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'short range order' in keywords Facet   Publication Year 1998  [X]
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1Author    Uwe Hoppe, Günter Walter, Rainer Kranold, Dörte StachelRequires cookie*
 Title    An X-ray Diffraction Study of the Structure of Vitreous P2O5  
 Abstract    Recently, the lengths of the two P-0 bonds in the P0 4 tetrahedron were obtained by neutron diffrac-tion of high real-space resolution. By use of the present X-ray diffraction experiments, the P-P distance belonging to pairs of corner-linked P0 4 units is determined. Using this length of (294 ± 2) pm and tak-ing into account the P-0 bond distance to the bridging oxygen atom of 158 pm, a mean P-O-P angle of 137° ± 3° is calculated. The reverse Monte Carlo simulations fit the neutron and X-ray structure fac-tors. The P-O-P angle distribution obtained this way possesses a mean angle of 141°. An interpretation of the first scattering peaks is presented by analysing the occupancy and the distances of various co-ordination shells by use of model configurations. The low occupancy of the first shells allows the ap-plication of the schematic hole model of Dixmier. The first X-ray diffraction peak at 13 nra" 1 is related to the P-P2nd shell, the shoulder at 20 nm -1 arises from the P-0 2nd shell. The most similar crystalline structure with vitreous P2O5 is the orthorhombic P2O5, form II. But it has more effectively orientated terminal oxygen atoms and, thus, a higher packing than the glass. 
  Reference    Z. Naturforsch. 53a, 93—104 (1998); received December 22 1997 
  Published    1998 
  Keywords    Vitreous P 2 0 5, X-ray Diffraction, Short-range Order, Reverse Monte Carlo 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0093.pdf 
 Identifier    ZNA-1998-53a-0093 
 Volume    53 
2Author    G. Herms, J. Sakowski, W. Gerike, Dörte StachelRequires cookie*
 Title    Structural Changes in Two Different Types of Oxide Glass Melts: Borates and Metaphosphates  
 Abstract    X-ray diffraction experiments of molten oxide glasses, which give new insights into the structure of melts, were carried out. Using modern means (synchrotron radiation, image plates, container-less high-temperature technique) it could be shown that the short range order of melt and solid glass is often qual-itatively different. If vitreous B 2 0 3 or binary borate glasses with low content of network modifier are heated up above T & , the network topology begins to alter. With rising temperature more and more of the boroxol groups are replaced by independent B0 3 groups. While melting a metaphosphate glass, how-ever, structural changes of another kind take place. In solid glass the environment of the network mod-ifier ions is similar to the one found in crystalline modifications, and their distances to the surrounding P0 4 tetrahedra have narrow distributions. In the melt, however, these distances scarcely become evi-dent, probably owing to the increased thermal motion of the modifier ions. 
  Reference    Z. Naturforsch. 53a, 874—882 (1998); received February 17 1997 
  Published    1998 
  Keywords    X-ray Diffraction, Short Range Order, Borate Glasses, Phosphate Glasses, Glass Transition 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0874.pdf 
 Identifier    ZNA-1998-53a-0874 
 Volume    53