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S. Veprek – One of the best experts on this subject based on the ideXlab platform.

  • phase stAbilities and thermal decomposition in the zr1 xalxn system studied by Ab Initio calculation and thermodynamic modeling
    Acta Materialia, 2008
    Co-Authors: S. H. Sheng, R. F. Zhang, S. Veprek
    Abstract:

    Abstract The Ab Initio density funcfunctional 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 freefree 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.

  • 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, 2008
    Co-Authors: R. F. Zhang, S. Veprek
    Abstract:

    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 freefree 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 vapovaporosition experiments. The constructed Gibbs freefree 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.

  • Phase stAbilities and thermal decomposition in the Zr1-xAlxN system studied by Ab Initio calculation and thermodynamic modeling
    Acta Materialia, 2008
    Co-Authors: S. H. Sheng, R. F. Zhang, S. Veprek
    Abstract:

    The Ab Initio density funcfunctional 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 freefree 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.

  • Electron transport through Al-ZnO-Al: an Ab Initio calculation
    ArXiv eprints, 2010
    Co-Authors: Z. J. Yang, Zijiang Yang, L H Wan, Langhui Wan, Yunjin Yu, Yadong Wei, Jian Wang
    Abstract:

    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 funcfunctional 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 capacapacitance which exhibits three plateaus at different bias voltages which may have potential device application.

  • Electron transport through Al–ZnO–Al: an Ab Initio calculation
    Journal of Applied Physics, 2010
    Co-Authors: Z. J. Yang, L H Wan, Yunjin Yu, Yadong Wei, Jian Wang
    Abstract:

    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 funcfunctional 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 capacapacitance 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.

Paul Rulis – One of the best experts on this subject based on the ideXlab platform.

  • Intrinsic Mechanical Properties of 20 MAX‐Phase Compounds
    Journal of the American Ceramic Society, 2013
    Co-Authors: Wai Yim Ching, Yuxiang Mo, Sitaram Aryal, Paul Rulis
    Abstract:

    The intrinsic mechanical properties of 20 MAX-phase compounds are calculated using an Ab Initio Method based on density funcfunctional 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 hardhardness in MAX compounds has no apparent correlation with any of the calculated mechanical parameters or their combinations.

  • Intrinsic mechanical properties of 20 MAX-phase compounds
    Journal of the American Ceramic Society, 2013
    Co-Authors: Wai Yim Ching, Yuxiang Mo, Sitaram Aryal, Paul Rulis
    Abstract:

    The intrinsic mechanical properties of 20 MAX-phase compounds are calculated using an Ab Initio Method based on density funcfunctional 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 hardhardness 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.

  • phase stAbilities and thermal decomposition in the zr1 xalxn system studied by Ab Initio calculation and thermodynamic modeling
    Acta Materialia, 2008
    Co-Authors: S. H. Sheng, R. F. Zhang, S. Veprek
    Abstract:

    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.

  • Phase stAbilities and thermal decomposition in the Zr1-xAlxN system studied by Ab Initio calculation and thermodynamic modeling
    Acta Materialia, 2008
    Co-Authors: S. H. Sheng, R. F. Zhang, S. Veprek
    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 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.