Comparisons of atomic thermal motions for graphite at 300 K based on X-ray, neutron, and phonon-spectrum data

1978 ◽  
Vol 34 (6) ◽  
pp. 979-982 ◽  
Author(s):  
R. Chen ◽  
P. Trucano
Keyword(s):  
Phonon Spectrum ◽  
Mean Square ◽  
Temperature Dependent ◽  
X Ray ◽  
The Core ◽  
Out Of Plane ◽  
Density Analysis ◽  
Atomic Scattering ◽  
The Mean ◽  
Spectrum Model

The mean-square amplitudes of vibration in graphite based on an X-ray charge-density analysis are 0.0032 (2) and 0.0140 (3) Å2 parallel to and perpendicular to the basal plane, respectively. Values for the parallel vibrations of 0.0031 (6) and 0.0032 Å2 were derived from temperature-dependent neutron measurements and a calculated phonon spectrum. The neutron measurements and the phonon spectrum both predict lower values [0.0090 (20) and 0.0098 Å2] for the out-of-plane vibrations. This small discrepancy may be caused by small changes in the core atomic scattering factors from the free-atom values or by a deficiency in the phonon-spectrum model.

A Conformational Study of 5,10,15,20-Tetraalkyl-22H+,24H+-porphyrindiium Salts (Dication Salts)

2000 ◽  
Vol 55 (3-4) ◽  
pp. 336-344 ◽  
Author(s):  
Mathias O. Senge
Keyword(s):  
Free Base ◽  
Conformational Study ◽  
Steric Strain ◽  
X Ray ◽  
Tert Butyl ◽  
The Core ◽  
Out Of Plane ◽  
The Mean ◽  
Porphyrin Core ◽  
Tertiary Alkyl

Abstract N-protonation of 5,10,15,20-tetraalkylporphyrins with n-butyl, isobutyl, isopropyl, 1-ethyl-propyl or tert-butyl substituents yields the respective 22,24-dihydroporphyrins (22H+,24H+-porphyrindiium salts) that exhibit highly nonplanar conformations. Depending on the steric demand of the meso substituents, the free base porphyrins have planar to moderately ruffled macrocycles (primary or secondary alkyl residues) or are severely ruffled (tertiary alkyl resi­dues). X-ray crystallographic studies show that protonation of porphyrins with n-Bu (2), i-Pr (3) or EtPr (4) substituents leads to steric congestion of the core resulting in symmetric, saddle distorted macrocycles as evidenced by average displacements of the Cb positions from the mean plane ranging from 0.79 to 1.01 Å. The structures observed for these porphyrin diacids are very similar in distortion mode and degree of nonplanarity to 5,10,15,20-tetraaryl-22H+,24H+-porphyrindiium salts and to 2,3,7,8,12,13,17,18-octaalkyl-5,10,15,20-tetraaryl-porphyrins. In contrast, protonation of the highly ruffled 5,10,15,20-tetrakis(teA-r-butyl)porph-yrin results in a switch of the conformational distortion mode. The dication 6 shows both saddle distortion (Cb displacements -1.3 Å) and ruffling of the macrocycle (Cm displacements of approx. 0.48 Å). Thus, the need to accomodate four N-H units in the porphyrin core with its associated out-of-plane tilting of the pyrrole rings and the steric strain induced at the meso carbon atoms results in a highly nonplanar porphyrin with mixed distortion modes.

Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 164-165
Author(s):  
Noriyuki Kuwano ◽  
Masaru Itakura ◽  
Kensuke Oki
Keyword(s):  
Electron Microscopy ◽  
Mean Value ◽  
Heavy Elements ◽  
Arc Furnace ◽  
X Ray ◽  
Long Period ◽  
Ultra High Purity ◽  
Heat Treated ◽  
Atomic Scattering ◽  
The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

X-ray structural studies of epitaxial yttrium silicide on Si(111)

