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ABSTRACT: The decomposition of the cubic perovskite-type oxide Ba(x)Sr(1-x)Co(0.8)Fe(0.2)O(3-delta) (BSCF) into hexagonal and cubic perovskite-type phases has been examined by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) and X-Ray Diffraction (XRD). SEM and TEM measurements reveal that the new hexagonal phase grows predominantly at the grain boundaries of BSCF ceramics and that the cation composition of the newly formed hexagonal phase differs from that of the starting material. An orientational relationship between the hexagonal and the parent cubic phase was also observed. By means of ex situ XRD the phase fraction of the hexagonal phase was determined as a function of annealing time. A kinetic analysis of the data, based on Avrami-type kinetics, indicates that the decomposition is independent of the initial A-site composition, and the obtained reaction order supports the conclusion that the hexagonal phase grows at the grain boundaries in dense ceramic samples.
Physical Chemistry Chemical Physics 09/2010; 12(35):10320-8. · 3.57 Impact Factor
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Georg Schlieper,
Anke Aretz,
Steven C Verberckmoes,
Thilo Krüger,
Geert J Behets,
Reza Ghadimi, Thomas E Weirich,
Dorothea Rohrmann,
Stephan Langer,
Jan H Tordoir,
Kerstin Amann,
Ralf Westenfeld,
Vincent M Brandenburg,
Patrick C D'Haese,
Joachim Mayer,
Markus Ketteler,
Marc D McKee,
Jürgen Floege
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ABSTRACT: Accelerated intimal and medial calcification and sclerosis accompany the increased cardiovascular mortality of dialysis patients, but the pathomechanisms initiating microcalcifications of the media are largely unknown. In this study, we systematically investigated the ultrastructural properties of medial calcifications from patients with uremia. We collected iliac artery segments from 30 dialysis patients before kidney transplantation and studied them by radiography, microcomputed tomography, light microscopy, and transmission electron microscopy including electron energy loss spectrometry, energy dispersive spectroscopy, and electron diffraction. In addition, we performed synchrotron x-ray analyses and immunogold labeling to detect inhibitors of calcification. Von Kossa staining revealed calcification of 53% of the arteries. The diameter of these microcalcifications ranged from 20 to 500 nm, with a core-shell structure consisting of up to three layers (subshells). Many of the calcifications consisted of 2- to 10-nm nanocrystals and showed a hydroxyapatite and whitlockite crystalline structure and mineral phase. Immunogold labeling of calcification foci revealed the calcification inhibitors fetuin-A, osteopontin, and matrix gla protein. These observations suggest that uremic microcalcifications originate from nanocrystals, are chemically diverse, and intimately associate with proteinaceous inhibitors of calcification. Furthermore, considering the core-shell structure of the calcifications, apoptotic bodies or matrix vesicles may serve as a calcification nidus.
Journal of the American Society of Nephrology 03/2010; 21(4):689-96. · 9.66 Impact Factor
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Georg Schlieper,
Dirk Grotemeyer,
Anke Aretz,
Leon J Schurgers,
Thilo Krüger,
Hermann Rehbein, Thomas E Weirich,
Ralf Westenfeld,
Vincent M Brandenburg,
Frank Eitner,
Joachim Mayer,
Jürgen Floege,
Wilhelm Sandmann,
Markus Ketteler
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ABSTRACT: Coral reef aorta is a rare vascular disease with intraluminal calcifications of the dorsal part of the visceral aorta. The pathogenesis of this disease with its topographic and morphologic characteristics is unknown. The aim of our study was to investigate calcification inhibitors and the ultrastructure of calcifications in patients with coral reef aorta.
Ten patients with coral reef aorta were examined. Calcified specimens were investigated by immunohistochemical techniques for the expression of the calcification inhibitors matrix gla protein (MGP) and fetuin-A. Vessel walls were also assessed by electron microscopic techniques including electron energy-lost spectroscopy, electron dispersive spectroscopy, and electron diffraction. Sera of patients were analyzed for fetuin-A, uncarboxylated MGP (ucMGP), and osteoprotegerin.
As assessed by immunohistochemistry, most MGP was detected in the vicinity of calcified regions. Serum levels of the calcification inhibitors ucMGP, fetuin-A, and osteoprotegerin were 370+/-107 nmol/L, 0.57+/-0.03 g/L, and 5.64+/-0.79 pmol/L, respectively. Ultrastructural analysis of calcified specimens showed a core-shell structure with multiple calcification nuclei. Calcifications displayed a fine-crystalline character, and elemental analysis revealed hydroxyl apatite as the chemical compound.
