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First-principles investigations of ordering in binary alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering. (Multiscale Materials Modeling)
2013 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
978-91-7501-880-5 (English)
##### Abstract [en]

The aim of the thesis is to study ordering in binary alloys on the basis of first-principles or {\it ab-initio} techniques employing density functional theory (DFT). The ordering phenomena of materials are of crucial importance for technological applications. The results of the thesis are intended to demonstrate the applicability of the first-principles calculations to provide fundamental insight to the true, namely electronic structure, nature of ordering in binary alloys.

The main part of the thesis focuses on atomic short- and long-range order phenomena in binary alloys as a function of both temperature and chemical composition in FeCo and NiCr alloys. In particular, the influence of magnetism on atomic ordering in FeCo alloys is investigated using the disordered local moment.A large number of concentration dependent effective cluster interactions, derived without the use of any adjustable parameters, are obtained by the SGPM as it is implemented in the EMTO within the CPA. The SGPM interactions can subsequently be used in thermodynamic Monte-Carlo simulations or mean field approximations to determine the ordering phenomena in binary alloys.

First-principles calculations of intrinsic stacking-fault energies (SFE) andanti-phase boundary energies (APBE) in Al$_{3}$Sc and the effects of temperature on SFE and APBE are investigated by using the axial Ising model and supercellapproach. Temperature effects have been taken into consideration byincluding the one-electron thermal excitations in the electronicstructure calculations, and vibrational free energy in the harmonicapproximation as well as by using temperature dependent lattice constants.The latter has been determined within the Debye-Gr{\"u}neisen model,which reproduces well the experimental data.

Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties of B2- FeCo alloy are studied using first-principles calculations. The calculated thermal and elastic properties are found to be in good agreement withthe available measured values when the generalized gradientapproximations is used for the exchange correlation potential.The calculated finite temperature elastic constants show thatthe FeCo alloy is mechanically stable in the ordered phase.Meanwhile, a large elastic anisotropy exhibits a moderate dependence ontemperature.

##### Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , vii, 108 p.
##### Keyword [en]
ordering, random, alloys
##### National Category
Condensed Matter Physics
##### Identifiers
ISBN: 978-91-7501-880-5 (print)OAI: oai:DiVA.org:kth-129313DiVA: diva2:651507
##### Public defence
2013-10-18, B1, Brinellvagen 23, Materials Science and Engineering, KTH, Stockholm, 10:00 (English)
##### Funder
Swedish Research CouncilEU, European Research Council
##### Note

QC 20130927

Available from: 2013-09-27 Created: 2013-09-26 Last updated: 2013-09-27Bibliographically approved
##### List of papers
1. Magnetic state effect upon the order-disorder phase transition in Fe-Co alloys: A first-principles study
Open this publication in new window or tab >>Magnetic state effect upon the order-disorder phase transition in Fe-Co alloys: A first-principles study
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 5, 054202- p.Article in journal (Refereed) Published
##### Abstract [en]

We investigate the effect of global magnetization on the effective cluster interactions and order-disorder phase transition in FexCo1-x alloys. The effective cluster interactions are obtained by the screened generalized perturbation method as it is implemented in the exact muffin-tin orbitals formalism within the coherent potential approximation. The ordering transition from the high-temperature disordered body-centered cubic alloy to the ordered B2 phase is determined by Monte Carlo simulations. The calculated transition temperatures are in good agreement with the available experimental data for the effective interactions, which correspond to the experimentally observed magnetization at the order-disorder phase transition.

##### National Category
Condensed Matter Physics
##### Identifiers
urn:nbn:se:kth:diva-30940 (URN)10.1103/PhysRevB.83.054202 (DOI)000287030300003 ()2-s2.0-79953186924 (Scopus ID)
##### Funder
Swedish Research Council
##### Note
QC 20110318Available from: 2011-03-18 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
2. Temperature dependence of stacking-fault and anti-phase boundary energies in Al3Sc from ab initio calculations
Open this publication in new window or tab >>Temperature dependence of stacking-fault and anti-phase boundary energies in Al3Sc from ab initio calculations
2013 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 93, no 25, 3423-3441 p.Article in journal (Refereed) Published
##### Abstract [en]

Temperature dependence of intrinsic stacking-fault energies (SFE) and anti-phase boundary energies (APBE) of AlSc is investigated in first-principles calculations using the axial Ising model and supercell approach. The temperature effect has been taken into consideration by including the one-electron thermal excitations in the electronic structure calculations, and vibrational free energy in the harmonic approximation as well as by using temperature dependent lattice constant. The latter has been determined within the Debye-Gruneisen model, which reproduces well the experimental data. The APBE and SFE are found to be reduced by about 10% in the temperature interval from 0 to 1000 K. It is shown that the inclusion of the free energy of lattice vibrations in the harmonic approximation increases the SFE further by about 4%. We also find a substantial contribution from local lattice relaxations in the case of APBE for the (111) plane and SFE leading to their reduction by about 30%.

