Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

Das, Anjan; Mandal, Atis Chandra; Roy, Soma; Prashanth, P. N.; Ahamed, Sk Izaz; Kar, S.; Prasad, Mithun S.; Nambissan, P.M.G.

doi:10.1016/j.physe.2016.03.032

Cited by 20 publications

(6 citation statements)

References 30 publications

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“…The peak at p L = 10 × 10 −3 m 0 c is due to positron annihilation with the electrons in the 2p orbital of oxygen ions. [40] The curves indicate reduced annihilation in defects in samples prepared at 400 • C and 450 • C. It supports the findings of the positron lifetime measurements and is more vividly displayed by the variations of the S and W line-shape parameters. These parameters are respectively estimated as the ratio of events under ∆E = ±0.00058 MeV and jointly under ∆E = ±0.00203 to ±0.00319 MeV of the projected onedimensional spectra to the total events under it.…”

Section: Coincidence Doppler Broadening Measurementssupporting

confidence: 83%

“…The value of E g and its changes with crystallite sizes are identical in nature and magnitude to the changes expected in the event of quantum confinement effects, which are expected and have been observed in certain other nanocrystalline systems earlier. [38][39][40][41] For example, the exciton Bohr radius the case of PbS nanocrystallites is 18 nm, [42] which means the band gap energies [43,44] would show a definite increase in crystallites of sizes 36 nm and below. Assuming that a similar value holds good for PbO nanocrystallites, the present results agree with the onset of similar effects.…”

Section: -3mentioning

confidence: 99%

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Characterization, spectroscopic investigation of defects by positron annihilation, and possible application of synthesized PbO nanoparticles*

Ali

Das²,

Agrawal

et al. 2021

Chinese Phys. B

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Nanocrystalline samples of highly pure lead oxide were prepared by the sol-gel route of synthesis. X-ray diffraction and transmission electron microscopic techniques confirmed the nanocrystallinity of the samples, and the average sizes of the crystallites were found within 20 nm to 35 nm. The nanocrystallites exhibited specific anomalous properties, among which a prominent one is the increased lattice parameters and unit cell volumes. The optical band gaps also increased when the nanocrystallites became smaller in size. The latter aspect is attributable to the onset of quantum confinement effects, as seen in a few other metal oxide nanoparticles. Positron annihilation was employed to study the vacancy type defects, which were abundant in the samples and played crucial roles in modulating their properties. The defect concentrations were significantly larger in the samples of smaller crystallite sizes. The results suggested the feasibility of tailoring the properties of lead oxide nanocrystallites for technological applications, such as using lead oxide nanoparticles in batteries for better performance in discharge rate and resistance. It also provided the physical insight into the structural build-up process when crystallites were formed with a finite number of atoms, whose distributions were governed by the site stabilization energy.

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Section: Coincidence Doppler Broadening Measurementssupporting

confidence: 83%

Section: -3mentioning

confidence: 99%

Characterization, spectroscopic investigation of defects by positron annihilation, and possible application of synthesized PbO nanoparticles*

Ali

Das²,

Agrawal

et al. 2021

Chinese Phys. B

Self Cite

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“…The ratio curves generated from the CDB spectra of all the samples following the procedure described by Asoka-Kumar et al and using annealed single crystalline Al (of purity 99.999%) as the reference material are shown in Figure . The characteristic peak at the electron momentum p L = 9.8 × 10 –3 m o c is due to positron annihilation by the 2p electrons of oxygen environment surrounding the cation (Zn) monovacancies and is usually observed in wide band gap metal oxide semiconductors. ,,− In other words, positrons are mainly trapped in vacancies generated by the absence of Zn 2+ ions or its clusters. A report that discusses the annihilation of positrons at the negatively charged Zn 2+ vacancies in ZnO confirms it with the corresponding CDB spectra of CdO, NiO and Zn metal .…”

Section: Results and Discussionmentioning

confidence: 99%

Diverse Spectroscopic Studies and First-Principles Investigations of the Zinc Vacancy Mediated Ferromagnetism in Mn-Doped ZnO Nanoparticles

