF) and acceptor p-chloranil (CA) are incompletely ionized to � 0:60e and dimerized along the Molecular stacking chain. We find that the ferroelectric properties are governed by interMolecular charge transfer rather than simple displacement of static point charge on molecules. The observed polarization and poling effect on the absolute structural configuration can be interpreted in terms of electronic ferroelectricity, which not only exhibits antiparallel polarity to the ionic displacement but also enhances the polarization more than 20 times that of the pointcharge model.
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above room temperature ferroelectricity in a single component Molecular Crystal
Nature, 2010Co-Authors: Sachio Horiuchi, Yusuke Tokunaga, Gianluca Giovannetti, Silvia Picozzi, Hirotake Itoh, Ryo Shimano, Reiji Kumai, Yoshinori TokuraAbstract:Ferroelectric compounds have a range of properties useful in practical applications, including polarity reversal in electric fields, temperature sensitivity and the ability to convert mechanical stress into electricity. It is generally assumed that ferroelectricity is rare and mostly poor in organic compounds, but Horiuchi et al. now report the discovery of above-room-temperature ferroelectricity with relatively high polarization in the organic Crystal croconic acid, a component of black dyes. These properties are not readily apparent in the Crystalline form of this simple molecule, but they emerge on application of a modest electric field that induces a Molecular-topological keto-enol conversion. This finding raises the prospect that organic ferroelectrics might be much more abundant that previously thought. Ferroelectrics are electro-active materials that can store and switch their polarity, sense temperature changes, interchange electric and mechanical functions, and manipulate light. Subtle changes in the topology of certain chemical bonds have long been identified as a possible route for achieving ferroelectricity in organic Molecular Crystals. Ferroelectricity above room temperature is now demonstrated by applying an electric field to coherently align the Molecular polarities in Crystalline croconic acid. Ferroelectrics are electro-active materials that can store and switch their polarity (ferroelectricity), sense temperature changes (pyroelectricity), interchange electric and mechanical functions (piezoelectricity), and manipulate light (through optical nonlinearities and the electro-optic effect): all of these functions have practical applications. Topological switching of π-conjugation in organic molecules, such as the keto-enol transformation, has long been anticipated as a means of realizing these phenomena in Molecular assemblies and Crystals1. Croconic acid, an ingredient of black dyes2, was recently found to have a hydrogen-bonded polar structure in a Crystalline state3. Here we demonstrate that application of an electric field can coherently align the Molecular polarities in Crystalline croconic acid, as indicated by an increase of optical second harmonic generation, and produce a well-defined polarization hysteresis at room temperature. To make this simple pentagonal molecule ferroelectric, we switched the π-bond topology using synchronized proton transfer instead of rigid-body rotation. Of the organic ferroelectrics, this Molecular Crystal exhibits the highest spontaneous polarization (∼20 μC cm-2) in spite of its small Molecular size, which is in accord with first-principles electronic-structure calculations. Such high polarization, which persists up to 400 K, may find application in active capacitor and nonlinear optics elements in future organic electronics.
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above room temperature ferroelectricity in a single component Molecular Crystal
Nature, 2010Co-Authors: Sachio Horiuchi, Yusuke Tokunaga, Gianluca Giovannetti, Silvia Picozzi, Hirotake Itoh, Ryo Shimano, Reiji Kumai, Yoshinori TokuraAbstract:Ferroelectrics are electro-active materials that can store and switch their polarity (ferroelectricity), sense temperature changes (pyroelectricity), interchange electric and mechanical functions (piezoelectricity), and manipulate light (through optical nonlinearities and the electro-optic effect): all of these functions have practical applications. Topological switching of pi-conjugation in organic molecules, such as the keto-enol transformation, has long been anticipated as a means of realizing these phenomena in Molecular assemblies and Crystals. Croconic acid, an ingredient of black dyes, was recently found to have a hydrogen-bonded polar structure in a Crystalline state. Here we demonstrate that application of an electric field can coherently align the Molecular polarities in Crystalline croconic acid, as indicated by an increase of optical second harmonic generation, and produce a well-defined polarization hysteresis at room temperature. To make this simple pentagonal molecule ferroelectric, we switched the pi-bond topology using synchronized proton transfer instead of rigid-body rotation. Of the organic ferroelectrics, this Molecular Crystal exhibits the highest spontaneous polarization ( approximately 20 muC cm(-2)) in spite of its small Molecular size, which is in accord with first-principles electronic-structure calculations. Such high polarization, which persists up to 400 K, may find application in active capacitor and nonlinear optics elements in future organic electronics.