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Magnetic and structural properties of Sc(Fe1−xSix)2Laves phases studied by Mössbauer spectroscopy and neutron diffraction

100%

Wiertel M. , Surowiec Z. , Budzyński M. , Sarzyński J. , Beskrovnyi A. I.

Nukleonika

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2015

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tom 60

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nr 1

155-160

EN

The aim of the presented paper is to study an influence of replacement of Fe atoms by Si atoms in quasibinary Sc(Fe1−xSix)2 Laves phases on their structural and magnetic properties. Powder X-ray diffraction (XRD) and neutron diffraction (ND) measurements carried out at different temperatures from 4.3 K up to about 700 K revealed that samples were single phase with cubic C15 structure for Si concentration x from 0.05 to 0.20 and hexagonal C14 structure for higher concentration. The results of 57Fe Mössbauer measurements showed that the Sc(Fe1−xSix)2 compounds with x ≤ 0.30 are ferrimagnetic at 4.3 K. At temperature 80 K in the samples with x = 0.20 and 0.30, a magnetic cluster spin-glass state has been observed, as ferrimagnetic long-range order disappears. Such picture was supported by the results of ND measurements carried out at 8 K, which confirmed the lack of long-range order for x above 0.10 and an occurrence of hyperfine field distributions in the corresponding Mössbauer spectra. At room temperature, samples with x ≥ 0.20 became paramagnetic. A substitution of Si atoms for Fe ones leads to a decreasing of mean values of hyperfine magnetic fields in samples under investigation. From the neutron diffraction pattern analysis of Sc(Fe0.90Si0.10)2Fe magnetic moment was determined as to be equal to 1.5 μB at 8 K. Combining this result with a value of hyperfine magnetic field on 57Fe probes, the hyperfine coupling constant A in Sc(Fe0.90Cu0.10)2 phases is estimated at about 11.6 T/μB at 8 K.

2

DFT and neutron diffraction study of 1,6-anhydro-β-D-glucopyranose (levoglucosan)

75%

Sládkovic̆ová M. , Mach P. , Smrc̆ok L. u. , Rundlöf H.

Open Chemistry

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2007

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tom 5

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nr 1

55-70

EN

Geometries of 27 generated conformers of levoglucosan were optimized in vacuo at DFT level of theory combining several functionals with high quality basis sets. For the sake of comparison a reference molecular and crystal geometry obtained from 30 K single crystal neutron diffraction data was used. Analysis of the conformers’ geometries revealed that in all stable conformers intramolecular two-or three centre hydrogen bonds were formed. Relative energy of the conformer, which approximated the molecule in the crystal structure the most, was only ∼3 kcal/mol higher, than the energy of the most stable conformer in vacuo. The largest discrepancies between the geometries calculated in vacuo and experimental geometry concentrated in the vicinity of anomeric C1. These differences were reduced by involving O1 to intermolecular hydrogen bond using a simple model of the respective hydrogen bond in the crystal. [...]

3

Diffraction study of thermal dissociation of Ti3AlC2 in vacuum

63%

Pang W. K. , Low I. M.

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2010

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tom T. 62, nr 3

272-274

EN

Titanium aluminum carbide exhibits a unique combination of characteristics of both metals and ceramics coupled with an unusual combination of mechanical, electrical and thermal properties. In this paper, the effect of high-vacuum annealing on the phase stability and phase transition of Ti3AlC2 at up to 1550°C was studied using in-situ neutron diffraction. The decomposition of Ti3AlC2 into TiC was observed from the change of relative phase abundances as a function of temperature. The apparent activation energies of phase decomposition was determined to be -71.9 kJ/mol. Near-surface composition depth profiling using grazing-incidence synchrotron radiation diffraction has revealed a graded phase composition in vacuum-decomposed surfaces.

PL

Węglik tytanowo-glinowy wykazuje unikalną kombinację cech metalicznych i ceramicznych sprzężonych z niezwykłą kombinacją właściwości mechanicznych, elektrycznych i cieplnych. W niniejszym artykule zbadano za pomocą dyfrakcji neutronów, zachodzącej in-situ, wpływ wygrzewania do 1550°C w wysokiej próżni na skład fazowy i przejście fazowe Ti3AlC2. Rozkład Ti3AlC2 do TiC zaobserwowano na podstawie zmiany liczebności faz w funkcji temperatury. Pozorne energie aktywacji procesu rozkładu fazowego określono na -71.9 kJ/mol. Wyznaczenie głębokościowego profilu składu przypowierzchniowego za pomocą dyfrakcji promieniowania synchrotronowego padającego pod małym kątem (GISRD) ujawniło zmieniający się stopniowo skład fazowy w próbkach rozkładanych próżniowo.

4

Single-crystal neutron study on cobalt iodate tetrahydrate, a compound with H...|I(V)O3- hydrogen bonds?

51%

Nagel R. , Kümmerle E. , Lutz H. D.

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2002

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tom Vol. 50, No. 1

51-66

EN

The crystal structure of cobalt iodate tetrahydrate Co(IO(3)(2)-4H(2)O (space group P21/c, Z=2, a=836.8(5) pm, b=656.2(3) pm, c=850.2(5) pm, and Beta=100.12°, final Rl = 0.0349 (I>i mniejszości 2 sigma(I) for 1031 unique reflections) was redetermined by single-crystal neutron diffraction studies. The structure is built up by layers parallel (100) connected by interionic O(3)I(-..'OIO(-)(2) bonds. Unequivocal interpretation of the four differently strong OH(...) OIO(-3) hydrogen bonds of the two crystallographic different hydrate H(2)O molecules of the isostructural series M(IO3)(2)-4H(2)O (M = Mg, Co, Ni) on the basis of the observed hydrogen-bond distances and assignment to the uncoupled OD stretching modes of matrix isolated HDO molecules is only possible if weak hydrogen bonds to the iodine lone-pairs of adjacent IO-(3) ions are additionally considered. The potential strength of H(...)I(V)O-(3) hydrogen bonds with respect to H(...) I distances and H(...)IO(-)(3) angles is discussed. A bond-valence concept for estimating the strength of H(...I)I(V)O(-)(3) hydrogen bonds is given.