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    Wyświetlanie 1-4 z 4
    Tytuł:
    Hydrogen-Induced Defects in Palladium
    Autorzy:
    Melikhova, O.
    Čížek, J.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1338026.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.-y
    Opis:
    In the present work positron annihilation spectroscopy was employed for investigation of hydrogen-induced defects in Pd. Well annealed Pd samples were electrochemically charged with hydrogen and development of defects with increasing hydrogen concentration $x_{H}$ was investigated. At low concentrations (α-phase, $x_{H}$ < 0.017 H/Pd) hydrogen loading introduced vacancies, since absorbed hydrogen segregating at vacancies lowers remarkably the vacancy formation energy. When hydrogen concentration exceeds 0.017 H/Pd, particles of palladium hydride (PdH) are formed. Stress induced by growing PdH particles leads to plastic deformation which generates dislocations and vacancies in the sample.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 752-755
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hydrogen Interaction with Vacancies in Electron Irradiated Niobium
    Autorzy:
    Čižek, J.
    Procházka, I.
    Brauer, G.
    Anwand, W.
    Gemma, R.
    Nikitin, E.
    Kirchheim, R.
    Pundt, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812478.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.-y
    Opis:
    Defect studies of Nb irradiated with 10 MeV electrons were performed in the present work by means of positron annihilation spectroscopy. The lattice defects were characterized by positron lifetime spectroscopy. Moreover, defect depth profiles were studied by slow positron implantation spectroscopy. The experimental investigations were accompanied by first principles theoretical calculations of positron parameters. It was found that irradiation-induced vacancies in Nb specimens are surrounded by H, which causes a shortening of the lifetime of trapped positrons. The influence of a Pd and Cr over-layer on the H concentration in the Nb specimens was examined.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1293-1299
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy
    Autorzy:
    Αda, P.
    Cieslar, M.
    Vostrý, P.
    Bečvář, F.
    Νovotný, I.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933483.pdf
    Data publikacji:
    1995-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.72.-y
    78.70.-g
    81.40.-z
    Opis:
    Decomposition of the supersaturated solid solution of 2 at.% Cu in Al was investigated by means of electrical resistivity and high-resolution positron lifetime measurements. The phase composition of this alloy was determined by transmission electron microscopy. Electrical resistivity measurements were performed by a classical four-point method. Positron lifetime spectra were measured by means of a spectrometer consisting of two BaF$\text{}_{2}$ detectors and a standard fast-slow coincidence system. The specimens were first exposed to the solution heat treatment at 783 K for 19 hours with a subsequent quenching. Then the specimens were isochronally annealed in the temperature range 293 ÷ 573 K. Annealing responses of electrical resistivity and positron annihilation were studied. Resistivity measurements as well as transmission electron microscopy observations confirmed the well-known decomposition sequence of the Al-Cu alloy. The decomposition of the alloy was manifested by the decrease in the intensity of positron lifetime component τ$\text{}_{2}$ = (207 ±2 ) ps correlated with simultaneous appearance and increase in the intensity of τ$\text{}_{3}$ = (180 ± 5) ps component. Component τ$\text{}_{2}$ originates from positron annihilation in vacancies trapped at the Guinier-Preston zones while τ$\text{}_{3}$ comes from annihilation of the positrons localized in the misfit dislocations at coherent precipitates of the Al$\text{}_{2}$Cu phase. The shortest observed component τ$\text{}_{1}$ apparently belongs to annihilation of untrapped positrons.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 1; 111-117
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Defects in Ultra-Fine Grained Mg and Mg-Based Alloys Prepared by High Pressure Torsion Studied by Positron Annihilation
    Autorzy:
    Čížek, J.
    Procházka, I.
    Smola, B.
    Stulíková, I.
    Kužel, R.
    Matěj, Z.
    Cherkaska, V.
    Islamgaliev, R.
    Kulyasova, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043304.pdf
    Data publikacji:
    2005-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    79.60.Jv
    61.72.-y
    Opis:
    Despite the favourable strength and thermal stability, a disadvantage of the Mg-based alloys consists in a low ductility. Recently it has been demonstrated that ultra fine grained metals with grain size around 100 nm can be produced by high pressure torsion. A number of ultra fine grained metals exhibit favourable mechanical properties consisting in a combination of a very high strength and a significant ductility. For this reason, it is highly interesting to examine microstructure and physical properties of ultra fine grained Mg-based light alloys. Following this purpose, microstructure investigations and defect studies of ultra fine grained pure Mg and ultra fine grained Mg-10%Gd alloy prepared by high pressure torsion were performed in the present work using positron annihilation spectroscopy combined with X-ray diffraction, TEM observations, and microhardness measurements. Positrons are trapped at dislocations in Mg and Mg-10%Gd alloy deformed by high pressure torsion. A number of dislocations increases with the radial distance r from the centre to the margin of the sample. No microvoids (small vacancy clusters) were detected. Mg-10%Gd alloy deformed by high pressure torsion exhibits a homogeneous ultra fine grained structure with a grain size around 100 nm and high dislocations density. On the other hand, pure Mg deformed by high pressure torsion exhibits a binomial type of structure which consists of "deformed regions" with ultra fine grained structure and a high dislocation density and dislocation-free "recovered regions" with large grains. It indicates a dynamic recovery of microstructure during high pressure torsion processing.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 5; 738-744
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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