Positron annihilation studies of some anomalous features of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Ni</mml:mi><mml:msub><mml:mi mathvariant="normal">Fe</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math>nanocrystals grown in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Si</mml:mi><mml

Chakraverty, S.; Mitra, Subrata; Mandal, Kalyan; Nambissan, P.M.G.; Chattopadhyay, Sanatan

doi:10.1103/physrevb.71.024115

Cited by 113 publications

(79 citation statements)

References 25 publications

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“…It is interesting that accordingly to available experimental data on positron annihilation in other spinel ferrite nanopowders of the same range of grain sizes the reduced bulk components have been observed [20][21][22][23][24]. It should be noted that in our measurements the samples containing free-flowing powders were used whilst in the cited papers compacted powder had been studied.…”

Section: Resultsmentioning

confidence: 99%

Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

et al. 2017

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Nanosized iron oxide powders are materials considered with regard to its application in medical therapy called hyperthermia. Magnetite nanopowders with crystallite size varying from 6.6 to 11.8 nm have been prepared by the co-precipitation method. In this study a change of a crystallite size is driven mainly by varying of initial pH of water ammonia solution in which a process of magnetite precipitation runs. Crystallographic structures and phase composition obtained samples and the size of magnetite nanoparticles were determined by X-ray diffraction method. Positron lifetime spectroscopy has been used to assess defectiveness of microstructure. Experimental positron annihilation spectra were successfully resolved into three lifetime components. It appears that from point of view of microstructure the defects concentrations in studied nanopowder samples are very high which causes a saturation of positron trapping.

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Section: Resultsmentioning

confidence: 99%

Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

et al. 2017

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“…As was described in [18], the component with defectrelated τ int lifetime can reflect positron trapping sites caused by water. Under accepted prerequisites, these extended defects can be associated with pseudogap voids at the interface between the outer surface layer of agglomerated nanoparticles and innermost layer of surrounding initial matrix (as it well demonstrated in [24,25]). The bulk positron lifetime can now be attributed to bulk positron lifetime of nanoparticle agglomerate.…”

Section: Resultsmentioning

confidence: 99%

Water-Sorption Effects near Grain Boundaries in Modified MgO-Al₂O₃ Ceramics Tested with Positron-Positronium Trapping Algorithm

et al. 2018

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Water-sorption processes near grain boundaries in the MgO-Al2O3 ceramics prepared at different temperatures were studied using positron annihilation lifetime spectroscopy. Numerical values of three-and four-component treatment of spectra were used for study of physical-and chemical-sorption processes in the MgO-Al2O3 ceramics. To apply mathematical approach in the form of positron-positronium trapping algorithm into three-component treatment of positron annihilation lifetime spectra it was shown that physical-adsorbed water did not modify positron trapping sites near grain boundaries in water-immersed MgO-Al2O3 ceramics and localized mainly in nanopores. The chemically-adsorbed water modifies structural extended defects located near grain boundaries that accompanied them by void fragmentation at water desorption.

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“…From PALS analysis, the lifetime and intensity relating to positron free annihilation in the non-defective nanocrystalline grain volumes were derived for analogous NiFe 2 O 4 (SiO 2 ) composite obtained by sol-gel method [16,17]. The lifetime, denoted by authors as  n , is equal to about 0.14 ns.…”

Section: Resultsmentioning

confidence: 99%

Study on the effect of atmospheric gases adsorbed in MnFe₂O₄/MCM-41 nanocomposite on ortho-positronium annihilation

et al. 2015

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In this paper, results of positron annihilation lifetime spectroscopy (PALS) studies of MnFe2O4/MCM-41 nanocomposites in N2 and O2 atmosphere have been presented. In particular, the influence of manganese ferrite loading and gas filling on pick-off ortho-positronium (o-Ps) annihilation processes in the investigated samples was a point of interest. Disappearance of the longest-lived o-Ps component with τ5 present in the PAL spectrum of initial MCM-41 mesoporous material in the PAL spectra of MnFe2O4-impregnated MCM-41 measured in vacuum is a result of either a strong chemical o-Ps quenching or the Ps inhibition effects. The intensity I4 of the medium-lived component initially increases, reaching a maximum value for the sample with minimum manganese ferrite content, and then decreases monotonically. Analogous dependence for the intensity I3 of the shortest-lived component shows a maximum at higher MnFe2O4 content. Filling of open pores present in the studied nanocomposites by N2 or O2 at ambient pressure causes partial reappearance of the τ4 and τ5 components, except a sample with maximum ferrite content. The lifetimes of these components measured in O2 are shortened in comparison to that observed in N2 because of paramagnetic quenching. Anti-inhibition and anti-quenching effects of atmospheric gases observed in the MnFe2O4/MCM-41 samples are a result of neutralization of some surface active centers acting as inhibitors and weakening of pick-off annihilation mechanism, respectively.

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Positron annihilation studies of some anomalous features ofNiFe2O4nanocrystals grown inSi

Cited by 113 publications

References 25 publications

Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

Water-Sorption Effects near Grain Boundaries in Modified MgO-Al₂O₃ Ceramics Tested with Positron-Positronium Trapping Algorithm

Study on the effect of atmospheric gases adsorbed in MnFe₂O₄/MCM-41 nanocomposite on ortho-positronium annihilation

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Positron annihilation studies of some anomalous features ofNiFe2O4nanocrystals grown inSi

Cited by 113 publications

References 25 publications

Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

Positron Annihilation in Magnetite Nanopowders Prepared by Co-Precipitation Method

Water-Sorption Effects near Grain Boundaries in Modified MgO-Al2O3 Ceramics Tested with Positron-Positronium Trapping Algorithm

Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation

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Water-Sorption Effects near Grain Boundaries in Modified MgO-Al₂O₃ Ceramics Tested with Positron-Positronium Trapping Algorithm

Study on the effect of atmospheric gases adsorbed in MnFe₂O₄/MCM-41 nanocomposite on ortho-positronium annihilation