Papers by Keyword: Positron Lifetime

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Authors: M.F. Ferreira Marques, Paulo M. Gordo, C. Lopes Gil, Adriano P. de Lima, D. Placco Queiroz, Maria Norberta de Pinho, Z. Kajcsos, Gilles Duplâtre
Authors: R. Rajaraman, G. Amarendra, B. Viswanathan, K.P. Gopinathan
Authors: Masataka Mizuno, Hideki Araki, Yasuharu Shirai, Fumiyasu Oba, Isao Tanaka
Abstract: The formation of Mg vacancy induced by ultra-dilute trivalent impurities in MgO is investigated by a combination of positron lifetime measurements and first-principles calculations. The undoped MgO yields the shortest positron lifetime of 140 ps that is shorter than that of a single crystal sample. The positron lifetime of the doped samples increases with the increase of the Al dopant concentration and is saturated at around 180 ps. This result clearly indicates that the formation of Mg vacancy is induced by Al dopant. The concentration of the other trivalent impurities can be evaluated using the result of component analysis of positron lifetimes. The experimental bulk lifetime of 130 ps, which is obtained by employing trapping model, is well reproduced by the theoretical calculation using the semiconductor model. The calculated defect lifetime is about 20 ps longer than the experimental value. This may be due to the lattice relaxation around Mg vacancy associated with the trapping of positrons.
Authors: Yuriy S. Bordulev, Roman S. Laptev, Viktor N. Kudiiarov, Andrey M. Lider
Abstract: In this work the goal was to study the behavior of titanium-hydrogen system with hydrogen concentration of 1 wt. % at high temperature vacuum annealing by means of positron lifetime (PL) spectroscopy and electrical resistivity measurements. The range of hydrogen concentrations under investigation requires the γ phase formation. The study is related with the X-ray diffraction (XRD) and thermal desorption spectra (TDS) analysis. The registered positron lifetime spectra were analyzed by multiexponential decomposition into two components. Correlation of changes of the parameters of the PL spectrum and the electrical resistivity is revealed in this paper.
Authors: Andrey M. Lider, Olga V. Husaeva, Yuriy S. Bordulev, Roman S. Laptev, Viktor N. Kudiiarov
Abstract: This paper is devoted to the defect structure study of commercially pure titanium after hydrogen sorption-desorption cycles by means of positron lifetime (PL) and Doppler broadening spectrometry. Material was loaded with hydrogen from the gas phase till the concentration of hydrogen reached the value of 0.05 wt.% for each cycle. The essential changes in the positron annihilation characteristics of the sample are occurred after the each stage of treatment.
Authors: Roman S. Laptev, Andrey M. Lider, Yuriy S. Bordulev, Viktor N. Kudiiarov, Georgy V. Garanin, Wei Wang, Pavel V. Kuznetsov
Abstract: This paper presents the results of a defect structure investigation in commercially pure titanium alloy after hydrogen charging in a gaseous atmosphere at the temperature of 873 K up to the concentration of 5.1 at. %. Structure of samples was studied by positron lifetime, Doppler broadening and X-ray diffraction spectrometry. Several processes, corresponding to the different ranges of hydrogen concentrations were revealed. It was shown that hydrogen, penetrating in the material, expands its crystal lattice, initiates formation of vacancy-like defects of different dimensions and reacts with the last ones, forming the defect-hydrogen complexes.
Authors: Ryoichi Suzuki, Yoshinori Kobayashi, Tomohisa Mikado, Hideaki Ohgaki, M. Chiwaki, T. Yamazaki, T. Tomimasu
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