| 1. |
- Walls, B., et al.
(författare)
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Nanodomain structure of single crystalline nickel oxide
- 2021
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Ingår i: Scientific Reports. - : Nature Portfolio. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- In this work we present a comprehensive study of the domain structure of a nickel oxide single crystal grown by floating zone melting and suggest a correlation between point defects and the observed domain structure. The properties and structure of domains dictate the dynamics of resistive switching, water splitting and gas sensing, to name but a few. Investigating the correlation between point defects and domain structure can provide a deeper understanding of their formation and structure, which potentially allows one to tailor domain structure and the dynamics of the aforementioned applications. A range of inhomogeneities are observed by diffraction and microscopy techniques. X-ray and low-energy electron diffraction reveal domains on the submicron- and nanometer-scales, respectively. In turn, these domains are visualised by atomic force and scanning tunneling microscopy (STM), respectively. A comprehensive transmission electron microscopy (TEM) study reveals inhomogeneities ranging from domains of varying size, misorientation of domains, variation of the lattice constant and bending of lattice planes. X-ray photoelectron spectroscopy and electron energy-loss spectroscopy indicate the crystal is Ni deficient. Density functional theory calculations-considering the spatial and electronic disturbance induced by the favourable nickel vacancy-reveal a nanoscale distortion comparable to STM and TEM observations. The different inhomogeneities are understood in terms of the structural relaxation induced by ordering of nickel vacancies, which is predicted to be favourable.
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| 2. |
- Khvan, A. V., et al.
(författare)
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Thermodynamic properties of tin: Part I Experimental investigation, ab-initio modelling of alpha-, beta-phase and a thermodynamic description for pure metal in solid and liquid state from 0 K
- 2019
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Ingår i: Calphad. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0364-5916 .- 1873-2984. ; 65, s. 50-72
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic data for crystalline white and grey tin were assessed using an extended Einstein model from 0 K. Ab-initio simulations in the framework of density functional theory (DFT) with the quasiharmonic approximation (QHA) were carried out to define the heat capacities for both phases of tin from 0 K up to room temperatures. Good agreement was observed between theoretical and experimental heat capacities, which makes it possible to combine theoretical and experimental data to determine the standard entropies. Data for the liquid phase were described using a two state model. During the assessment, careful analysis of the experimental data was carried out. In order to fulfil the need for a precise evaluation of S-298(o) we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point and to estimate solid phase transition entropy and enthalpy which are difficult to measure due to a high activation barrier. Additional measurements of heat capacity were carried out where existing data were scarce.
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| 3. |
- Abrikosov, Igor, et al.
(författare)
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Theoretical description of pressure-induced phase transitions: a case study of Ti-V alloys
- 2015
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Ingår i: High Pressure Research. - : Taylor andamp; Francis: STM, Behavioural Science and Public Health Titles. - 0895-7959 .- 1477-2299. ; 35:1, s. 42-48
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Tidskriftsartikel (refereegranskat)abstract
- We discuss theoretical description of pressure-induced phase transitions by means of first-principles calculations in the framework of density functional theory. We illustrate applications of theoretical tools that allow one to take into account configurational and vibrational disorders, considering Ti-V alloys as a model system. The universality of the first-principles theory allows us to apply it in studies of different phenomena that occur in the Ti-V system upon compression. Besides the transitions between different crystal structures, we discuss isostructural transitions in bcc Ti-V alloys. Moreover, we present arguments for possible electronic transitions in this system, which may explain peculiar behaviour of elastic properties of V upon compression.
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| 4. |
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| 5. |
- Isaeva, E. I., et al.
(författare)
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Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl
- 2004
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 129:12, s. 809-814
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Tidskriftsartikel (refereegranskat)abstract
- The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering.
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| 6. |
- Yu Nikonov, A., et al.
