The Experts below are selected from a list of 21084 Experts worldwide ranked by ideXlab platform
S. Veprek - One of the best experts on this subject based on the ideXlab platform.
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phase stAbilities and thermal decomposition in the zr1 xalxn system studied by Ab Initio calculation and thermodynamic modeling
Acta Materialia, 2008Co-Authors: S. H. Sheng, R. F. Zhang, S. VeprekAbstract:Abstract The Ab Initio density functional theory is used to calculate the lattice constants, total energy and bulk modulus of binary hexagonal close packed (hcp) and face-centered cubic (fcc) ZrN, AlN and ternary Zr 1− x Al x N phases. The calculated results are supported by previously reported experimental and theoretical data. The lattice stAbilities of binary phases and demixing energies of ternary phases calculated by the Ab Initio Method are then used in thermodynamic modeling to construct the Gibbs free energy diagram of the immiscible quasi-binary ZrN–AlN system at different temperatures. The results show that, for the composition x ⩽ 0.472, Zr 1− x Al x N solid solutions are more stAble in fcc than in hcp structure, which is in a good agreement with the experimentally reported value of x 1− x Al x N solution coatings should undergo phase decomposition into fcc ZrN and fcc AlN. However, considering the relatively large lattice mismatch between the fcc ZrN and the fcc AlN, the coherent spinodal decomposition may probAbly be hindered due to rapid phase transformation from fcc AlN to the stAble hcp AlN. This is supported experimentally in that no intermediate fcc AlN has so far been observed in the Zr–Al–N system.
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phase stAbilities of self organized nc tin a si3n4 nanocomposites and of ti1 xsixny solid solutions studied by Ab Initio calculation and thermodynamic modeling
Thin Solid Films, 2008Co-Authors: R. F. Zhang, S. VeprekAbstract:Abstract Bulk properties of stAble binary fcc-TiN and hcp(β)-Si 3 N 4 , hypothetical fcc-SiN and hcp(β)-Ti 3 N 4 , and ternary Ti 1 − x Si x N y phases are calculated by Ab Initio Method. The values of total energies are then used for thermodynamic calculations of the lattice instAbilities of hypothetical binary phases of fcc-SiN and hcp-Ti 3 N 4 , and of the interaction parameters of ternary Ti 1 − x Si x N y phases. Based on these data, Gibbs free energy diagrams of the quasi-binary TiN y –SiN y system are constructed in order to study the relative phase stAbility of the metastAble ternary fcc- and hcp-Ti 1 − x Si x N y phases over the entire range of compositions. The results are supported by the published data from chemical and physical vapor deposition experiments. The constructed Gibbs free energy diagram and phase selection diagram of quasi-binary TiN y –SiN y system in fcc structure show that metastAble fcc-Ti 1 − x Si x N coatings should undergo chemically spinodal decomposition into coherent fcc-TiN and fcc-SiN. Due to a high lattice mismatch between fcc-TiN and hcp-Si 3 N 4 , and to much higher lattice instAbility of fcc-SiN with respect to stAble hcp-Si 3 N 4 , only About one monolayer of pseudomorphic SiN y interfacial phase is stAble.
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Phase stAbilities and thermal decomposition in the Zr1-xAlxN system studied by Ab Initio calculation and thermodynamic modeling
Acta Materialia, 2008Co-Authors: S. H. Sheng, R. F. Zhang, S. VeprekAbstract:The Ab Initio density functional theory is used to calculate the lattice constants, total energy and bulk modulus of binary hexagonal close packed (hcp) and face-centered cubic (fcc) ZrN, AlN and ternary Zr1-xAlxN phases. The calculated results are supported by previously reported experimental and theoretical data. The lattice stAbilities of binary phases and demixing energies of ternary phases calculated by the Ab Initio Method are then used in thermodynamic modeling to construct the Gibbs free energy diagram of the immiscible quasi-binary ZrN-AlN system at different temperatures. The results show that, for the composition x ≤ 0.472, Zr1-xAlxN solid solutions are more stAble in fcc than in hcp structure, which is in a good agreement with the experimentally reported value of x < 0.43. The constructed chemically binodal and spinodal decomposition curves show that fcc Zr1-xAlxN solution coatings should undergo phase decomposition into fcc ZrN and fcc AlN. However, considering the relatively large lattice mismatch between the fcc ZrN and the fcc AlN, the coherent spinodal decomposition may probAbly be hindered due to rapid phase transformation from fcc AlN to the stAble hcp AlN. This is supported experimentally in that no intermediate fcc AlN has so far been observed in the Zr-Al-N system. © 2007 Acta Materialia Inc.
Jian Wang - One of the best experts on this subject based on the ideXlab platform.
