ABSTRACT
The article contains computational data of many-body interactions in Al-Cu alloys, obtained using PAW-VASP calculations. Pairwise, three-site, and four-site interactions are presented. Mentioned data are relevant to the research article "Many-body mechanism of Guinier-Preston zones stabilization in Al-Cu alloys" (Gorbatov et al., 2017) [1].
ABSTRACT
The elastic properties of pure iron and substitutionally disordered 10 at. % Cr Fe-Cr alloy are investigated as a function of temperature by using first-principles electronic-structure calculations by the exact muffin-tin orbitals method. The temperature effects on the elastic properties are included via the electronic, magnetic, and lattice expansion contributions. We show that the degree of magnetic order in both pure iron and Fe(90)Cr(10) alloy mainly determines the dramatic change of the elastic anisotropy of these materials at elevated temperatures. The effect of lattice expansion is found to be secondary but also very important for quantitative modeling.
ABSTRACT
Migration barriers for diffusion of interstitial Mn in the dilute magnetic semiconductor (Ga,Mn)As are studied using first-principles calculations. The diffusion pathway goes through two types of interstitial sites: As coordinated and Ga coordinated. The energy profile along the path is found to depend on the ratio of concentrations between substitutional and interstitial Mn in GaAs. Two regions of distinctly different behavior, corresponding to n-type and p-type (Ga,Mn)As, are identified. The difference in mobility is a reflection of the change in the charge state of Mn interstitials (double donors) that occurs in the presence of substitutional Mn impurities (acceptors). In addition, substitutional Mn impurities are shown to act as traps for interstitial Mn. The effective migration barrier for the positively doubly charged Mn interstitials in p-type (Ga,Mn)As is estimated to vary from 0.55 to about 0.95 eV.
ABSTRACT
The surprisingly low magnetic transition temperatures in austenitic stainless steels indicate that in these Fe-based alloys magnetic disorder might be present at room temperature. Using a first-principles approach, we have obtained a theoretical description of the stacking fault energy in Fe(100-c-n)Cr(c)Ni(n) alloys as a function of composition and temperature. Comparison of our results with experimental databases provides a strong evidence for large magnetic fluctuations in these materials. We demonstrate that the effects of alloying additions on the structural properties of steels contain a dominant magnetic contribution, which stabilizes the most common austenitic steels at normal service conditions.
ABSTRACT
We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga(1)-(x)Mn(x))As lower the total energy, compared to the case of perfect ferromagnetic ordering, when As defects on the Ga sublattice are present. Such magnetic structures are found to be stable for a range of concentrations of As antisites, and this result accounts for the observed magnetic moments and critical temperatures in (Ga(1)-(x)Mn(x))As. We propose an explanation for the stabilization of the partially disordered magnetic structures and conclude that the magnetization and critical temperatures should increase substantially by reducing the number of As antisite defects.
ABSTRACT
The most recent advances in theory and methodology are directed towards obtaining a quantitative description of the electronic structure and physical properties of alloy steels. Specifically, we employ ab initio alloy theories to map the elastic properties of austenitic stainless steels as a function of chemical composition. The so generated data can be used in the search for new steel grades, and, as an example, we predict two basic compositions with outstanding properties among the austenitic stainless steels.
ABSTRACT
The phase diagram for the vacancy-ordered structures in the substoichiometric TiC(x) (x = 0.5-1.0) has been established from Monte Carlo simulations with the long-range pair and multisite effective interactions obtained from ab initio calculations. Three ordered superstructures of vacancies (Ti(2)C, Ti(3)C(2), and Ti(6)C(5)) are found to be ground state configurations. Their stability has been verified by full-potential total energy calculations of the fully relaxed structures.
