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Aerosol Synthesis of Fullerene Nanocrystals in Controlled Flow Reactor Conditions (2000)

Joutsensaari, J. ; Ahonen, P.P. ; Kauppinen, E.I. ; [et al.]

Springer

Journal of nanoparticle research 2 (2000), S. 53-74

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ISSN: 1572-896X

Keywords: aerosol processing ; C60 ; computational fluid dynamics ; fullerene ; lamellar twinned particles ; nanostructured materials

Source: Springer Online Journal Archives 1860-2000

Topics: Physics , Technology

Notes: Abstract Fullerene nanocrystals in the size range 30–300 nm were produced starting from atomized droplets of C60 in toluene. The experiments were carried out under well-controlled conditions in a laminar flow reactor at temperatures of 20–600°C. Particle transformation and crystallization mechanisms of polydisperse and monodisperse (size classified) fullerene aerosol particles were studied. The results show that fullerene particles are roughly spherical having pores and voids at temperatures of 300°C and below. Particles are already crystalline and likely fine-grained at 20°C and they are polycrystalline at temperatures up to 300°C. At 400°C monodisperse particles evaporate almost completely due to their low mass concentration. Polydisperse particles are crystalline, but sometimes heavily faulted. At 500°C most of the particles are clearly faceted. In certain conditions, almost all particles are hexagonal platelets having planar defects parallel to large (111) faces. We suggest that at 500°C fullerene particles are partially vaporized forming residuals with lamellar defects such as twins and stacking faults, which promote crystal growth during synthesis. Subsequently fullerene vapor is condensed on faces with defects and hexagonal particles are grown by a re-entrant corner growth mechanism. At 600°C particles are single crystals, but they have a less distinct shape due to higher vaporization of fullerene. The final size and shape of the particles are mainly determined at the reactor outlet in the short time when the aerosol cools.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1010089628868

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Structural investigations of recently discovered high Tc superconductors (1995)

Van Tendeloo, G. ; Krekels, T. ; Amelinckx, S. ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Microscopy Research and Technique 30 (1995), S. 102-122

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ISSN: 1059-910X

Keywords: High Tc ; Superconductors ; Deformation modulations ; Oxygen ordering ; Superstructures ; YBCO ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Natural Sciences in General

Notes: A short overview is given of the possibilities of electron microscopy in the determination of the local, atomic scale structure of high Tc superconducting materials. Examples include the detection of weak oxygen ordering, description and characterization of deformation modulations in layered superconductors, and analysis of very long period superstructures. The ordering principles for tetrahedral chains in Ga-, Co-, or Al-substituted YBCO are discussed and their complex defect structures are described. The incommensurate modulation in YBCO-based materials containing SO4-tetrahedra, centered on the Cu(1) sites of the CuO-chain plane is attributed to the ordering of b-oriented SO4-rich chains in the Cu(1)-S-O layer; the structure is described in terms of an SO4-concentration wave. As examples of the new mercury-based superconducting family we discuss Y0.6Ca0.4Ba2Hg1-xMxCu2O6+y, which crystallizes in the space group P4/mmm with a = 0.3870(1) nm, c = 1.2537(1) nm. This cuprate belongs to the 1212 series; susceptibility measurements show a Tc (onset) of 90K, with a diamagnetic volume fraction of 27% at 4.2K to be reached. A second example is related to the compound Tl2HgBa4Cu2O10+y, in which ordering between single Hg layers and double Tl layers is observed. © 1995 Wiley-Liss, Inc.

Additional Material: 24 Ill.