##### Keyword
stacking-fault, anti-phase boundary, (AlSc)-Sc-3, EMTO, SGPM, effective cluster interactions, AIM, LPS
##### National Category
Metallurgy and Metallic Materials
##### Identifiers
urn:nbn:se:kth:diva-129336 (URN)10.1080/14786435.2013.810817 (DOI)000323634500003 ()2-s2.0-84883558315 (Scopus ID)
##### Funder
Swedish Research Council, 15339-91505-33Vinnova
##### Note

QC 20130927

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2017-12-06Bibliographically approved
3. Augmented-space cluster coherent potential approximation for binary random and short-range ordered alloys
Open this publication in new window or tab >>Augmented-space cluster coherent potential approximation for binary random and short-range ordered alloys
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 5, 054201- p.Article in journal (Refereed) Published
##### Abstract [en]

We use the earlier ideas of Razee and Prasad [Phys. Rev. B 45, 3265 (1992); Phys. Rev. B 48, 1349 (1993)], Datta [Phys. Rev. B 48, 8567 (1993)], and Mookerjee and Prasad [Phys. Rev. B 48, 17724 (1993)] to propose and implement a cluster generalization of the coherent potential approximation within a tight-binding linear muffin-tin orbital minimal basis set for binary alloys which are either random or have short-range order. In particular, we shall apply the technique to the CuZn alloys and compare it with other approaches.

##### Keyword
copper alloys, linear muffin-tin orbital method, tight-binding calculations, tin alloys
##### National Category
Metallurgy and Metallic Materials
##### Identifiers
urn:nbn:se:kth:diva-129337 (URN)10.1103/PhysRevB.79.054201 (DOI)000263815400033 ()
##### Note

QC 20130927

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2017-12-06Bibliographically approved
4. Study of optical response in disordered alloys using the generalized recursion in augmented space: Application to ferromagnetic FeCo alloy
Open this publication in new window or tab >>Study of optical response in disordered alloys using the generalized recursion in augmented space: Application to ferromagnetic FeCo alloy
2011 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 406, no 11, 2121-2125 p.Article in journal (Refereed) Published
##### Abstract [en]

We propose and briefly describe the generalized recursion in augmented space using a minimal TB-LMTO basis set for the calculation of configuration averaged current response functions in disordered binary alloys. Since disorder in the current terms is off-diagonal and non-separable, single-site mean-field approaches are unable to deal with it without further approximations. The augmented space approach is ideally suited for such situations and the generalized recursion proposed by Viswanath and Muller provides a fast and accurate O(N) technique for the actual calculations of the configuration averaged susceptibilities. We have applied the method to the disordered FeCo alloy. The results agree reasonably well with available experimental data on ordered versions of both the alloy systems, with extra broadening due to disorder induced lifetime effects.

##### Keyword
Optical properties, Random alloys, FeCo
##### National Category
Metallurgy and Metallic Materials
##### Identifiers
urn:nbn:se:kth:diva-129338 (URN)10.1016/j.physb.2011.03.005 (DOI)000290951200010 ()
##### Note

QC 20130927

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2017-12-06Bibliographically approved
5. First-principles study of atomic ordering in fcc Ni-Cr alloys
Open this publication in new window or tab >>First-principles study of atomic ordering in fcc Ni-Cr alloys
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 6, 064103- p.Article in journal (Refereed) Published
##### Abstract [en]

We investigate atomic ordering in fcc Ni-rich Ni-Cr alloys using first-principles techniques and statistical mechanics simulations based on the Ising Hamiltonian with effective cluster interactions computed by the screened generalized perturbation method (SGPM) and projector augmented wave (PAW) method. We demonstrate that effective chemical interactions in this system are quite sensitive to alloy composition and in fact to the specific configurational state. The chemical interactions for the high-temperature random state produce the atomic short-range order (SRO) with intensity maximum close to the (2/3 2/3 0) point of the reciprocal space in agreement with the previous first-principles investigation. A consistent with diffuse neutron scattering data maximum at the (1 1/2 0) position is obtained onlywhenwe take into consideration relatively small strain-induced interactions, which solves a long-standing inconsistency between theory and experiment in this system. The calculated transition temperature of order-disorder transition of Ni2Cr alloy, 880 K, is in good agreement with the experimental value of 863 K.

##### Keyword
Short-Range Order, Inhomogeneous Electron-Gas, Disordered Binary Alloys, At-Percent Cr, Molecular-Dynamics, Diffuse-Scattering, Lattice-Parameter, Potential Model, Solid-Solution, Monte-Carlo
##### National Category
Metallurgy and Metallic Materials
##### Identifiers
urn:nbn:se:kth:diva-129342 (URN)10.1103/PhysRevB.89.064103 (DOI)000332375400003 ()2-s2.0-84894694789 (Scopus ID)
##### Funder
Swedish Research Council, 15339-91505-33EU, European Research CouncilVinnova
##### Note

QC 20140331. Updated from manuscript to article in journal.

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2017-12-06Bibliographically approved
6. Finite tempreture elastic properties of B2-FeCo alloy: a first-principles study
Open this publication in new window or tab >>Finite tempreture elastic properties of B2-FeCo alloy: a first-principles study
##### National Category
Metallurgy and Metallic Materials
##### Identifiers
urn:nbn:se:kth:diva-129341 (URN)
##### Note

QS 2013

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2013-09-27Bibliographically approved

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Cite
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