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Free Energy Simulation Of Grain Boundary Segregation And Thermodynamics In Ni3−Xal1+X, R. Najafabadi, H.Y. Wang, D. J. Srolovitz, Richard Alan Lesar
Free Energy Simulation Of Grain Boundary Segregation And Thermodynamics In Ni3−Xal1+X, R. Najafabadi, H.Y. Wang, D. J. Srolovitz, Richard Alan Lesar
Richard Alan Lesar
The free energy simulation method is employed to study segregation to Σ5 and Σ13 (001) twist grain boundaries and their free energies in ordered Ni3−xAl1+x. In the temperature range studied (300–900K), it is shown that there is almost no segregation, strong Al segregation, and weak Ni segregation to the grain boundary for the stoichiometric, Al-rich, and Ni-rich bulk compositions respectively. It is also shown that the segregation is limited to a few (002) planes around the grain boundary and its magnitude decreases with increasing temperature. For Al-rich bulk composition, it is demonstrated that segregation at low temperature substantially lowers the …
Theory Of Compositional And Magnetic Correlations In Alloys: Interpretation Of A Diffuse Neutron-Scattering Experiment On An Iron-Vanadium Single Crystal, J. B. Staunton, Duane D. Johnson, F. J. Pinski
Theory Of Compositional And Magnetic Correlations In Alloys: Interpretation Of A Diffuse Neutron-Scattering Experiment On An Iron-Vanadium Single Crystal, J. B. Staunton, Duane D. Johnson, F. J. Pinski
Duane D. Johnson
We describe a first-principles theory for compositional and magnetic correlations in alloys and compare the results of the theory with recent diffuse, unpolarized, neutron-scattering measurements on a single crystal of ferromagnetic Fe0.865V0.135. The nuclear cross section is described very well by the theory and we are able to connect the q-dependent structure to the underlying electronic structure of the alloy. The magnetocompositional and magnetic correlations also may be obtained for comparison to polarized measurements.
Total-Energy And Pressure Calculations For Random Substitutional Alloys, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Györffy, G. M. Stocks
Total-Energy And Pressure Calculations For Random Substitutional Alloys, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Györffy, G. M. Stocks
Duane D. Johnson
We present the details and the derivation of density-functional-based expressions for the total energy and pressure for random substitutional alloys (RSA) using the Korringa-Kohn-Rostoker Green’s-function approach in combination with the coherent-potential approximation (CPA) to treat the configurational averaging. This includes algebraic cancellation of various electronic core contributions to the total energy and pressure, as in ordered-solid muffin-tin-potential calculations. Thus, within the CPA, total-energy and pressure calculations for RSA have the same foundation and have been found to have the same accuracy as those obtained in similar calculations for ordered solids. Results of our calculations for the impurity formation energy, and …
Finite Temperature Structure And Thermodynamics Of The Au Σ5 (001) Twist Boundary, R. Najafabadi, D. J. Srolovitz, Richard Alan Lesar
Finite Temperature Structure And Thermodynamics Of The Au Σ5 (001) Twist Boundary, R. Najafabadi, D. J. Srolovitz, Richard Alan Lesar
Richard Alan Lesar
The structure and thermodynamic properties of a Σ5 (001) twist boundary in gold are studied as a function of temperature. This study was performed within the framework of the Local Harmonic (LH) model and employed an Embedded Atom Method (EAM) potential for gold. We find that for the Σ5 (001) twist boundary in gold, a distorted CSL structure is stable at low temperatures, but undergoes a phase transformation to a DSC related structure near room temperature. This transformation is shown to be first order. The temperature dependences of the excess grain boundary free energy, enthalpy, entropy, specific heat, and excess …
Coincidence Orientations Of Crystals In Tetragonal Systems, With Applications To Yba2cu3o7, Abha Singh, N. Chandrasekhar, Alexander H. King
Coincidence Orientations Of Crystals In Tetragonal Systems, With Applications To Yba2cu3o7, Abha Singh, N. Chandrasekhar, Alexander H. King
Alexander H. King
We have developed a method for the characterization of coincidence-site lattices (CSL's) in tetragonal or near-tetragonal orthorhombic structures, by suitable modifications to the method of Grimmer & Warrington [Acta Cryst. (1987), A43, 232-243]. We have applied our method to determine coincidence rotations and the associated information appropriate for forming constrained CSL's in the high-To superconductor YBazCu307-n. The unit cell is orthorhombic with lattice parameters a = 3.82, b = 3"89 and c = 11.67 A for the nominal composition. We present tables of coincidence rotation angles, .Z, CSL, DSCL and associated step vectors up to ,~ = 50. We find …
Calculated Thermodynamic Properties And Phase Transitions Of Solid N2 At Temperatures 0≤T≤300 K And Pressures 0≤P≤100 Gpa, J. Belak, Richard Alan Lesar, R. D. Etters
Calculated Thermodynamic Properties And Phase Transitions Of Solid N2 At Temperatures 0≤T≤300 K And Pressures 0≤P≤100 Gpa, J. Belak, Richard Alan Lesar, R. D. Etters
Richard Alan Lesar
Thermodynamic properties of solid nitrogen are calculated over a variety of isotherms and isobars using a constant pressure Monte Carlo method with deformable, periodic boundary conditions. Vibron frequencies are calculated using a simple perturbation theory. In addition, pressure–volume relations, thermal expansion coefficients, structures, and phase transition pressures and temperatures are determined. In particular, the nature of the orientational disorder in the plastic crystal phases is examined by calculating a variety of orientational order parameters.
Location Of Melting Point At 300 K Of Nitrogen By Monte Carlo Simulation, Evert Jan Meijer, Daan Frenkel, Richard Alan Lesar, Anthony J.C. Ladd
Location Of Melting Point At 300 K Of Nitrogen By Monte Carlo Simulation, Evert Jan Meijer, Daan Frenkel, Richard Alan Lesar, Anthony J.C. Ladd
Richard Alan Lesar
We present an accurate new method to compute absolute free energies of molecular solids by computer simulations. As a first application, we computed the thermodynamicphase transition between the fluid phase and the orientational disordered solid β phase of nitrogen at 300 K, using a well tested pair potential. The computed coexistence pressure and the volume change coincides within the error margins with the experimental values. The coexistence volume differed by 2% from the experimental value. To our knowledge these results constitutes the first numerical calculation of the thermodynamic stability for a model of a realistic molecular solid.