Ordnung/Unordnung und Ultrarotabsorption IV. Die Absorption einiger Metalloxyde mit Spinellstruktur

Hafner, S. S.

doi:10.1524/zkri.1961.115.5-6.331

Cited by 217 publications

(48 citation statements)

References 11 publications

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“…In ferrites, the metals ions are situated in two different sublattices designated tetrahedral (A-site) and octahedral (B-site) according to the geometrical configuration of the oxygen nearest neighbours. Waldron (1955) and Hafner (1961) have attributed the band around 600 cm -1 to stretching vibrations of the tetrahedral groups (t 1 * ) and that around 400 cm -1 to the octahedral groups (t 2 * ). The IR spectra for the powder in the main form of Li 0.5 Fe 2.5 O 4 as prepared and annealed at different temperatures (600, 800, 1,000 and 1,200°C) were recorded in the range of 200-1,500 cm -1 are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Structural, magnetic and electrical properties of the lithium ferrite obtained by ball milling and heat treatment

Mazen

Abu-Elsaad

2014

Appl Nanosci

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The physical properties of ferrites are very sensitive to microstructure, which in turn critically depends on the manufacturing process. Lithium ferrite is synthesized by milling process. The powder was annealed at four different temperatures 600, 800, 1,000 and 1,200°C. The powder annealed at 600°C has the spinel structure with some of a-Fe 2 O 3 , while the powders annealed at C800°C formed in single-phase cubic spinel structure. Particle size of lithium ferrite is in the range of 26-70 nm, and is dependent on the annealing temperature. The saturation magnetization increased from 22 to 85 emu/g and the coercivity decreases from 124 to 4 Oe with increase in the annealing temperature. The dielectric constant (e'), dielectric loss (tan d) and ac conductivity (r ac ) were measured at room temperature as a function of frequency. The results of dielectric properties were explained in terms of Koops phenomenological theory.

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Section: Resultsmentioning

confidence: 99%

Structural, magnetic and electrical properties of the lithium ferrite obtained by ball milling and heat treatment

Mazen

Abu-Elsaad

2014

Appl Nanosci

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“…Two main broad metal- oxygen bands are seen in the IR spectra of all spinels and ferrites in particular. The highest one, ν 1 , generally observed in the range 600-500 cm −1 , corresponds to intrinsic stretching vibrations of the metal at the tetrahedral site, M tetra ↔ O, whereas the ν 2 -lowest band, usually observed in the range 450-385 cm −1 , is assigned to octahedral-metal stretching, M octa ↔ O [26,27]. The band, observed at around 561 cm −1 for ZnFe 2 O 4 can be assigned to tetrahedral Zn 2+ stretching, ν 1 , and the band observed at 453 cm −1 involves the Fe 3+ vibration at the octahedral site, ν 2 (Fig.…”

Section: Ftir Studiesmentioning

confidence: 98%

Synthesis and characterization of ZnFe2O4 magnetic nanoparticles via a PEG-assisted route

Köseoğlu

Baykal

Toprak

et al. 2008

Journal of Alloys and Compounds

135

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“…Previous studies of crystalline spinel have found peaks at wavelengths longwards of 13.5 µm (e.g. Chopelas & Hofmeister 1991;Hafner 1961;Preudhomme & Tarte 1971). Indeed, it was these previously published spectra which prompted Speck (1998) to ignore spinel in her discussion of mid-IR dust features because it did not appear to have any features in the 7.5 − 13.5 µm window and would therefore not be a candidate for the 13 µm feature.…”

Section: Which Minerals?mentioning

confidence: 99%

Dust features in the 10-μm infrared spectra of oxygen-rich evolved stars

Speck¹,

Barlow

Sylvester

et al. 2000

Astron. Astrophys. Suppl. Ser.

181

226

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Abstract.We have analyzed the 8 − 13.5 µm UKIRT CGS3 spectra of 142 M-type stars including 80 oxygenrich AGB stars and 62 red supergiants, with a view to understanding the differences and similarities between the dust features of these stars. We have classified the spectra into groups according to the observed appearance of the infrared features. In each case the normalized continuumsubtracted spectrum has been compared to those of the other stars to find similarities and form groups. The dust features of the AGB stars are classified into six groups: broad AGB, where the feature extends from 8 µm to about 12.5 µm with little structure; broad+sil AGB, which consists of a broad feature with an emerging 9.7 µm silicate bump; and four silicate AGB groups in which a "classic" 9.7 µm silicate feature gets progressively narrower. Likewise, the supergiant spectra have also been classified into groups, however these do not all coincide with the AGB star groups. In the supergiant case we again have six groups: featureless, where there is little or no emission above the continuum; broad Super, where the feature extends from about 9 µm to about 13 µm; and four silicate Super groups, which again show a progression towards the narrowest "classic" 9.7 µm silicate feature. We compare the mean spectrum for each group, which yields two main results. Firstly, while the "classic" silicate feature is essentially identical for both AGB stars and red supergiants, the broad features observed for these two stellar types are quite different. We suggest that the dust in these two environments follows different evolutionary paths, with the dust around Mira stars, whose broad feature spectra can be fit by a combination of alumina (Al 2 O 3 ) and magnesium silicate, progressing from this composition to dust dominated by magnesium silicate only, while the dust around supergiants, whose broad feature can be fit by a combination of Ca-Al-rich silicate and Al 2 O 3 , progresses Send offprint requests to: A.K. Speck from this initial composition to one eventually also dominated by magnesium silicate. The reason for the difference in the respective broad features is not clear as yet, but could be influenced by lower C/O ratios and chromospheric UV radiation fields in supergiant outflow environments. The second result concerns the 12.5 − 13.0 µm feature discovered in IRAS LRS spectra and widely attributed to Al 2 O 3 . This feature is seen predominantly in the spectra of semiregular variables, sometime in Miras and only once (so far) in supergiant spectra. We argue that it is unlikely that this feature is due to Al 2 O 3 or, as has more recently been suggested, spinel (MgAl 2 O 4 ), but could be associated with silicon dioxide or highly polymerized silicates (not pyroxenes or olivines).

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Ordnung/Unordnung und Ultrarotabsorption IV. Die Absorption einiger Metalloxyde mit Spinellstruktur

Cited by 217 publications

References 11 publications

Structural, magnetic and electrical properties of the lithium ferrite obtained by ball milling and heat treatment

Structural, magnetic and electrical properties of the lithium ferrite obtained by ball milling and heat treatment

Synthesis and characterization of ZnFe2O4 magnetic nanoparticles via a PEG-assisted route

Dust features in the 10-μm infrared spectra of oxygen-rich evolved stars

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