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1Author    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 
2Author    Uwe Hoppe3, Günter Walter8, Dörte Stachelb, AlexC. HannoncRequires cookie*
 Title     
 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    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 
4Author    E. Sváb, F. Hajdu, Gy MészárosRequires cookie*
 Title     
 Abstract    e m i-E m p iric a l F ittin g o f P a r t i a l P a i r C o r r e la tio n F u n c tio n s o f A m o rp h o u s A llo y s A semi-empirical fitting procedure has been developed and used in analysing the characteristic features of the partial structure factors of binary amorphous alloys. An analytical formula is given to fit the experimental atomic pair correlation function as a sum of Gaussians. The inverse Fourier transform of the fitted terms reproduces all features of the experimental structure function. In addition to the structural parameters, the modelling gives a quantitative explanation for the complex origin of characteristic features in the diffraction pattern such as pre-peak, pre-minimum, and split peaks in the partial structure factor. 
  Reference    Z. Naturforsch. 50a, 1205—1210 (1995); received September 22 1995 
  Published    1995 
  Keywords    Metallic glass, Short range order, Partial correlations, Neutron diffraction, Fitting 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-1205.pdf 
 Identifier    ZNA-1995-50a-1205 
 Volume    50 
5Author    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 
6Author    Walter Hoyer, Hartmut Neumann, Manfred WobstRequires cookie*
 Title    Structure Investigation on Liquid Tellurium by X-Ray and Neutron Scattering  
 Abstract    We present the results of neutron and X-ray scattering experiments on liquid tellurium. No dependence on temperature of the radius and the coordination number of the first neighbour shell has been found in the temperature range between 460 °C and 550 °C. We investigate the influence of the truncation of the Fourier transformation on the determined coordination number of nearest neighbours and on the shape of the second coordination maximum at both, the lower and upper integration limit. The structure of liquid tellurium can be described in terms of a chain-like atomic arrangement with two bonds per atom. 
  Reference    Z. Naturforsch. 47a, 833—840 (1992); received May 8 1992 
  Published    1992 
  Keywords    Neutron scattering, X-ray scattering, Short-range order, Liquid tellurium, Termination effect 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0833.pdf 
 Identifier    ZNA-1992-47a-0833 
 Volume    47 
7Author    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 
8Author    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 
9Author    Hartmut Neumann, Walter Hoyer, Manfred WobstRequires cookie*
 Title      
 Abstract    From neutron and X-ray diffraction investigations on liquid Ge15Te85, Sn16Te84 and Pb14 5Te85 5 alloys the coordination numbers and nearest neighbour distances of these systems are obtained. The partial structure factors and partial pair correlations reveal that the short-range order of the eutectic Ge-Te melt differs from that of the eutectic Sn-Te and Pb-Te melts. 
  Reference    Z. Naturforsch. 46a, 739 (1991); received June 19 1991 
  Published    1991 
  Keywords    Neutron scattering, X-ray scattering, short-range order, liquid alloys, eutectic Ge-Te, Sn-Te and Pb-Te melts 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-0739.pdf 
 Identifier    ZNA-1991-46a-0739 
 Volume    46