National Repository of Grey Literature 11 records found  1 - 10next  jump to record: Search took 0.01 seconds. 
Polsterová, S. ; Všianská, Monika ; Friák, Martin ; Pizúrová, Naděžda ; Sokovnin, S. ; Šob, Mojmír
Motivated by our experimental research related to silver nanoparticles with various morphologies, we have employed quantum-mechanical calculations to provide our experiments with theoretical insight. We have computed properties of a 181-atom decahedral silver nanoparticle and two types of internal extended defects, -5(210) grain boundaries (GBs) and quadruple junctions (QJs) of these GBs. We have employed a supercell approach with periodic boundary conditions. Regarding the thermodynamic stability of the decahedral nanoparticle, its energy is higher than that of a defect-free face-centered cubic (fcc) Ag by 0.34 eV/atom. As far as the -5(210) GB is concerned, its energy amounts to 0.7 J/m2 and we predict that the studied GBs would locally expand the volume of the lattice. Importantly, the system with GBs is found rather close to the limit of mechanical stability. In particular, the computed value of the shear-related elastic constant C66 is as low as 9.4 GPa with the zero/negative value representing a mechanically unstable system. We thus predict that the -5(210) GBs may be prone to failure due to specific shearing deformation modes. The studied GBs have also the value of Poisson’s ratio for some loading directions close to zero. Next, we compare our results related solely to -5(210) GBs with those of a system where multiple intersecting -5(210) GBs form a network of quadruple junctions. The value of the critical elastic constant C66 is higher in this case, 13 GPa, and the mechanical stability is, therefore, better in the system with QJs.
Role of microscopic morphology in electrostatic charging of nanocrystalline diamond
Verveniotis, Elisseos ; Kromka, Alexander ; Rezek, Bohuslav
Self assembly of nanoparticles on NCD possible. Films macroscopically homogenous (SEM, Raman), however microsopic structural variations (SEM cross sections) do exist. Detailed KFM and CS-AFM measurements indicate that charge is mostly confined in the inter-grain space.
Electronic transport in intrinsic H-terminated nanocrystaline diamond with various grain size
Hubík, Pavel ; Mareš, Jiří J. ; Kozak, Halyna ; Kromka, Alexander ; Rezek, Bohuslav ; Krištofik, Jozef ; Kindl, Dobroslav
Both effective conductivity and Hall mobility of H-NCD were found to strongly decrease with the diminishing grain size. Effective Hall concentrations (to 1017 m-2) correspond to the true hole concentrations on the surface of the grain interiors. The effective Hall mobility is a robust parameter with respect to the surface conditions.
Autodifúze po hranicích v technickém niklu. 4. Vliv předžíhání vzorku
Rothová, Věra ; Svoboda, Milan ; Buršík, Jiří
Grain boundary self-diffusion in cast commercial purity nickel (99.5%) nickel was studied in the temperature range from 600 °C to 1000 °C. The relative grain orientation was analyzed on the same samples by means of electron backscatter diffraction (EBSD.
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.
Diffusion of Ni and Ga along High-Diffusivity Paths in polycrystalline Ni3Ga
Čermák, Jiří ; Rothová, Věra
The volume and grain boundary (GB) diffusion of 63Ni and 67Ga radiotracers in polycrystals of Ni3Ga intermetallic was studied in the vicinity of stoichiometric composition A3B (23.5 - 28.3 at. % Ga). Both volume- and GB diffusivity was measured in the temperature interval 773 - 1373 K by residual activity method. Obtained Ga volume diffusivity increases with increasing Ga concentration x(Ga); the increasing tendency of Ni volume diffusivity with increasing x(Ga) is pronounced especially at lower temperatures. GB diffusivity of both Ga and Ni in Ni3Ga are close one to another and contrary to diffusion behavior of components in Ni3Al - they do not show any significant dependence on x(Ga).
Application of ab initio electronic structure calculations to grain boundary structure
Šob, Mojmír ; Turek, Ilja ; Wang, L. G. ; Vitek, V.
State-of-the-art electronic structure methods are briefly characterized and their application to electronic structure of certain grain boundaries in tungsten and iron as well as to magnetic behaviour of Ru and Rh overlayers on the Ag(001) substrate is shown.
Properties of interfaces and plastic deformation in TiAl
Paidar, Václav
Complex plastic deformation of Ti-Al intermetallic alloys composed of lamellar microstructures is interpreted considering not only three forces acting on the carriers of plastic deformation but also the structure of these carries in the crystal lattice.
Effect of ordering on grain boundary segregation
Lejček, Pavel ; Schneeweiss, Oldřich
A simple phenomenological model of solute segregation at partially ordered grain boundaries is proposed and used to correlate complex concentration and temperature dependences of silicon segregation in ordered Fe-Si alloys.
Properties of interfaces and plastic deformation in TiAl
Paidar, Václav
Complex plastic deformation of TiAl intermetallic alloys composed of lamellar microstructure is interpreted considering not only the forces acting on the carriers of plastic deformation but also the structure of these carriers in the crystal lattice.

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