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Electron transport through Al-ZnO-Al: an Ab Initio calculation
ArXiv eprints, 2010Co-Authors: Z. J. Yang, Yunjin Yu, Yadong Wei, L H Wan, Langhui Wan, Zijiang Yang, Jian WangAbstract:The electron transport properties of ZnO nano-wires coupled by two aluminium electrodes were studied by it Ab Initio Method based on non-equilibrium Green's function approach and density functional theory. A clearly rectifying current-voltage characteristics was observed. It was found that the contact interfaces between Al-O and Al-Zn play important roles in the charge transport at low bias voltage and give very asymmetric I-V characteristics. When the bias voltage increases, the negative differential resistance occurs at negative bias voltage. The charge accumulation was calculated and its behavior was found to be well correlated with the I-V characteristics. We have also calculated the electrochemical capacitance which exhibits three plateaus at different bias voltages which may have potential device application.
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Electron transport through Al–ZnO–Al: an Ab Initio calculation
Journal of Applied Physics, 2010Co-Authors: Z. J. Yang, Yunjin Yu, Yadong Wei, L H Wan, Jian WangAbstract:The electron transport properties of ZnO nanowires coupled by two aluminum electrodes were studied by Ab Initio Method based on nonequilibrium Green’s function approach and density functional theory. A clearly rectifying current-voltage characteristics was observed. It was found that the contact interfaces between Al–O and Al–Zn play important roles in the charge transport at low bias voltage and give very asymmetric I-V characteristics. When the bias voltage increases, the negative differential resistance occurs at negative bias voltage. The charge accumulation was calculated and its behavior was found to be well correlated with the I-V characteristics. We have also calculated the electrochemical capacitance which exhibits three plateaus at different bias voltages which may have potential device application.
Jin-Zong You - One of the best experts on this subject based on the ideXlab platform.
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Study on the thermal decomposition of capecitAbine
Journal of Thermal Analysis and Calorimetry, 2015Co-Authors: Xue-Jie Wang, Jin-Zong YouAbstract:The thermal decomposition of capecitAbine (CAP) was measured with thermogravimetry, differential scanning calorimetry, and thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. The IR spectra, high-performance liquid chromatography, and liquid chromatography–mass spectrometry of CAP and the residue of its thermal decomposition at various temperatures were determined. The molecular bond orders were calculated using an Ab Initio Method from the GAMESS program of quantum chemistry. The mode of thermal decomposition for CAP was discussed. The kinetic parameters for thermal decomposition such as activation energy Ea and the pre-exponential factor A were obtained using the Ozawa Method. The prospective lifetime of CAP was estimated using the Dakin equation. The results indicated that the thermal decomposition of CAP is a three-step process, and the first mass loss stage is to lose pentyl formate. The initial decomposition temperature in either nitrogen or air is 120 °C. For decomposition in nitrogen, the Ea and A for the initial thermal decomposition are 105.1 kJ mol−1 and 9.12 × 1011 min−1, respectively. For decomposition in air, the corresponding Ea and A are 105.1 kJ mol−1 and 9.55 × 1011 min−1, respectively. The CAP has poor thermal stAbility under routine temperature.
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Study on the molecular structure and thermal stAbility of pyrimidine nucleoside analogs
Journal of Thermal Analysis and Calorimetry, 2015Co-Authors: Xue-Jie Wang, Jin-Zong YouAbstract:The thermal decomposition processes for ten pyrimidine nucleoside analogs were measured with thermogravimetry and differential scanning calorimetry. The IR spectra, high-performance liquid chromatography, and liquid chromatography–mass spectrometry of pyrimidine nucleoside analogs and their residues of thermal decomposition at various temperatures were determined. The molecular bond orders of pyrimidines and pyrimidine nucleoside analogs were calculated with an Ab Initio Method from the GAMESS program. We then discuss mechanisms of thermal decomposition in these pyrimidine nucleoside analogs. The results indicate that there are four types of mechanisms. The decomposition mechanism depends on the relative strength of the peptide bond and the amide bond within pyrimidine ring and whether or not accompanied by oxidation reaction. The substituent groups affect the thermal stAbility and the thermal decomposition mechanism of pyrimidine nucleoside analogs. Increasing the number of electron-donating groups on the pyrimidine ring and furan ring will enhance the peptide bond, and will elevate the temperature of thermal decomposition. There is a positive correlation between the molecular bond orders calculated by quantum chemistry and the thermal decomposition temperature of pyrimidine nucleoside analogs. The stronger the weakest bond order, the higher the decomposition temperature. The molecular bond orders thus can be used as a basis to judge molecular thermal stAbility for analog compounds with similar molecular structure, size, and energy.
Paul Rulis - One of the best experts on this subject based on the ideXlab platform.