The coral reef aorta represents an extreme exophytic growth of vascular calcification with multiple nuclei which resemble typical media calcification. Positive vascular immunostaining and low serum levels of both fetuin-A and ucMGP suggest a pathophysiologic role of these calcification inhibitors in the development of coral reef aorta.
Annals of Vascular Surgery 02/2010; 24(3):408-14. · 1.03 Impact Factor
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Georg Schlieper,
Dirk Grotemeyer,
Anke Aretz,
Leon J. Schurgers,
Thilo Krüger,
Hermann Rehbein, Thomas E. Weirich,
Ralf Westenfeld,
Vincent M. Brandenburg,
Frank Eitner,
Joachim Mayer,
Jürgen Floege
Annales De Chirurgie Vasculaire. 01/2010; 24(3):446-453.
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ABSTRACT: One key requirement for the production of multinary oxide films by chemical vapor deposition (CVD) or nanocrystalline multinary oxides particles by chemical vapor synthesis (CVS) is the availability of precursors with high vapor pressure. This is especially the case for CVS where much higher production rates are required compared to thin films prepared by CVD. However, elements, which form low valent cations such as alkaline earth metals, are typically only available as solid precursors of low volatility, e.g., in form of beta-diketonates. This study describes laser flash evaporation as precursor delivery method for CVS of nanocrystalline perovskites. Laser flash evaporation exploits the nonequilibrium evaporation of solid metal organic precursors of low vapor pressure by absorption of the infrared radiation of a CO(2) laser. It is shown that stoichiometric, nanocrystalline particles consisting of SrZrO(3) and SrTiO(3) can be formed from corresponding mixtures of beta-diketonates which are evaporated nonselectively and with high rates by laser flash evaporation.
Review of Scientific Instruments 01/2008; 78(12):123903. · 1.37 Impact Factor
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ABSTRACT: The present work deals with the ab initio determination of the heavy metal framework in Cs(x)(Nb, W)(5)O(14) from precession electron diffraction intensities. The target structure was first discovered by Lundberg and Sundberg [Ultramicroscopy 52 (1993) 429-435], who succeeded in deriving a tentative structural model from high-resolution electron microsopy (HREM) images. The metal framework of the compound was solved in this investigation via direct methods from hk0 precession electron diffraction intensities recorded with a Philips EM400 at 100 kV. A subsequent (kinematical) least-squares refinement with electron intensities yielded slightly improved co-ordinates for the 11 heavy atoms in the structure. Chemical analysis of several crystallites by EDX is in agreement with the formula Cs(0.44)Nb(2.54)W(2.46)O(14). Moreover, the structure was independently determined by Rietveld refinement from X-ray powder data obtained from a multi-phasic sample. The compound crystallises in the orthorhombic space group Pbam with refined lattice parameters a=27.145(2), b=21.603(2), and c=3.9463(3)A. Comparison of the framework structure from electron diffraction with the result from Rietveld refinement shows an average agreement for the heavy atoms within 0.09 A.
Ultramicroscopy 03/2006; 106(3):164-75. · 2.47 Impact Factor
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Thomas E Weirich
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ABSTRACT: The crystal structures of Ti(11)Se(4) [Weirich, Ramlau, Simon, Hovmöller & Zou (1996). Nature (London), 382, 144-146] and Ti(45)Se(16) [Weirich (2001). Acta Cryst. A57, 183-191] determined previously from selected-area electron diffraction (SAED) data have been checked for their correctness by means of total energy calculations within the non-local density functional theory. The reliability of the used method was verified by test calculations carried out for the structurally related compound Ti(8)Se(3), which is well known from single-crystal X-ray diffraction [Weirich, Pöttgen & Simon (1996). Z. Kristallogr. 212, 929-930]. For Ti(8)Se(3), structural models from both experiment and calculation show a perfect match (average agreement 0.01 A). This proves that the geometrical optimized models from first-principles calculation can be used as a reliable alternative when good-quality X-ray results cannot be obtained. Calculations carried out for the two structures determined from electron crystallography yielded average improvement of the atomic coordinates of 0.04 and 0.09 A for Ti(11)Se(4) and Ti(45)Se(16), respectively. The optimized cell parameters of the monoclinic structures (both space group C2/m, No. 12) are a = 25.51, b = 3.43, c = 19.19 A, beta = 117.9 degrees for Ti(11)Se(4) and a = 36.31, b = 3.45, c = 16.59 A, beta = 92.1 degrees for Ti(45)Se(16). These results prove that crystals that are too small for single-crystal X-ray diffraction and are difficult to solve by powder diffraction may nevertheless be amenable to accurate structure determination by electron diffraction structure analysis using data from standard SAED and the assumption of quasi-kinematical scattering. Moreover, this study shows that geometry optimization by first-principles calculations is the perfect tool for validation and improvement of complex structural models, which are suspected to have errors owing to the poor quality of experimental data.
