Experimental proof of the distinct electronic structure of a new meteoritic Fe–Ni alloy phase

Rancourt, Denis; Lagarec, Ken; Densmore, A.; Dunlap, R. A.; Goldstein, Joseph I.; Reisener, R. J.; Scorzelli, R. B.

doi:10.1016/s0304-8853(98)00366-7

Cited by 39 publications

(36 citation statements)

References 17 publications

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“…Zoned taenite grains also exhibit dark-etching "cloudy zone" interiors which consist of submicron intergrowths of tetrataenite, antitaenite (a low moment phase), and martensite (Figs. 2-6) (Yang et al 1997;Rancourt et al 1999). Taenite grains in H and L chondrites occasionally contain martensite cores (Fig.…”

Section: Metallography Of Zoned Taenite + Kamacite Particlesmentioning

confidence: 99%

Ordinary chondrite metallography: Part 2. Formation of zoned and unzoned metal particles in relatively unshocked H, L, and LL chondrites

Reisener¹,

Goldstein²

2003

Meteorit & Planetary Scien

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Abstract-We studied the metallography of Fe-Ni metal particles in 17 relatively unshocked ordinary chondrites and interpreted their microstructures using the results of P-free, Fe-Ni alloy cooling experiments (described in Reisener and Goldstein 2003). Two types of Fe-Ni metal particles were observed in the chondrites: zoned taenite + kamacite particles and zoneless plessite particles, which lack systematic Ni zoning and consist of tetrataenite in a kamacite matrix. Both types of metal particles formed during metamorphism in a parent body from homogeneous, P-poor taenite grains. The phase transformations during cooling from peak metamorphic temperatures were controlled by the presence or absence of grain boundaries in the taenite particles. Polycrystalline taenite particles transformed to zoned taenite + kamacite particles by kamacite nucleation at taenite/taenite grain boundaries during cooling. Monocrystalline taenite particles transformed to zoneless plessite particles by martensite formation and subsequent martensite decomposition to tetrataenite and kamacite during the same cooling process. The varying proportions of zoned taenite + kamacite particles and zoneless plessite particles in types 4-6 ordinary chondrites can be attributed to the conversion of polycrystalline taenite to monocrystalline taenite during metamorphism. Type 4 chondrites have no zoneless plessite particles because metamorphism was not intense enough to form monocrystalline taenite particles. Type 6 chondrites have larger and more abundant zoneless plessite particles than type 5 chondrites because intense metamorphism in type 6 chondrites generated more monocrystalline taenite particles. The distribution of zoneless plessite particles in ordinary chondrites is entirely consistent with our understanding of Fe-Ni alloy phase transformations during cooling. The distribution cannot be explained by hot accretion-autometamorphism, post-metamorphic brecciation, or shock processing.

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Section: Metallography Of Zoned Taenite + Kamacite Particlesmentioning

confidence: 99%

Ordinary chondrite metallography: Part 2. Formation of zoned and unzoned metal particles in relatively unshocked H, L, and LL chondrites

Reisener¹,

Goldstein²

2003

Meteorit & Planetary Scien

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“…In the study of Fe-Ni-bearing meteorites, there is a recent discussion about the formation of a low-moment Fe-rich γ phase which differs from the ordinary high-spin γ phase in the electronic structure and a lower lattice parameter, but has the same crystal structure, same degree of atomic order and same composition of ordinary taenite. In fact, this has been claimed to be a new mineral called antitaenite which is common in slowly cooled meteorites [12][13][14]. This low-spin phase is proposed to occur in a thin epitaxial intergrowth with tetrataenite (ferromagnetic atomically ordered FeNi).…”

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confidence: 99%

“…Finally, we would like to emphasize that a low-spin iron-rich phase was not detected in this study since our focus of attention was only in bulk samples (in natura). A chemical treatment of the samples is needed in order to eliminate the bcc phase and to obtain the lamelae (plate or needle-shaped crystals, formed during the slow cooling of meteoroids) containing the fcc phases [14] (tetrataenite and anti-taenite) which are expected to be present in all iron bearing meteorites. This can be the subject of a further investigation.…”

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confidence: 99%

A Mössbauer effect study of the Soledade meteorite

Paduani

Pérez²,

Ardisson

2005

Braz. J. Phys.