1994 ◽  
Vol 9 (6) ◽  
pp. 1434-1440 ◽  
Author(s):  
L.J. Martínez-Miranda ◽  
J.J. Santiago-Avilés ◽  
W.R. Graham ◽  
P.A. Heiney ◽  
M.P. Siegal
Keyword(s):  
Unit Cell Volume ◽  
Film Growth ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Correlation Lengths ◽  
X Ray ◽  
Lattice Constants ◽  
Glancing Angle ◽  
Out Of Plane ◽  
The Mean

We performed a series of glancing angle and reflection x-ray diffraction experiments to study both the in-plane and out-of-plane structure of epitaxial YSi2−x films grown on Si(111), with thicknesses ranging from 85 Å to 510 Å. These measurements allowed us to characterize the mean film lattice constants, the position correlation lengths of the film, and the presence and extent of strain as a function of film thickness. We find that the strain along the basal plane increases as a function of increasing thickness to approximately 1% in the 510 Å film; the corresponding out-of-plane strain is such that the film unit cell volume increases as a function of thickness. The corresponding in-plane microscopic strain varies from 0.5% for the 85 Å film to 0.3% for the 510 Å film. We relate our results to the mode of film growth and the presence of pinholes in the films.

X-ray investigation of the mean square thermal displacements in VDx, NbHx and TaHx interstitial alloys

1983 ◽  
Vol 44 (10) ◽  
pp. 985-989 ◽  
Author(s):  
H. Behr ◽  
H.M. Keppler ◽  
G. Steyrer ◽  
H. Metzger ◽  
J. Peisl
Keyword(s):  
Mean Square ◽  
X Ray ◽  
Thermal Displacements ◽  
The Mean

Variable-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type barium titanate phases

2016 ◽  
Vol 72 (1) ◽  
pp. 151-159 ◽  
Author(s):  
Tomotaka Nakatani ◽  
Akira Yoshiasa ◽  
Akihiko Nakatsuka ◽  
Tatsuya Hiratoko ◽  
Tsutomu Mashimo ◽  
...  
Keyword(s):  
Single Crystal ◽  
Diffraction Study ◽  
Variable Temperature ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray ◽  
M Phase ◽  
The Mean ◽  
Perovskite Type

A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3perovskite has been performed over the temperature range 298–778 K. A transition from a tetragonal (P4mm) to a cubic (Pm \overline 3 m) phase has been revealed near 413 K. In the non-centrosymmetricP4mmsymmetry group, both Ti and O atoms are displaced along thec-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti4+and Ba2+cations occupy off-center positions in the TiO6and BaO12polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.

IMPROVEMENT OF RADIOSENSITIVE LIQUID-CORE MICROCAPSULES BY YTTRIUM POLYMERIZATION

2007 ◽  
Vol 17 (01n02) ◽  
pp. 33-40 ◽  
Author(s):  
S. HARADA ◽  
S. EHARA ◽  
K. ISHII ◽  
H. YAMAZAKI ◽  
S. MATSUYAMA ◽  
...  
Keyword(s):  
Hyaluronic Acid ◽  
Liquid Core ◽  
Acid Solutions ◽  
Alginate Solution ◽  
X Ray ◽  
The Core ◽  
Radiation Induced ◽  
Γ Rays ◽  
The Mean ◽  
Maximum Content

Microcapsules comprising alginate and hyaluronic acid that can be decomposed by radiation are under development. Previously, we observed that radiation efficiently decomposes microcapsules comprising alginate and hyaluronic acid in the ratio 2:1 by weight. In this study, Yttrium ( Y ) was added to these microcapsules to improve their decomposition by radiation. Hyaluronic acid solutions (0.1% weight/volume) were mixed into 0.2% alginate solution, and carboplatin (0.2 mmol) was added; the resultant was used for capsule preparation. Capsules were prepared by spraying the material into mixtures of 4.34% CaCl 2 solution supplemented with Y at final concentrations from 0 to 1.0 × 10−2%. These capsules were irradiated by a single dose of 0.5, 1.0, 1.5, or 2 Gy with 60Co γ-rays. Immediately after irradiation, we observed the release of the core contents of the microcapsule using a micro Particle Induced X-ray Emission (PIXE) camera. The mean diameter of the microcapsules was 37.3 ± 7.8 μm . Maximum content of radiation-induced release was observed for liquid-core microcapsules prepared by polymerization in a 4.34% CaCl 2 solution supplemented with 5.5 × 10−3% Y .

