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Thermophysical properties of paramagnetic Fe from first principles
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. National University of Science and Technology, Russia.ORCID iD: 0000-0002-9920-5393
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 22, article id 224406Article in journal (Refereed) Published
Abstract [en]

A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of alpha-, gamma-, and delta-iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of gamma- and delta-iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for alpha- and delta-Fe and about 30% for gamma-Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013)]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of gamma- and delta-iron.

Place, publisher, year, edition, pages
American Physical Society, 2017. Vol. 96, no 22, article id 224406
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-220460DOI: 10.1103/PhysRevB.96.224406ISI: 000417075100001Scopus ID: 2-s2.0-85039421203OAI: oai:DiVA.org:kth-220460DiVA, id: diva2:1170409
Funder
VINNOVASwedish National Infrastructure for Computing (SNIC), 2015/16-50
Note

QC 20180103

Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-02-27Bibliographically approved
In thesis
1. Finite temperature properties of elements and alloy phases from first principles
Open this publication in new window or tab >>Finite temperature properties of elements and alloy phases from first principles
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

First principles calculations are usually concerned with properties calculated at temperature 0 K. However, the industrially important materials are functioning at finite temperatures. To fill such a gap a first-principles based modeling of free energy has been developed in this thesis and finite temperature properties of different phases of Fe and Mn have been calculated and contrasted with available experimental data.

In particular, using partitioning of the Helmholtz free energy, thermophysical properties of paramagnetic Fe have been reported. The heat capacity, lattice constant, thermal expansion and elastic moduli of γ- and δ-Fe show a good agreement with available experimental data. In the case of α-Fe, we observe a good agreement for elastic moduli and thermal expansion with experiments but the heat capacity is not well-reproduced in the calculations because of the large contribution of magnetic short-range which our models are not capable of capturing.

α- and β-Mn theoretically pose a challenge for direct simulations of thermodynamic properties because of the complexity of magnetic and crystal structure. The partitioning of free energy has been used and thermodynamics of these phases have been derived. The obtained results show a good agreement with experimental data suggesting that, despite the complexities of these phases, a rather simple approach can well describe their finite temperature properties. High temperature phases of Mn, γ and δ, are also theoretically challenging problems. Employing a similar approach to Fe, thermophysical properties of these high symmetry phases of Mn have been reported which also show good agreement with available experimental data.

The point defect and metal-self diffusion in titanium carbide (TiC), a refractory material, have been investigated in the present work. The common picture of metal-vacancy exchange mechanism for metal self-diffusion was shown to be unable to explain the experimentally observed values of activation energy. Several new clusters of point defects such as vacancies and interstitials have been found and reported which are energetically lower that a single metal vacancy. In a subsequent study, we showed that some of these clusters can be considered as mediators of metal self-diffusion in TiC.

Evaluation of structural properties of Ti(O,C), a solid solution of TiC and β-TiO, from supercell approach is an extremely difficult task. For a dilute concentration of O, we show the complexity of describing an impurity of O in TiC using supercell approach. A single-site method such as the exact muffin-tin orbital method in the coherent potential approximation (EMTO-CPA) is a good alternative to supercell modeling of Ti(O,C). However, a study of Ti(O,C) using EMTO-CPA requires a further development of the technique regarding the partitioning of space. The shape module of EMTO has been modified for this purpose. With the help of the modified module, Ti(O,C) have been studied using EMTO-CPA. The results for the divacancy concentration and corresponding lattice parameter variations show good agreement with experimental data.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 78
National Category
Condensed Matter Physics
Research subject
Materials Science and Engineering; Physics
Identifiers
urn:nbn:se:kth:diva-223668 (URN)978-91-7729-687-4 (ISBN)
Public defence
2018-03-26, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
VINNOVA
Note

QC 20180228

Available from: 2018-02-28 Created: 2018-02-27 Last updated: 2018-03-08Bibliographically approved

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Ehteshami, HosseinKorzhavyi, Pavel A.

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