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Calculation of Positron Response from Embedded Nanoparticles

100%
Kuriplach J.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
784-791
EN
Nanoparticles embedded in a matrix can trap positrons under certain conditions. In such cases nanoparticles can be effectively studied by means of positron annihilation because positron annihilation characteristics contain information related to nanoparticles' electronic and atomic structure. Of great importance is to calculate the positron response from such nanoparticles. Then, nanoparticles can, in principle, be identified by comparing the measured and calculated positron annihilation response. For this purpose we present an efficient computational method based on the well-known atomic superposition technique. This method is explained in detail, justified on the basis of first principles calculations, and applied to Cu nanoparticles embedded in the Fe matrix.
2
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Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons

100%
Kuriplach J.
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vol. 125
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issue 3
722-725
EN
Vacancy behavior and positron trapping at selected grain boundaries in iron, nickel, and zirconia are investigated theoretically. It is found that the grain boundary vacancy loses its free volume in metals at moderate temperatures whereas it is kept up to very high temperatures in zirconia. The consequences of these findings for positron annihilation studies of nanocrystalline materials are discussed.
3
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Calculation of Free Volume in Computer Generated Grain Boundaries

63%
Van Petegem S., Kuriplach J.
Acta Physica Polonica A
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2005
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vol. 107
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issue 5
769-775
EN
We investigate the positron lifetime distribution in grain boundaries originating from computer generated nanocrystalline configurations. We give a brief overview of the computational methods and we discuss the influence of thermal vibrations and grain size on the obtained positron lifetime distributions.
4
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Preferential Positron Annihilation in Binary Alloys

51%
Kuriplach J., Dryzek E., Dryzek J., Šob M.
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vol. 95
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issue 4
605-611
EN
The effect of preferential positron annihilation at individual constituent atoms in binary alloys is examined theoretically and experimentally. In particular, the results of recently studied alloys Fe-Al and Mg-Cd together with new preliminary results for the Sn-In system are discussed and summarised. In the case of the Sn-In system, the concentration dependencies of positron annihilation rates and Doppler broadening spectra are analysed.
5
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Positron Lifetimes in Zirconia-Based Nanomaterials

39%
Procházka I., Čížek J., Kuriplach J., Melikhova O., Konstantinova T., Danilenko I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1495-1499
EN
Positron lifetime spectroscopy is employed in a comparative study of several zirconia-based materials: (i) the pressure-compacted nanopowders of the three zirconia polymorphs - pure ZrO_2 (monoclinic), yttria-stabilized ZrO_2+3 mol.% Y_2O_3 (tetragonal) and yttria-stabilized ZrO_2+8 mol.% Y_2O_3 (cubic), (ii) ceramic materials obtained by sintering of the above two yttria-stabilized zirconia nanopowders and (iii) the tetragonal and cubic yttria-stabilized zirconia monocrystals. Positron lifetime data observed on the nanopowders suggest that the two shortest components, exhibiting lifetimes of ≈180 and ≈370 ps, arise from the annihilation of positrons trapped in defects associated with grain boundaries, presumably the vacancy-like defects and tripple points, respectively. Positron lifetime spectra observed on the ceramic materials resemble those found for the corresponding monocrystals, giving thus an additional support to the above interpretation of the nanopowders results.
6
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Simulation of Positron Annihilation Response to Mechanical Deformation of Nanostructured AgCo

39%
Melikhova O., Kuriplach J., Čížek J., Procházka I., Hou M., Pisov S., Zhurkin E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1455-1464
EN
Nanostructured materials attract nowadays a broad attention due to their specific properties. Defects play an essential role in material properties so their characterisation is very important. The evolution of the various open volume defects in AgCo nanowire modelled samples obtained using molecular dynamics was studied. Isothermal and isoenergetic deformation mechanisms are considered. General analyses of open volume defects concerning their size and their chemical environment were performed. Positron lifetimes, binding energies, and high momentum parts of the momentum distribution of annihilationγ-quanta were calculated for selected defects.
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