Acta Crystallographica Section A Foundations of Crystallography 02/2004; 60(Pt 1):75-81. · 2.08 Impact Factor
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ABSTRACT: Series of sputter-deposited Co25Ag75 and (Co90Al10)28Ag72 giant-magnetoresistance granular films were characterized by electron diffraction, high-resolution transmission electron microscopy and electron spectroscopic imaging. Crystalline particles of fcc silver and hcp cobalt were detected in both thin-film systems before annealing. Annealing of (Co90Al10)28Ag72 films at 773 and 823 K yielded mixtures of fcc and hcp cobalt clusters and notably enlarged silver particles. In addition, crystallites of bcc Ag3Al were detected in the sample annealed at 823 K. The mesoscopic structure of the as-deposited films was investigated by dark-field imaging showing columnar growth-domains for silver. The columns were preserved during thermal treatment up to 773 K, whereas annealing at 823 K destroyed these domains.
Journal of Electron Microscopy 02/2003; 52(2):91-100. · 1.31 Impact Factor
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ABSTRACT: The alpha structure as well as the new beta modification of Ti(2)Se were recently characterized by electron diffraction structural analysis of nanosize crystallites. In this study, both structures are investigated by means of total energy calculations within the non-local density-functional theory in order to validate the experimental results. The calculated parameters for both modifications are in excellent agreement with data determined from electron microscopy. From the calculated equation of states, beta-Ti(2)Se is predicted to be a high-pressure modification. The present investigation proves by a well established non-crystallographic method that unknown structures, which are not accessible by other standard crystallographic techniques, can be solved and refined with high accuracy using electron diffraction data.
Acta Crystallographica Section A Foundations of Crystallography 02/2003; 59(Pt 1):18-21. · 2.08 Impact Factor
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ABSTRACT: X-ray specular-reflectivity measurements have been carried out on Ag75Co25 granular films which were sputter-deposited on Si substrates with SiO2 surface, to investigate the evolution of surface roughness as a function of film thickness. X-ray reflectivity data were recorded for thicknesses of Ag75Co25 thin films ranging from 8.8-116.9 nm. A power law behaviour of the interfacial width of a growing interface in sputtered-deposited Ag75Co25 granular films was observed. The scaling exponent was found to be β = 0.43±0.01 and compared with theoretical calculations. High resolution electron microscopy revealed the presence of crystalline particles of fcc Ag and hcp Co. The structural and magnetoresistive properties of the films are discussed.
Journal of Physics Condensed Matter 10/2000; 12(44):9237. · 2.55 Impact Factor
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ABSTRACT: The present work deals with the ab initio determination of the heavy metal framework in Csx(Nb, W)5O14 from precession electron diffraction intensities. The target structure was first discovered by Lundberg and Sundberg [Ultramicroscopy 52 (1993) 429–435], who succeeded in deriving a tentative structural model from high-resolution electron microsopy (HREM) images. The metal framework of the compound was solved in this investigation via direct methods from h k 0 precession electron diffraction intensities recorded with a Philips EM400 at 100 kV. A subsequent (kinematical) least-squares refinement with electron intensities yielded slightly improved co-ordinates for the 11 heavy atoms in the structure. Chemical analysis of several crystallites by EDX is in agreement with the formula Cs0.44Nb2.54W2.46O14. Moreover, the structure was independently determined by Rietveld refinement from X-ray powder data obtained from a multi-phasic sample. The compound crystallises in the orthorhombic space group Pbam with refined lattice parameters a=27.145(2), b=21.603(2), and . Comparison of the framework structure from electron diffraction with the result from Rietveld refinement shows an average agreement for the heavy atoms within 0.09 Å.
Ultramicroscopy.