(författare)
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Calculation of Mechanical Properties of BCC Ti-Nb Alloys
- 2015
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Ingår i: INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2015. - : AMER INST PHYSICS. - 9780735413306
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Konferensbidrag (refereegranskat)abstract
- We have calculated mechanical properties of bcc Ti-Nb alloys in the framework of the first-principles approach using the exact muffin-tin orbital method. The results obtained quantitatively correlate well with known experimental data and can be used in order to design new materials based on of Ti alloys intended for various applications, e.g. for bio-medical applications.
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| 7. |
- Abrikosov, I. A., et al.
(författare)
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Multiscale approach to theoretical simulations of materials for nuclear energy applications : Fe-Cr and Zr-based alloys
- 2013
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Ingår i: Advances in materials for nuclear energy. - : Materials Research Society. - 9781605114910 ; , s. 3-14
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Konferensbidrag (refereegranskat)abstract
- We review basic ideas behind state-of-the-art techniques for first-principles theoretical simulations of the phase stabilities and properties of alloys. We concentrate on methods that allow for an efficient treatment of compositional and thermal disorder effects. In particular, we present novel approach to evaluate free energy for strongly anharmonic systems. Theoretical tools are then employed in studies of two materials systems relevant for nuclear energy applications: Fe-Cr and Zr-based alloys. In particular, we investigate the effect of hydrostatic pressure and multicomponent alloying on the mixing enthalpy of Fe-Cr alloys, and show that in the ferromagnetic state both of them reduce the alloy stability at low Cr concentration. For Zr-Nb alloys, we demonstrate how microscopic parameters calculated from first-principles can be used in higher-level models.
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| 8. |
- Abrikosov, Igor, et al.
(författare)
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Theoretical Modeling of Thermodynamic and Mechanical Properties of the Pure Components of Ti and Zr Based Alloys Using the Exact Muffin-Tin Orbitals Method
- 2014
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Ingår i: Russian Physics Journal. - : Springer Verlag (Germany). - 1064-8887 .- 1573-9228. ; 56:9, s. 1030-1038
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Tidskriftsartikel (refereegranskat)abstract
- The exact muffin-tin orbitals (EMTO) method belongs to the third and latest generation of first-principles methods of calculating the electronic structure of materials in the so-called approximation of muffin-tin (MT) orbitals within the framework of the density functional theory. A study has been performed of its applicability for modeling the thermodynamic and mechanical properties of the pure components of Ti and Zr based alloys. The total energies of Ti, Zr, Nb, V, Mo, and Al are calculated in three crystal structures - face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP). For all of these elements and crystal structures, we have calculated the theoretical values of the lattice constants, elastic constants, and equations of state. The stable crystal structures have been determined. In all cases, calculations by the EMTO method predict the correct structure of the ground state. For stable structures we compared the obtained results with experiment and with calculations using full potential methods. We have demonstrated the reliability of the EMTO method and conclude that its further application for effective modeling of the properties of disordered alloys based on Ti and Zr is possible.
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| 9. |
- Chioncel, L., et al.
(författare)
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Ab initio electronic structure calculations of correlated systems : An EMTO-DMFT approach
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:23
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Tidskriftsartikel (refereegranskat)abstract
- We propose a self-consistent method for electronic structure calculations of correlated systems, which combines the local spin-density approximation (LSDA) and the dynamical mean field theory (DMFT). The LSDA part is based on the exact muffin-tin orbital approach, meanwhile the DMFT uses a perturbation scheme that includes the T matrix with fluctuation exchange approximation. The current LSDA+DMFT implementation fulfills both self-energy and charge self-consistency requirements. We present results on the electronic structure calculations for bulk 3d transition metals (Cr, Fe, and Ni) and for Fe/Cr magnetic multilayers. The latter demonstrates the importance of the correlation effects for the properties of magnetic heterostructures.
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| 10. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
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Defect-induced magnetic structure in (Ga1-xMnx)As
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 88:18, s. 187202-
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Tidskriftsartikel (refereegranskat)abstract
- We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga1-xMnx)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 (Ga1-xMnx)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.
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