An energy-dispersive X-ray diffraction study of mean-square atom displacements in highly oriented pyrolytic graphite

1986 ◽  
Vol 19 (3) ◽  
pp. 200-201 ◽  
Author(s):  
T. H. Metzger
Keyword(s):  
Pyrolytic Graphite ◽  
Energy Dispersive ◽  
Mean Square ◽  
Highly Oriented Pyrolytic Graphite ◽  
X Ray Diffraction ◽  
Thermal Diffuse Scattering ◽  
X Ray ◽  
Integrated Intensity ◽  
The Mean ◽  
Thermal Diffuse

The measurement of the mean-square thermal displacement 〈u 2〉 of carbon atoms in highly oriented pyrolytic graphite (HOPG) in the hexagonal c direction is reported. Energy-dispersive X-ray diffraction (EDXD) has been used to study the integrated intensity of all Bragg reflections 004 through 0′0′14 as a function of temperature. It is demonstrated that the correction of the Bragg intensities due to thermal diffuse scattering contributions is very important for HOPG, when EDXD is used. The Debye temperature ΘD = 554 (30) K is obtained.

Synthesis, lead lability and ring deformation of three 1,4,8,11,15,18,22,25-octasubstituted phthalocyaninato lead derivatives

2006 ◽  
Vol 10 (10) ◽  
pp. 1202-1211 ◽  
Author(s):  
Paul M. Burnham ◽  
Isabelle Chambrier ◽  
David L. Hughes ◽  
Benjamin Isare ◽  
Richard J. Poynter ◽  
...  
Keyword(s):  
The Other ◽  
Lead Ion ◽  
X Ray Diffraction ◽  
Steric Interactions ◽  
X Ray ◽  
The Core ◽  
Benzene Rings ◽  
Methylene Groups ◽  
The Mean ◽  
Work Up

The syntheses and attempted syntheses of some non-peripherally (1,4,8,11,15,18,22,25) octasubstituted lead phthalocyanines from their corresponding metal-free derivatives are described. Some compounds exhibited lability of the lead ion during work-up to regenerate the starting material. The results of single crystal X-ray diffraction analyses of 1,4,8,11,15,18,22,25-octahexyl-, 1,4,8,11,15,18,22,25-octa-iso-pentyl- and 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanines are reported and cast some light on the greater stability of 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine, in terms of ease of loss of the lead ion, over the other two substituted lead phthalocyanines studied. The phthalocyanine cores of all three derivatives adopt a saddle-shaped geometry rather than the saucer-shaped conformation exhibited by unsubstituted lead phthalocyanine. The saddle-shaped conformation would appear to offer a means of relieving steric interactions between the substituents on adjacent benzene rings. That steric interactions are a feature of these molecules is perhaps reflected in the different distortions of the saddle conformations. This is greatest for compound 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanine bearing the isopentyl groups, expected to introduce the most interactions, and least for compound 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine where S atoms rather than methylene groups are adjacent to the benzene ring. The molecules of 1,4,8,11,15,18,22,25-octahexyl- and 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine pack together in pairs with their nearest neighbouring molecule; their lead atoms, displaced from the core and directed towards each other. The presence of the S atoms in 1,4,8,11,15,18,22,25-octahexylsulfanyl lead phthalocyanine leads to close Pb … S contacts between the molecules. Attractive Pb … S interactions in this compound may also account for the larger displacement of the Pb from the mean-plane of the four coordinated nitrogen atoms at the centre of the phthalocyanine core than is found for 1,4,8,11,15,18,22,25-octahexyl- and 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanines. The molecular packing of 1,4,8,11,15,18,22,25-octa-iso-pentyl lead phthalocyanine is more complex because of the presence of tetrahydrofuran molecules (the solvent of recrystallisation) within the crystal, offering additional interactions with the Pb atoms.

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