| 1. |
- Hu, Qing-Miao, et al.
(författare)
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Site occupancy, magnetic moments, and elastic constants of off-stoichiometric Ni2MnGa from first-principles calculations
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:14
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Tidskriftsartikel (refereegranskat)abstract
- The site occupancy and elastic modulus of off-stoichiometric Ni2MnGa alloys are investigated by the use of the first-principles exact muffin-tin orbital method in combination with coherent-potential approximation. The stable site occupancy at 300 K is determined by comparing the free energies of the alloys with different site-occupation configurations. It is shown that, for most of the off-stoichiometric Ni2MnGa, the "normal" site occupation is favorable, i.e., the excess atoms of the rich component occupy the sublattice(s) of the deficient one(s). Nevertheless, for the Ga-rich alloys, the excess Ga atoms have strong tendency to take the Mn sublattice no matter if Mn is deficient or not. Based on the determined site occupancy, the elastic moduli of the off-stoichiometric Ni2MnGa are calculated. We find that, in general, the bulk modulus increases with increasing e/a ratio (i.e., the number of valence electrons per atom). The shear moduli C-' and C-44 change oppositely with e/a ratio: C-' decreases but C-44 increases with increasing e/a. However, the Mn-rich Ga-deficient alloys deviate significantly from this general trend. The correlation of calculated elastic moduli and available experimental martensitic transformation temperatures (T-M) demonstrates that the alloy with larger C-' than that of the perfect Ni2MnGa generally possesses lower T-M except for Ni2Mn1+xGa1-x.
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| 2. |
- Lu, S., et al.
(författare)
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Rare earth elements in alpha-Ti : A first-principles investigation
- 2009
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Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 46:4, s. 1187-1191
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Tidskriftsartikel (refereegranskat)abstract
- The interaction energies between substitutional rare earth (RE) atoms, between RE and interstitial C, N, O, H atoms, as well as between RE and vacancies in alpha-Ti are calculated via first-principles density-functional theory with projector augmented-wave (PAW) pseudopotentials. The results show that the RE-vacancy and RE-RE interactions are attractive due to the weaker RE-Ti bond than the host Ti-Ti bond. All of the RE atoms investigated in this paper are repulsive to C and N, but attractive to H. RE-O interactions are repulsive for the light RE atoms, though the interactions are very weak for the heavy RE atoms. The mechanism underlying the interactions and their possible influence on the properties of Ti alloys are discussed.
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