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1Author    M. Born, C. Feike, H. W. Jäger, SpiessRequires cookie*
 Abstract    Dedicated to Prof. W . Müller-Warmuth on the occassion of his 65th birthday Recently, 31P two-dimensional (2D) NMR has been proposed as a powerful tool for direct investigations of the connectivities between the Q" units in glasses, i.e. the medium-range order. In this paper, the principles of these experiments and applications to both polycrystalline Mg2P20 7 and a Na20 -P 2C>5 glass are demonstrated, including a theoretical description and modelling of the polarization transfer between the two inequivalent phosphorus sites in the magnesium pyrophos­ phate. 2 D 31P E x c h a n g e N M R : A new A p p r o a c h f o r a D ir e c t P r o b in g o f th e C o n n e c tiv itie s o f Q 1 U n its in G la s s e s 
  Reference    Z. Naturforsch. 50a, 169—176 (1995); received September 26 1994 
  Published    1995 
  Keywords    Exchange NMR, Connectivities, Phosphate glasses, Dipolar coupling, MAS 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0169.pdf 
 Identifier    ZNA-1995-50a-0169 
 Volume    50 
2Author    Uwe Hoppe3, Günter Walter8, Dörte Stachelb, AlexC. HannoncRequires cookie*
 Abstract    h o r t-R a n g e O r d e r D e ta ils o f M e ta p h o s p h a te G la s s e s S tu d ie d b y P u ls e d N e u tr o n S c a tte r in g Details of the short-range order of the binary metaphosphate glasses A1P30 9 and PbP2Oe and the ternary glass system ZnO-MgO-2P2Os have been studied by pulsed neutron scattering which provides a measuring range up to about ß m ax = 500 nm-1. The splitting of the P-O peak in the distance correlation functions attributable to the different bond lengths for the non-bridging and bridging oxygens was found to decrease with increasing field strength of the network-modifier cations. For the ternary system ZnO-MgO-2P2Os the peak in the distance correlation function, T(r), produced by the first oxygen neighbours around Zn2+ and Mg2+ was separated by the additional use of the X-ray structure factor. The distances rZn0 and rM gQ extracted from the separated peaks are slightly different from those obtained from the binary glasses ZnP20 6 and MgP20 6. The metal-oxygen coordination numbers were found to be NZn0=4.5 and NM g0 = 5.5. For the two binary systems the coordination numbers Al-0 and Pb-0 were obtained to be 7 and 5, respectively. 
  Reference    Z. Naturforsch. 50a, 684—692 (1995); received March 6 1995 
  Published    1995 
  Keywords    Pulsed neutron scattering, phosphate glasses, short-range order 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0684.pdf 
 Identifier    ZNA-1995-50a-0684 
 Volume    50 
3Author    Uwe Hoppe, Rainer Kranold, Dörte Stachel, Andrea Barz, AlexC. HannonRequires cookie*
 Title    Variation in P-O Bonding in Phosphate Glasses -A Neutron Diffraction Study  
 Abstract    Two different lengths of P-0 bonds in the P0 4 units of phosphate glasses are found by neutron diffraction experiments of high resolution in real space. The two lengths are related to bonds of the phosphorus atom with the terminal and the bridging oxygen atoms. The mean lengths and widths of both P-0 distance peaks change as a function of the glass composition. In a large range, starting from vitreous P 2 O s up to the pyrophosphate composition, the behavior of the bond lengths is compared with that in the related crystals and with that resulting from ab initio calculations. The bond lengths depend not only on the species of the participating oxygen atoms and on the number of links of the concerning P0 4 unit but also on the number of links of the neighboring P0 4 unit and on the species of the modifier cation. 
  Reference    Z. Naturforsch. 55a, 369—380 (2000); received October 6 1998 
  Published    2000 
  Keywords    Neutron Diffraction, Short-range Order, Phosphate Glasses 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0369.pdf 
 Identifier    ZNA-2000-55a-0369 
 Volume    55 
4Author    Uwe Hoppe, Günter Walter, Dörte Stachel, Andrea Barz, AlexC. HannonRequires cookie*
 Title    Neutron and X-ray Diffraction Study on the Structure of Ultraphosphate Glasses  
 Abstract    The high real-space resolution of neutron diffraction experiments which is provided by use of the epithermal neutrons from spallation sources was exploited in order to differentiate the unlike P-O bonds existing in the P0 4 units of phosphate glass networks. The 2 P-O distance peaks, separated by about 12 pm, which were found in the zinc and the calcium ultraphosphate glasses studied are assigned to oxygen sites on bridging (O b) and terminal (O X) positions. The mean P-O distances are nearly invariable versus the growing metal oxide content which results from an elongation of the P-O b and P-O t bonds. The bond lengths which are known from the related crystal structures and from ab initio calculations show almost the same behaviour. The discussion of further details of the crystal structures leads to the conclusion that P-O b rather than P-O t distances should show more details in case of diffraction measurements of even higher real-space resolution. The change of the Zn-O coordination number from 6 to 4 versus increasing ZnO content, which was obtained in previous X-ray diffraction experiments, is confirmed by the recent combination of neutron and X-ray diffraction data. On the other hand, the Ca-O coordination number of about 6 is almost invariable. 
  Reference    Z. Naturforsch. 52a, 259—269 (1997); received July 6 1996 
  Published    1997 
  Keywords    Neutron diffraction, X-ray diffraction, Phosphate glasses, Short-range order 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0259.pdf 
 Identifier    ZNA-1997-52a-0259 
 Volume    52 
5Author    Z. NaturforschRequires cookie*
 Title    A Neutron and X-ray Diffraction Study of the Structure of Nd Phosphate Glasses  
 Abstract    Diffraction experiments were performed on two (Nd203)x(P205)i_ x glasses for studying the en­ vironmental order of the Nd3+ cations. In case of the metaphosphate glass (x = 0.25) a combination of X-ray and neutron diffraction data was used to separate the N d-0 and 0 -0 first neighbor peaks. An N d-0 coordination number of 6.6±0.3 and a mean N d-0 distance of (0.239±0.001) nm were determined. In the ultraphosphate glass studied (x = 0.20) these values increase to 6.9±0.3 and (0.240±0.001) nm where the N d-0 coordination number is equal to the number of terminal oxygen atoms (0 T) which are available for coordination of each Nd3+ cation. This indicates the formation of NdOn polyhedra not sharing any O atom where also all 0 T's are in N d-0T-P positions. In the metaphosphate glass the NdO" polyhedra have to share some 0 T sites. 
  Reference    Z. Naturforsch. 56a, 237—243 (2001); received January 8 2001 
  Published    2001 
  Keywords    Neutron Scattering, X-ray Scattering, Short-range Order, Phosphate Glasses 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0237.pdf 
 Identifier    ZNA-2001-56a-0237 
 Volume    56 
6Author    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