It is well known that by the coordinated action of atoms arranged in rows and planes in the crystal lattice, the motion of
charged particles such as protons, alpha particles and heavier ions can be influenced so that their range in the single crystals
is considerably enhanced in low-index directions. A technique has been developed based on such enhanced penetration (channeling)
of radioactive atoms (220Rn) emitted by recoil with a 100 keV energy from a224Ra point source to record channeling patterns which show the crystal structure. The radioactive recoil atoms impinging from
this source on the surface of a single crystal penetrate deeper in places where their direction of impact is identical with
low index crystal directions and planes. These places can be visualized by autoradiography when having first stripped a thin
layer from the surface corresponding to the random range of the atoms. This technique is generally applicable in close packed
crystals and gives information about the crystal structure of very thin surface layers.
Authors:S. De Angelis Curtis, Krystyna Kurdziel, S. Materazzi, and S. Vecchio
The crystal structure of a manganese(II) 1-allylimidazole complex ([Mn(1-AIm)3(NO3)2], where 1-Aim=1-allylimidazole), was characterized by X-ray diffraction (XRD) using SHELX-97. The thermal behaviour of the
complex was investigated by thermogravimetry (TG) coupled with an FTIR unit. The complex showed a multi-step decomposition
related to the release of the ligand molecules, followed by oxidation. The final residue at 1073 K was found to be manganese(II)
oxide. Evolved gas analysis allowed to prove the oxidative decomposition pattern of the examined complex, initially proposed
by the percentage mass loss data. Finally, a kinetic analysis of the oxidative decomposition steps was made using the Kissinger
equation, while the complex nature of the decomposition kinetics was revealed by the isoconversional Ozawa-Flynn-Wall method.
Authors:T. Sato, F. Ambe, K. Endo, M. Katada, and H. Sano
The crystal structures of oxo-centered trineclear cobalt-iron chloroacetate complex [CoIIFe
O(CH2ClCO2)6(H2O)3]·3H2O (1) was compared with that of previously reported trinuclear iron complex [FeIIFe
O(CH2ClCO2)6(H2O)3]·3H2O (2) which has an isomorphous structure to 1. Compound 1 crystallizes in space group P21/n with Z=4 in a unit cell of a=14.826 (4) Å, b=4.536 (8) Å, c=14.000 (4) Å, =100.32 (2)0 and V=2968 (11) Å3. The structure was refined to R=0.75 and Rw=0.82. The coordination geometries of the three iron atoms are observed equivalent in 1 indicating a static disorder of the position among cobalt and iron atoms. Two distinct FeIII doublets observed in Mössbauer spectra of 1 become an indistinguishable broad doublet by dehydration of crystal water. On the other hand, no significant line-broadening is observed after the dehydration in complex 2. The results indicate that the dehydration in 2 induces a local environmental change reordering of an electronic configuration around iron atoms, whereas the remaining disordering is reflected in Mössbauer spectrum after the dehydration in 1.
Authors:Z. Wu, A. Zhang, D. Shen, M. Leland, F. W. Harris, and S. Z. D. Cheng
Three aromatic polyimides based on 3,3′,4,4′-biphenyl-tetracarboxylic dianhydride (BPDA) and three different diamines 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), 2,2′-dimethyl-4, 4′-diaminophenyl (DMB) or 3,3′-dimethylbenzidine (OTOL) have been synthesized. These polyimides are soluble in hotp-chlorophenol,m-cresol or other phenolic solvents. Fibers have been spun from isotropic solutions using a dry-jet wet spinning method. The as-spun fibers generally exhibit low tensile properties, and can be drawn at elevated temperatures (>380° C) up to a draw ratio of 10 times. Remarkable increases in tensile strength and modulus are achieved after drawing and annealing. The crystal structures of highly drawn fibers were determinedvia wide angle X-ray diffraction (WAXD). The crystal unit cell lattices have been determined to be monoclinic for BPDA-PFMB and triclinic for both BPDA-DMB and BPDA-OTOL. Thermomechanical analysis (TMA) was used to measure thermal shrinkage stress and strain. A selfelongation has been found in the temperature region around 450°C. This phenomenon can be explained as resulting from the structural development in the fibers as evidencedvia WAXD observations.
