Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies |
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| Affiliation: | 1. Department of Physics, A.P.C. Roy Government College, Siliguri, Darjeeling 734010, West Bengal, India;2. Department of Physics, University of Burdwan, Golapbag, Burdwan 713104, West Bengal, India;3. Applied Nuclear Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064, India;1. AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków, Poland;2. AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, al. Mickiewicza 30, Kraków, Poland;1. Departamento de Física e Química, Universidade Estadual Paulista, 15385-000 Ilha Solteira, São Paulo, Brazil;2. Instituto de Geociências e Ciências Exatas – IGCE, Universidade Estadual Paulista, Departamento de Física, 13506-970 Rio Claro, São Paulo, Brazil;3. Instituto de Física, Universidade Federal Fluminense, 24210-340 Niterói, RJ, Brazil;1. Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Chihuahua/Monterrey, 120 Avenida Miguel de Cervantes, 31109 Chihuahua, Mexico;2. Centro de Investigación y de Estudios Avanzados del IPN (CINVESTAV) Querétaro, Libramiento Norponiente 2000, Fracc. Real de Juriquilla, 76230 Querétaro, Mexico;3. Chernivtsi National University, Kotsyubynsky Str. 2, 58012 Chernivtsi, Ukraine;1. Instituto de Física, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín, Colombia;2. Instituto de Física, Universidade Federal de Alagoas, Maceió-AL 57072-970, Brazil;3. Instituto de Física, Universidade Estadual de Campinas - Unicamp, Campinas - SP 13083-859, Brazil;1. Chemical Engineering Faculty, Sahand University of Technology, P.O. Box 51335-1996, Sahand New Town, Tabriz, Iran;2. Reactor and Catalysis Research Center (RCRC), Sahand University of Technology, P.O. Box 51335-1996, Sahand New Town, Tabriz, Iran;3. Nanostructure Material Research Center (NMRC), Sahand University of Technology, P.O. Box 51335-1996, Sahand New Town, Tabriz, Iran |
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| Abstract: | Magnesium oxide nanocrystallites exhibit certain abnormal characteristics when compared to those of other wide band gap oxide semiconductors in the sense they are most prone to water absorption and formation of a hydroxide layer on the surface. The problem can be rectified by heating and pure nanocrystallites can be synthesized with controllable sizes. Inevitably the defect properties are distinctly divided between two stages, the one with the hydroxide layer (region I) and the other after the removal of the layer by annealing (region II). The lattice parameters, the optical band gap and even the positron annihilation characteristics are conspicuous by their distinct behavior in the two stages of the surface configurations of nanoparticles. While region I was specific with the formation of positronium-hydrogen complexes that drastically altered the defect-specific positron lifetimes, pick-off annihilation of orthopositronium atoms marked region II. The vacancy clusters within the nanocrystallites also trapped positrons. They agglomerated due to the effect of the higher temperatures and resulted in the growth of the nanocrystallites. The coincidence Doppler broadening spectroscopic measurements supported these findings and all the more indicated the trapping of positrons additionally into the neutral divacancies and negatively charged trivacancies. This is apart from the Mg2+ monovacancies which acted as the dominant trapping centers for positrons. |
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| Keywords: | Defects Nanocrystals Magnesium oxide Optical absorption Positron annihilation Vacancy clusters |
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