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Intrinsic Mechanical Properties of 20 MAX‐Phase Compounds
Journal of the American Ceramic Society, 2013Co-Authors: Wai Yim Ching, Sitaram Aryal, Yuxiang Mo, Paul RulisAbstract:The intrinsic mechanical properties of 20 MAX-phase compounds are calculated using an Ab Initio Method based on density functional theory. A stress versus strain approach is used to obtain the elastic coefficients and thereby obtain the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio based on the Voigt–Reuss–Hill (VRH) approximation for polycrystals. The results are in good agreement with availAble experimental data. It is shown that there is an inverse correlation between Poisson's ratio and the Pugh ratio of shear modulus to bulk modulus in MAX phases. Our calculations also indicate that two MAX compounds, Ti2AsC and Ti2PC, show much higher ductility than the other compounds. It is concluded that the MAX-phase compounds have a wide range of mechanical properties ranging from very ductile to brittle with the “A” in the MAX phase being the most important controlling element. The measured Vickers hardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations.
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Intrinsic mechanical properties of 20 MAX-phase compounds
Journal of the American Ceramic Society, 2013Co-Authors: Wai Yim Ching, Sitaram Aryal, Yuxiang Mo, Paul RulisAbstract:The intrinsic mechanical properties of 20 MAX-phase compounds are calculated using an Ab Initio Method based on density functional theory. A stress versus strain approach is used to obtain the elastic coefficients and thereby obtain the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio based on the Voigt-Reuss-Hill (VRH) approximation for polycrystals. The results are in good agreement with availAble experimental data. It is shown that there is an inverse correlation between Poisson's ratio and the Pugh ratio of shear modulus to bulk modulus in MAX phases. Our calculations also indicate that two MAX compounds, Ti2AsC and Ti2PC, show much higher ductility than the other compounds. It is concluded that the MAX-phase compounds have a wide range of mechanical properties ranging from very ductile to brittle with the "A" in the MAX phase being the most important controlling element. The measured Vickers hardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations. © 2013 The American Ceramic Society.
S. H. Sheng - One of the best experts on this subject based on the ideXlab platform.
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phase stAbilities and thermal decomposition in the zr1 xalxn system studied by Ab Initio calculation and thermodynamic modeling
Acta Materialia, 2008Co-Authors: S. H. Sheng, R. F. Zhang, S. VeprekAbstract:Abstract The Ab Initio density functional theory is used to calculate the lattice constants, total energy and bulk modulus of binary hexagonal close packed (hcp) and face-centered cubic (fcc) ZrN, AlN and ternary Zr 1− x Al x N phases. The calculated results are supported by previously reported experimental and theoretical data. The lattice stAbilities of binary phases and demixing energies of ternary phases calculated by the Ab Initio Method are then used in thermodynamic modeling to construct the Gibbs free energy diagram of the immiscible quasi-binary ZrN–AlN system at different temperatures. The results show that, for the composition x ⩽ 0.472, Zr 1− x Al x N solid solutions are more stAble in fcc than in hcp structure, which is in a good agreement with the experimentally reported value of x 1− x Al x N solution coatings should undergo phase decomposition into fcc ZrN and fcc AlN. However, considering the relatively large lattice mismatch between the fcc ZrN and the fcc AlN, the coherent spinodal decomposition may probAbly be hindered due to rapid phase transformation from fcc AlN to the stAble hcp AlN. This is supported experimentally in that no intermediate fcc AlN has so far been observed in the Zr–Al–N system.
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Phase stAbilities and thermal decomposition in the Zr1-xAlxN system studied by Ab Initio calculation and thermodynamic modeling
Acta Materialia, 2008Co-Authors: S. H. Sheng, R. F. Zhang, S. VeprekAbstract:The Ab Initio density functional theory is used to calculate the lattice constants, total energy and bulk modulus of binary hexagonal close packed (hcp) and face-centered cubic (fcc) ZrN, AlN and ternary Zr1-xAlxN phases. The calculated results are supported by previously reported experimental and theoretical data. The lattice stAbilities of binary phases and demixing energies of ternary phases calculated by the Ab Initio Method are then used in thermodynamic modeling to construct the Gibbs free energy diagram of the immiscible quasi-binary ZrN-AlN system at different temperatures. The results show that, for the composition x ≤ 0.472, Zr1-xAlxN solid solutions are more stAble in fcc than in hcp structure, which is in a good agreement with the experimentally reported value of x < 0.43. The constructed chemically binodal and spinodal decomposition curves show that fcc Zr1-xAlxN solution coatings should undergo phase decomposition into fcc ZrN and fcc AlN. However, considering the relatively large lattice mismatch between the fcc ZrN and the fcc AlN, the coherent spinodal decomposition may probAbly be hindered due to rapid phase transformation from fcc AlN to the stAble hcp AlN. This is supported experimentally in that no intermediate fcc AlN has so far been observed in the Zr-Al-N system. © 2007 Acta Materialia Inc.