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We performed a Mössbauer spectroscopy study of the iron meteorite Soledade. This meteorite, which consists of a metallic matrix, is an octahedrite with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. A chemical analysis indicates 6.78 % Ni, 0.46% Co, besides traces of Cu, Cr, Ga, Ge, As, Sb, W, Re, Ir and Au. No traces of silicates have been found and no oxygen was detected. Iron is appearing in the austhenitic phase and alloyed with nickel. An analysis of the Mössbauer spectra at room temperature indicates that the Fe-Ni phase is homogeneously distributed in the matrix, although variations in the composition between different regions are observed.Since the early studies of the microstructure and chemical composition of meteorites the formation of magnetic phases has attracted the attention of metallurgists [1][2][3][4][5][6][7][8][9][10][11]. Most of the metallic specimens presented high contents of nickel and iron as major constituents, and thus the Fe-Ni alloys formed under such special conditions have been the subject of several investigations with a variety of experimental techniques. This is not an easy task considering the weathering process and the distribution of oxides in the metallic matrix, which in some cases varies in composition from one region to another. However, the complexity of the mechanism of formation of the alloys in meteorites, which can take cooling rates as long as 1 K/Ma, is an interesting subject, and its comprehension may shed some light on the metastability of alloys.The category of iron meteorites corresponds to about 5 % of the modern meteorite falls. In the study of Fe-Ni-bearing meteorites, there is a recent discussion about the formation of a low-moment Fe-rich γ phase which differs from the ordinary high-spin γ phase in the electronic structure and a lower lattice parameter, but has the same crystal structure, same degree of atomic order and same composition of ordinary taenite. In fact, this has been claimed to be a new mineral called antitaenite which is common in slowly cooled meteorites [12][13][14]. This low-spin phase is proposed to occur in a thin epitaxial intergrowth with tetrataenite (ferromagnetic atomically ordered FeNi). Actually, metastable precipitates of this low-spin phase in a matrix of high-spin Fe-Ni phase of the same controlled composition have been synthetically produced near the Invar composition (≈ 35 at% Ni).In this work we applied x-ray diffraction (XRD) and Mössbauer spectroscopy (MS) to study the iron-bearing phases detected in the iron meteorite called Soledade, which is a massive metallic block [15]. Although no one knows precisely when this specimen was found, it received the name of the locality from where it proceeded near the city of Passo Fundo in the state of Rio Grande do Sul in Brazil. The first studies indicate that this metallic meteorite is an octahedrite, with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. It consists of a solid block weighing 68 kg, with a...

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“…Comparing configurations A and B, it is seen that the effect of Ni first-neighbours of Fe is to increase μ and the magnitudes of HF. It is concluded that only a smaller lattice constant may explain the low values of IS in these alloys [3,12], as compared to ordered FeNi and FM disordered alloys.…”

Section: Resultsmentioning

confidence: 88%

Theoretical investigation of Mössbauer hyperfine interactions in ordered FeNi and disordered Fe–Ni alloys

Guenzburger

Terra

2006

Hyperfine Interact

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Electronic structure spin-polarized calculations were performed for 79-atoms embedded clusters representing the ordered intermetallic compound FeNi, the fcc Fe-rich disordered alloy Fe 85 Ni 15 in an antiferromagnetic (AFM) configuration, and the ferromagnetic (FM) disordered alloy Fe 50 Ni 50 . The spin-polarized discrete variational method (DVM) in Density Functional theory was employed. Spin magnetic moments, as well as the 57 Fe Mössbauer hyperfine parameters isomer shift and magnetic hyperfine fields, were obtained from the calculations. For FM Fe 50 Ni 50 , the effect of pressure on the hyperfine field and on the isomer shift was investigated, for three different local atomic configurations surrounding the 57 Fe probe atom. In the case of the isomer shift, the calculated values were compared to reported experimental data.

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Experimental proof of the distinct electronic structure of a new meteoritic Fe–Ni alloy phase

Cited by 39 publications

References 17 publications

Ordinary chondrite metallography: Part 2. Formation of zoned and unzoned metal particles in relatively unshocked H, L, and LL chondrites

Ordinary chondrite metallography: Part 2. Formation of zoned and unzoned metal particles in relatively unshocked H, L, and LL chondrites

A Mössbauer effect study of the Soledade meteorite

Theoretical investigation of Mössbauer hyperfine interactions in ordered FeNi and disordered Fe–Ni alloys

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