Infrared studies of spinels—III

Preudhomme, J.; Tarte, P.

doi:10.1016/0584-8539(71)80235-0

Cited by 353 publications

(85 citation statements)

References 9 publications

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“…Based on their results, we added two more oscillators to the short-and the long-wavelength edges of the broad 19 μm band to fit the shoulder at 17 μm and the decrement toward longer wavelengths correctly. These extra oscillators have already been found in previous studies (Fabian et al 2001;O'Horo et al 1972;Preudhomme & Tarte 1971) and might be due to the ratio of Mg/Al-cation disorder and defects, respectively.…”

Section: Crystalline Mgal 2 O 4 (Spinel)mentioning

confidence: 70%

Optical constants of refractory oxides at high temperatures

Zeidler

Posch

Mutschke

2013

A&A

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Context. Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300 K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars. Aims. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points. Methods. A high-temperature, high-pressure cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum (α-Al 2 O 3 ), spinel (MgAl 2 O 4 ), and α-quartz (SiO 2 ), temperature-dependent optical constants were measured from 300 K up to more than 900 K. Small particle spectra were also calculated from these data. Results. All three examined oxides show a significant temperature dependence of their mid-IR bands. For the case of corundum, we find that the 13 μm emission feature -seen in the IR spectra of many AGB stars -can very well be assigned to this mineral species. The best fit of the feature is achieved with oblate corundum grains at (mean) temperatures around 550 K. Spinel remains a viable carrier of the 13 μ feature as well, but only for T < 300 K and nearly spherical grain shapes. Under such circumstances, spinel grains may also account for the 31.8 μm band that is frequently seen in sources of the 13 μm feature and which has not yet been identified with certainty.

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Section: Crystalline Mgal 2 O 4 (Spinel)mentioning

confidence: 70%

Optical constants of refractory oxides at high temperatures

Zeidler

Posch

Mutschke

2013

A&A

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“…Comparing these band positions with spectra of α-Al 2 O 3 and of MgO, one might be tempted to assume that mode A is due to an Al-O vibration, while mode B would originate from an Mg-O vibration. But this is not the case, as Preudhomme & Tarte (1971) have shown in a careful investigation. They demonstrated that both of the above mentioned resonances mainly originate from vibrations of the trivalent, octahedral cation in the spinel lattice, i.e.…”

Section: The Reflectance Spectra and Their Meaningmentioning

confidence: 78%

“…3, at the short-wavelength edge of mode B; and one, called "D", far beyond mode B, at 33 µm. According to Preudhomme & Tarte (1971), mode D must be assigned to an Mg-O vibration, whereas mode C is of a more complex origin.…”

Section: The Reflectance Spectra and Their Meaningmentioning

confidence: 99%

Infrared optical properties of spinels

Fabian¹,

Posch²,

Mutschke³

et al. 2001

A&A

108

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Abstract. In a previous paper, we have proposed magnesium aluminium spinel to be the carrier of the 13 and 17 µm band features observed in the ISO spectra of some red giants. The IR optical properties of spinel strongly depend on its chemistry and its internal structure. To study the dependence of spinel's IR-spectra on its aluminium content, we have synthesized a number of crystals with different Al/Mg-ratios. Additionally, we performed an annealing experiment to investigate the phase transition between ordered and partially disordered spinel taking place at about 1200 K. We derived sets of optical constants of our natural, annealed and synthetic spinels in order to calculate the absorption efficiencies of small (sub-µm-sized) spherical particles. Thereby, it turned out that natural as well as near-stoichiometric synthetic spinel can indeed be considered as a suitable candidate for the carrier of the 13 µm feature observed in the spectra of some oxygen rich circumstellar shells. To illustrate this, we reinvestigated the mean profile of the residual dust emission in the 12-18 µm wavelength range (i.e., in the so-called trough region between the two silicate bands). The reality of the emission feature at 16.8 µm is confirmed by our new investigation. We demonstrated that it is not an instrumental artifact since it is not present in ISO spectra of K-stars. In the course of our laboratory work, we found a third prominent emissivity maximum of spinel at 32 µm. This feature could also be detected in the spectra of the brightest 13 µm band emission sources; we derived its mean band profile, too. The new sets of optical constants here presented have been made available for public access in the electronic database http://www.astro.uni-jena.de.

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“…The origin of the T 1u modes has been the subject of controversy as two possible interpretations were proposed: In one case the two high-frequency phonon modes are related to the displacement of the Cr-X bond in the CrX 6 octahedra, while the two low-frequency phonon modes to the tetrahedra. 16,36,37 It has been shown experimentally [38][39][40] that the materials having an octahedral sublattice as one of the structural units exhibit phonon modes belonging to octahedral vibrations at higher-frequencies compared to the other lattice vibrations.…”

Section: Discussionmentioning

confidence: 99%

Evolution of the optical properties of chromium spinels CdCr2O4, HgCr2S
Rabia
¹
,
Baldassarre
²
,
Tsurkan
³

et al. 2014
Phys. Rev. B
10
2
4
0
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We report pressure-dependent reflection and transmission measurements on ZnCr2Se4, HgCr2S4, and CdCr2O4 single crystals at room temperature over a broad spectral range 200-24000 cm −1 . The pressure dependence of the phonon modes and the high-frequency electronic excitations indicates that all three compounds undergo a pressure-induced structural phase transition with the critical pressure 15 GPa, 12 GPa, and 10 GPa for CdCr2O4, HgCr2S4, and ZnCr2Se4, respectively. The eigenfrequencies of the electronic transitions are very close to the expected values for chromium crystal-field transitions. In the case of the chalcogenides pressure induces a red shift of the electronic excitation which indicates a strong hybridization of the Cr d-bands with the chalcogenide bands.

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Infrared studies of spinels—III

Cited by 353 publications

References 9 publications

Optical constants of refractory oxides at high temperatures

Optical constants of refractory oxides at high temperatures

Infrared optical properties of spinels

Evolution of the optical properties of chromium spinels CdCr2O4, HgCr2S
Rabia
¹
,
Baldassarre
²
,
Tsurkan
³

et al. 2014
Phys. Rev. B
10
2
4
0
View full text Add to dashboard Cite

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Infrared studies of spinels—III

Cited by 353 publications

References 9 publications

Optical constants of refractory oxides at high temperatures

Optical constants of refractory oxides at high temperatures

Infrared optical properties of spinels

Evolution of the optical properties of chromium spinels CdCr2O4, HgCr2SRabia1, Baldassarre2, Tsurkan3 et al. 2014Phys. Rev. B10240View full textAdd to dashboardCite

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Evolution of the optical properties of chromium spinels CdCr2O4, HgCr2S
Rabia
¹
,
Baldassarre
²
,
Tsurkan
³

et al. 2014
Phys. Rev. B
10
2
4
0
View full text Add to dashboard Cite