|
| |
|
|
Studies of structural and magnetic properties of iron nanowires from first principles
Zelený, Martin ; Šob, Mojmír ; Hafner, J.
In this work we study the structure and stability of iron ultrathin free-standing nanowires by first-principles density functional approach. For total energy calculations, we use the Vienna ab initio Simulation Package (VASP) in the projector augmented-wave (PAW) representation. The evolution of electronic structure and magnetism of iron chains as a function of compression and stretch is investigated. The forming of different types of structures is analyzed: simple linear chain, dimerized chain, ideal two-dimensional (2D) zig-zag structure relaxed in x and y directions, fully relaxed 2D structure, and three-dimensional (3D) structure with tetrahedral arrangements. It turns out that the structure of iron nanowires and types of interatomic bonds are strongly dependent on their stretch or compression.
|
|
|
Studium tantalu pomocí potenciálů typu bond-order
Čák, Miroslav ; Mrověc, M. ; Vitek, V. ; Šob, Mojmír
We present a bond-order potential (BOP) study for the bcc transition metal tantalum. The BOPs are a real-space semiempirical scheme for the description of interatomic interactions based on the tight-binding approximation. The potentials are applied to the calculation of total energy profile along the tetragonal deformation path and gamma-surface of {110} plane. Our results are in a good agreement with the ab initio calculated values which indicates that BOPs are capable to describe properly the bonding in bcc transition metals.
|
|
| |
|
|
Elektronová struktura slitin india a cínu
Všianská, Monika ; Legut, Dominik ; Šob, Mojmír
The In-Sn system is interesting due to the existence of the simple hexagonal (sh) structure for compositions from 75 to 87 at% Sn at 25 ºC and from 73 to 85 at% Sn at -150 ºC. These alloys are usually referred to as gamma-Sn. Here we study the electronic structure and total energy of gamma-Sn with the help of virtual crystal approximation and demonstrate that sh structure has the lowest energy in the interval of existence of gamma-tin.
|
|
|
Studium magnetismu hranic zrn z prvních principů
Čák, Miroslav ; Šob, Mojmír ; Hafner, J.
Grain boundaries (GBs) represent an important class of two-dimensional extended defects in materials. Segregation of impurity atoms is responsible for a degradation of mechanical properties. Recently, it was found that application of magnetic annealing leads to decreasing concentration of impurities at GBs in Fe-0.8%Sn alloy and improves its ductility To understand the mechanism of this process it is necessary to study magnetism of clean GBs as well as of GBs with segregants at the microscopic (ab initio) level. In the present work, we investigate the Sigma5(310) GB in iron.
|
|
|
Stanovení kritické hodnoty pro šíření trhliny z ostrého v-vrubu
Majer, Zdeněk ; Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk
The aim of this paper is to investigate the beginnings of crack propagation from sharp V-notches. Stress distribution around the tip of a V-notch is described on the basis of linear-elastic fracture mechanics. The V-notch is a singular stress concentrator with a singularity exponent dependent on the V-notch opening angle. The stability criteria are generalized for a stress singularity different from 0,5. Using FEM analysis the critical stress for crack initiation was estimated as a function of the V-notch angle. The results of numerical calculations were compared with experiments taken from the literature.
|
|
|
Electronic structure In-Sn alloys
Všianská, Monika ; Legut, Dominik ; Šob, Mojmír
The InSn system is interesting by the existence of a simple hexagonal phase for compositions from 72 to 87 at% Sn at 25 °C and from 73 to 85 at% Sn at -150 °C. These alloys are usually referred to as gamma–Sn. The InSn alloys are disordered in the whole concentration interval. In this contribution, energetics and electronic structure of InSn system is studied from first principles. A simplified version of virtual crystal approximation is employed to describe disorder. It turns out that the present approach is capable of describing phase composition of InSn system in the whole concentration interval. In particular, we are able to reproduce the existence of simple hexagonal phase around 80 at% Sn.
|
|
| |
|
|
Tensile strength of alumina based ceramics foam
Řehořek, Lukáš ; Chlup, Zdeněk
In last years cellular materials are getting to focus of an interest in a number of industrial applications and science fields. These materials are often used for filtration of different mediums such as melts or in aerospace industry and even in tissue engineering. Hence, there is evolved effort to understand and describe mechanical and physical properties of these interesting materials. While behaviour of these materials in compression is well understand and published, tensile tests are not so frequent and concerning ceramic cellular materials they are highly rare. The methodology of evaluation of tensile properties of model ceramic foam material VUKAPOR((R))A used like filters in metallurgy was developed. This methodology is based on fixation of ceramic foam sample by specialised resin to a holder. Homogenous transfer of forces is ensured by this technique.
|
guest ::
