PAL spectroscopy in application to humidity-sensitive MgAl2O4 ceramics

Shpotyuk, O.; Ingram, Adam; Klym, Halyna; Vakiv, M.; Hadzaman, I.; Filipecki, J.

doi:10.1016/j.jeurceramsoc.2005.03.174

Cited by 38 publications

(21 citation statements)

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“…It was shown that in the case of ceramics these data were determined mainly by crystallographical features of individual grains, while structural disturbances due to intergranular contacts within ceramics were a subject for additional complications [2][3][4]7]. That is why the measured positron lifetime spectra for sintered ceramics can be adequately explained within a unified multi-channel positron annihilation model involving discrete positron trapping and ortho-positronium (oPs) decay modes, the best fitting being achieved using at least 3 independent components in the resolved lifetime spectra (two for positron trapping and one for o-Ps decaying) [2][3][4]8]. In terms of this model, the second positron trapping component with τ 2 = 0.3-0.5 ns lifetimes is attributed to free-volume defects such as neutral or negatively-charged vacancies especially near grain boundaries.…”

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confidence: 99%

Defect characterization methodology in sintered functional spinels with PALS technique

Balitska

Filipecki

Ingram

et al. 2007

Phys. Status Solidi (c)

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It is shown that extended free-volume defects in sintered functional spinels can be well characterized with positron annihilation lifetime spectroscopy, provided obtained data are treated in terms of unified multichannel positron annihilation model involving both positron trapping and ortho-positronium decay modes. Crystallographical specificity of spinel structure reflects in the shortest lifetime component, while the middle component corresponds to vacancy-like defects near grain boundaries.1 Introduction Sintered spinel-type ceramics have been widely used as one of the most perspective materials for multifunctional device application [1][2][3][4][5]. Because of significant complications in the structure of these ceramics revealed at the levels of individual grains, intergrain boundaries and pores [6], the further progress in this field is dependent to a great extent on the development of new characterization techniques, which can be used in addition to traditional ones. This concerns, in part, the positron annihilation lifetime spectroscopy (PALS), the method only recently applied to fine-grained powders and ceramics [7].In general, the PALS being it sensitive to low electron density reflects a so-called void-species distribution within structural network of solids [7]. But meaningful interpretation of PALS data is well reliable only for some types of crystals. It was shown that in the case of ceramics these data were determined mainly by crystallographical features of individual grains, while structural disturbances due to intergranular contacts within ceramics were a subject for additional complications [2][3][4]7]. That is why the measured positron lifetime spectra for sintered ceramics can be adequately explained within a unified multi-channel positron annihilation model involving discrete positron trapping and ortho-positronium (oPs) decay modes, the best fitting being achieved using at least 3 independent components in the resolved lifetime spectra (two for positron trapping and one for o-Ps decaying) [2][3][4]8]. In terms of this model, the second positron trapping component with τ 2 = 0.3-0.5 ns lifetimes is attributed to free-volume defects such as neutral or negatively-charged vacancies especially near grain boundaries. The shortest component named the reduced bulk positron lifetime τ 1 is mainly due to annihilation in defect-free bulk with small mixing from other positron trapping channels. The largest component at the level of a few nanoseconds is responsible for a so-called o-Ps "pick-off" annihilation [7].

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confidence: 99%

Defect characterization methodology in sintered functional spinels with PALS technique

Balitska

Filipecki

Ingram

et al. 2007

Phys. Status Solidi (c)

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“…Taking into account the model described in [16,22,23], the shortest lifetime component in the studied ceramics reflects mainly the microstructure specificity of the spinel with character octahedral and tetrahedral cation vacancies. It is shown (see Table 2) that the lifetime τ 1 of this first component and intensity I 1 are not practically changed with T s .…”

Section: Resultsmentioning

confidence: 99%

“…PALS measurements were performed with an ORTEC spectrometer based on 22 Na source placed between two ceramic samples ( Fig. 1) at 20 °C and relative humidity of 35%, as it was described in more details elsewhere [16,18].…”

Section: Methodsmentioning

confidence: 99%

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Study of nanoporous in humidity-sensitive MgAl2O4 ceramics with positron annihilation lifetime spectroscopy

Klym¹

2011

Semicond. Phys. Quantum Electron. Optoelectron.

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Abstract. It has been shown that positron annihilation lifetime spectroscopy is a quite promising tool for nanostructural characterization of humidity-sensitive spinel-type MgAl 2 O 4 ceramics. The results have been achieved using the four-component fitting procedure with arbitrary lifetimes that is applied to mathematically treat the measured spectra. It has been shown that the Tao-Eldrup model is adequate to calculate the nanopore size in MgAl 2 O 4 ceramics if using the lifetime values of the third and fourth components.

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“…Figure 1 shows the second lifetime τ 2 and its relative intensity I 2 of PM-355 samples as a function of gamma dose. The middle positron lifetime τ 2 can be connected with positron annihilation on structurally intrinsic free volume traps, such as extended vacancy-like clusters [31]. The unirradiated sample had a τ 2 of about 402 ps, so the vacancies in the sample are called vacancy clusters [32].…”

Section: Positron Annihilation Lifetimementioning

confidence: 99%

Microstructural Investigation of PM-355 Nuclear Track Detector Subjected to Low-Dose Gamma Irradiation: A Positron Annihilation Lifetime Study

Hassan¹

2013

MSA

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Samples of the PM-355 polymeric solid state nuclear track detector were exposed to low gamma absorbed doses from 1 kGy (0.1 Mrad) up to 9 kGy (0.9 Mrad). Positron annihilation lifetime (PAL) in conjunction with transmission electron microscopy (TEM) and Thermo-gravimetric analysis (TGA) were performed on irradiated and pristine samples at room temperature. The observed lifetime spectra were resolved into three components where the ortho-positronium (o-Ps) lifetime component was associated with the pick-off annihilation of positronium trapped by the free volume. PAL studies of irradiated PM-355 samples showed that ortho-positronium (o-Ps) lifetime increases with an increase in dose up to 4 kGy and decreases at higher doses. In contrast, the intensity of the o-Ps component, I 3 , decreases with the dose up to about 2 kGy, followed by a much smooth decrease up to 7 kGy, and then it levels off. TGA analysis indicated that the PM-355 detector decomposed in one main breakdown stage. These results are discussed on the basis of chemical and physical changes occurring at the microscopic level in the PM-355 due to irradiation. Crosslinking dominates for doses between 1 and 4 kGy, while the degradation mechanism (Chain scission) prevails for doses up to 9 kGy.

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PAL spectroscopy in application to humidity-sensitive MgAl2O4 ceramics

Cited by 38 publications

References 3 publications

Defect characterization methodology in sintered functional spinels with PALS technique

Defect characterization methodology in sintered functional spinels with PALS technique

Study of nanoporous in humidity-sensitive MgAl2O4 ceramics with positron annihilation lifetime spectroscopy

Microstructural Investigation of PM-355 Nuclear Track Detector Subjected to Low-Dose Gamma Irradiation: A Positron Annihilation Lifetime Study

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