Ponnusamy

Selvaraj

Ramachandran

et al. 2016

Crystal Growth & Design

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A systematic study on the room temperature ferromagnetism (RTFM) in undoped and Mn-doped ZnO nanoparticles (NPs) prepared by the coprecipitation method has been reported. The neutral and singly ionized zinc vacancy defects exhibited in the results of photoluminescence (PL), micro-Raman spectroscopy, and electron paramagnetic resonance (EPR) studies are found to be of ferromagnetic origin in bare ZnO, and it has been confirmed that Mn2+ ions substitutionally enter at Zn2+ sites in wurtzite ZnO. The results of positron annihilation and coincidence Doppler broadening measurements corroborate the Zn vacancies and their clusters. It is observed that in Mn:ZnO, the magnetic ordering is changed from ferro- to paramagnetic because of interacting adjacent Mn–Mn ions. The higher saturation magnetization of 565 × 10–3 emu/g is explained by a quasi indirect exchange mechanism based on the interaction of bound magnetic polarons formed by the Zn vacancies (V Zn) and nearby Mn ions. Further, first principle calculations reveal the magnetic centers in nonmagnetic ZnO with V Zn and the stable ferromagnetic ordering in Mn:ZnO at the optimum distance of Mn–Mn ≈ 3.26 Å.

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“…In an earlier work on Cd-substituted ZnO nanocrystals by Ghosh et al [13], strain-induced inhomogeneity had been found to lead to phase segregation of CdO from Zn 1-x Cd x O beyond a certain concentration. The studies earlier reported on a number of wide bandgap semiconductors, such as ZnO, NiO, TiO 2 , MgO, PbO, SnO 2 etc, also had met with similar restrictions owing to phase segregation of individual oxides beyond x = 0.2-0.3 [14][15][16][17][18][19]. The work by Ghosh et al [13] had in fact reported on the effects of doping Cd in ZnO but upto a concentration of x = 0.09.…”

Section: Introductionmentioning

confidence: 93%

Defect analysis and microstructural characterization of zinc-substituted cadmium oxide nanocrystallites by positron annihilation and supplementary methods

Ahmed,

Mukherjee,

Singha

et al. 2023

Phys. Scr.

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Pure and zinc-doped cadmium oxide nanocrystallites of sizes in the range 25 nm to 16 nm are synthesized by adopting a chemical precipitation method and by varying the doping concentration from 0.0 to 0.25 at.%. The decrease in nanocrystallite sizes with increasing substitution is expected from the smaller ionic radii of Zn2+. But more revealing is the interfacial defects formation at higher concentration of doping, which is attributed to the dissimilar crystalline structure of ZnO and CdO. X-ray diffraction patterns show well defined peaks and additional characterisation is done through transmission electron microscopy. The optical band gap measurements indicate the dominance of substitution-induced disorder over the confinement of excitons, leading to a decrease in the band gap energies. The results of positron annihilation studies confirm the cancellation of the existing vacancy type defects in the initial stage, followed by the substitution. Photoluminescence spectra reveal the distinct peaks of optical plasmonic excitations and the defect population in the bandgap and the intensity variations agreed with that of the defect related positron annihilation intensity. The segregation of ZnO phase leading to the formation of interfacial boundaries is found as a strong deterrent against the success of continued substitution.

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Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

Cited by 20 publications

References 30 publications

Characterization, spectroscopic investigation of defects by positron annihilation, and possible application of synthesized PbO nanoparticles*

Characterization, spectroscopic investigation of defects by positron annihilation, and possible application of synthesized PbO nanoparticles*

Diverse Spectroscopic Studies and First-Principles Investigations of the Zinc Vacancy Mediated Ferromagnetism in Mn-Doped ZnO Nanoparticles

Defect analysis and microstructural characterization of zinc-substituted cadmium oxide nanocrystallites by positron annihilation and supplementary methods

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