Authors:S. Aoyagi, Y. Kuroiwa, A. Sawada, H. Kawaji, and T. Atake
Summary The size effect on the crystal structure including the chemical bonding nature has been investigated for several kinds of BaTiO3 nanopowder with the particle sizes down to 50 nm in diameter, by means of powder diffraction using high-energy synchrotron radiation. The Rietveld refinement reveals that the BaTiO3 nanopowder consists of tetragonal and cubic structure components at 300 K. The feature of coexistence can be illustrated by the core/shell model for the particle, in which the shell with a cubic structure covers the core with a tetragonal structure. The thickness of the cubic shell is almost constant irrespective of the particle sizes, and is estimated as approximately 8 nm. Hence, the critical particle-size, where the entire particle is covered with the cubic shell, is suggested as 16 nm. The charge density distributions of the BaTiO3 nanopowder in the cubic phase at 410 K are revealed by the maximum entropy method. Changes in the bonding electron density and the ionic valence expected are not observed clearly even in the 50 nm crystal compared with the bulk crystal.
The phase behavior of semicrystalline, aliphatic nylons is analyzed on the basis of differential scanning calorimetry, DSC,
and quasi-isothermal, temperature-modulated DSC, TMDSC. The data of main interest are the apparent heat capacities, Cp, in the temperature range from below the glass transitions to above the isotropization. Based on the contributions of the
vibrational motion to Cp, as is available from measurements in our laboratory, the ATHAS Data Bank, and multifaceted new TMDSC results, as well as
on information on the crystal structures, NMR, molecular dynamics simulation of paraffin crystals, and quasi-elastic neutron
scattering, the following observations are made: (a) In semicrystalline nylons the glass transition of the mobile-amorphous
phase is broadened to higher temperature. The additionally present rigid-amorphous phase, RAF, undergoes a separate, broad
glass transition at somewhat higher temperature. (b) The transition of the RAF, in turn, overlaps usually with an increase
in large-amplitude motion of the CH2-groups within the crystals and latent heat effects due to melting, recrystallization, and crystal annealing. (c) Above the
glass transitions of the two non-crystalline phases, Cp of the crystals approaches and exceeds that of the melt. This effect is due to additional entropy contributions (disordering)
within the crystals, which may for some nylons lead to a mesophase. In case a mesophase is formed, the Cp drops to the level of the melt as is common for mesophases. (d) Some locally reversible melting is present on the crystal
surfaces, but seems to be minimal for the mesophase. (e) The increasing amount of large-amplitude motion in the crystals is
described as a third glass transition, occurring over a broad temperature range below the melting or disordering transition
from crystal to mesophase.
The assumption of a separate glass transition in ordered phases was previously discovered on analyzing aliphatic poly(oxide)s
such as poly(oxyethylene), POE, and in the broad class of mesophase-forming small and large molecules. To attain a full description
of the globally-metastable, semicrystalline phase-structure of nylons and to understand its properties, one needs quantitative
information about the glass transitions of the two non-crystalline phases and that of the crystal, as well as the various
irreversible and locally reversible order/disorder transitions and their kinetics. Finally, with different substitutions in
the α-position of the backbone structure of nylon 2, one describes poly(amino acid)s which on proper copolymerization yield
proteins. This links the present study to the earlier thermal analyses of all naturally occurring poly(amino acid)s, a number
of copoly(amino acid)s, and globular proteins in their dehydrated states. It will be of importance to check by quantitative
thermal analysis if similar glass transitions and phase structures as seen in the aliphatic nylons are also present in the
poly(amino acid)s to possibly gain new information about the nanophase structure of proteins.
Authors:Diego M. Gil, M. Carolina Navarro, M. Cristina Lagarrigue, J. Guimpel, Raúl E. Carbonio, and M. Inés Gómez
decomposition of Y[Fe(CN) 6 ]·4H 2 O and its structural characterization. We refine the crystalstructure of YFeO 3 using conventional X-ray powder diffraction (PXRD) by Rietveld Analysis. We also follow the decomposition process through IR spectroscopy
Authors:Tea Mihelj, Zoran Štefanić, and Vlasta Tomašić
coordinates as a monodentate ligand and the crystalstructure consists of molecules of an anion and cation connected by hydrogen bonds [ 3 , 4 ]. Possible simultaneous interactions with o -nitro and p -nitro oxygens may lead to the formation of multidentate
Authors:Barbara Barszcz, Joanna Masternak, Maciej Hodorowicz, and Agnieszka Jabłońska-Wawrzycka
this study, we report here the synthesis, spectroscopic analysis, X-ray crystallography and thermal behavior of cadmium(II) complex with 3-hydroxy-2-quinoxalinecarboxylate (L 1 ). We have not found the crystalstructure of [Cd(L 1 ) 2 (H 2 O) 2 ](H 2 O
Authors:R. Umamaheswari, S. Nirmala, P. Sagayaraj, and A. Joseph Arul Pragasam
-prolinium picrate [ 9 ] have been reported. Crystalstructure analysis of l -proline thiourea monohydrate (LPTU) grown by slow evaporation technique at room temperature is reported in this article. Second harmonic generation (SHG) test and the thermal