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1Author    G. Ennas, A. Musinu, G. Paschina, G. Piccaluga, G. PinnaRequires cookie*
 Title    Effect of Cooling Rate on the Structure of Sodium Borate Glasses  
 Abstract    Sodium borate glasses with two different compositions have been prepared using cooling rates in the range 7 • 10" C/s-2 • 10 2 °C/s. Structural characterization has been carried out by X-ray diffraction, and glass transition temperatures have been measured by Differential Scanning Calorimetry. The samples exhibit slightly different density values and glass transition temperatures. However, radial distribution functions appear extremely similar and the sodium coordination shell does not change in going from fast to slowly quenched glasses, showing that the short and medium range order is not affected by thermal treatment. 
  Reference    Z. Naturforsch. 48a, 599—604 (1993); received January 19 1993 
  Published    1993 
  Keywords    Glass, structure, diffraction 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0599.pdf 
 Identifier    ZNA-1993-48a-0599 
 Volume    48 
2Author    R. BlincRequires cookie*
 Title    NQR in Dipolar and Quadrupolar Glasses  
 Abstract    It is shown that nuclear quadrupole resonance and quadrupole perturbed magnetic resonance represent a powerful technique to determine the local polarization distribution and its second moment, the Edwards-Anderson order parameter, in proton and deuteron glasses. For quadrupolar glasses the local orientational distribution function can be determined from the inhomogeneous NMR or NQR lineshape, thus allowing for a measurement of the quadrupolar Edwards-Anderson order parameter. The comparison of the temperature dependences of the thus obtained order parameters with theoretical predictions then allows for a discrimination between the different possible models of the glassy transition. 
  Reference    Z. Naturforsch. 45a, 313—322 (1990); received August 22 1989 
  Published    1990 
  Keywords    NQR, Glasses, Order parameters 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0313.pdf 
 Identifier    ZNA-1990-45a-0313 
 Volume    45 
3Author    Piercarlo Mustarelli, Corrado Tomasi, Marco Villa, C.S T E, -CN R AndRequires cookie*
 Title    Heat Capacities of Thermally Treated Na 2 0-3B 2 0 3 Glasses Above and Below T g  
 Abstract    Various contributions have been obtained from the heat capacities of "as quenched" and annealed Na 2 0-3 B 2 0 3 glasses. It is shown that the enthalpic release gives a major contribution to the DSC curves obtained by reheating quenched glasses. Different relaxation processes are followed by comparing DSC scans of quenched and annealed samples in the vitreous state and around the glass transition temperature, 7^. As a function of the annealing time at T = T g — 30 "C, the specific heats at room temperature initially increase, due to the decrease of the exothermic contribution from quenched-in defects, which are absent in a fully annealed glass; over a month-long time scale these heat capacities drop, due to a partial ordering, which decreases the configurational contribution. Such a decrease is related with the "overshoot" which occurs above and which attains a limiting value AH g s 14 J moP 1 in a matter of days. The heat capacities above T g relax towards a value of C P of = 2.3 J mol" 1 K~ 1 after a few days of annealing, which is intermediate between the anomalously low C P (~ 1.8 J mol" 1 K _1) of a fast quenched (~10 3 Kmin _1) and that (~2.9J mol" 1 K" 1) of a sample annealed for one hour. These phenomena point to complex relationships among enthalpic relaxation, entropic relaxation and temperature in these glasses. 
  Reference    Z. Naturforsch. 51a, 187—191 (1996); received January 11 1996 
  Published    1996 
  Keywords    Glasses, borates, structural relaxation, annealing 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0187.pdf 
 Identifier    ZNA-1996-51a-0187 
 Volume    51 
4Author    T. A. Mirnaya, V. S. Dradrah, G. G. YaremchukRequires cookie*
 Title    Mesophase and Glass Formation in Binary Systems of Caesium and Alkali-Earth Metal Butyrates  
 Abstract    The phase diagrams of the binary systems of non-mesomorphic components such as caesium-mag-nesium, caesium-calcium and caesium-barium butyrates have been studied by differential thermal analysis and hot stage polarization microscopy. Smectic liquid crystals are found in some composition ranges of the binaries with calcium and barium butyrates. The liquid crystal appearance in these systems is explained by the exhibition of latent mesomorphism of caesium butyrate. Glasses are obtained in all systems studied, the formation of vitreous optical anisotropic mesophase being revealed only for binary from caesium and barium butyrates. 
  Reference    Z. Naturforsch. 54a, 685—688 (1999); received October 19 1999 
  Published    1999 
  Keywords    Phase Diagram, Mesophase, Glass, Metal Alkanoate 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0685.pdf 
 Identifier    ZNA-1999-54a-0685 
 Volume    54 
5Author    G. Kunath-Fandrei1, D. Ehrt2, C. Jäger3Requires cookie*
 Abstract    r o g r e s s in S t r u c t u r a l E lu c id a tio n o f G la s s e s b y 27A1 a n d n B S a te llite T r a n s itio n N M R S p e c tr o s c o p Dedicated to Prof. Dr. W . Müller-Warmuth on the occasion of his 65th birthday The structure of Na20-A l20 3-B203 and Na20-A l20 3-P 20 5 glasses with 70 mole% B20 3 or P2Os and varied Na/Al ratio is investigated using standard 31P MAS NMR and 27A1 and UB Satellite Transition NMR spectroscopy. The role of the two network formers on the glass structure is discussed. For the A10x units and B03 and B04 groups both chemical shifts and quadrupole interaction parameters including their distribution widths are reported. Besides this, the advantages of Satellite Transition spectroscopy are demonstrated both for 27A1 and n B NMR. 
  Reference    Z. Naturforsch. 50a, 413—422 (1995); received December 16 1994 
  Published    1995 
  Keywords    NMR, Glass, Structure, Satellite Transition, 11B, 27A1, 31 P 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0413.pdf 
 Identifier    ZNA-1995-50a-0413 
 Volume    50 
6Author    H. Yoshida, H. Nishihara, S. Yokota, M. Ohyanagi, T. NakaokiRequires cookie*
 Title    Field-Swept NMR Spectra of n B in Pyrex Glass and 93 Nb in NbN Perturbed by Quadrupole Interaction  
 Abstract    NMR experiments of "B by both field-swept and high-resolution NMR are reported to probe the electric field gradient at boron sites and its distribution in Pyrex glass. Both spectra are successfully interpreted with the same set of parameters. It is stressed that field-swept NMR experiments to observe total powder spectrum can be helpful to get information on electric field gradients and asymmetry pa-rameters if there exist many nonequivalent sites of atoms, since satellite transitions are affected by the larger first-order quadrupole effect. Field-swept NMR of 93 Nb in superconducting NbN powder, pre-pared by self-propagating high-temperature synthesis, is also reported. A very broad field-swept spec-trum disturbed by quadrupole interaction has been observed. The spectrum is simulated by assuming distributions in electric field gradient and Knight shift at Nb sites. It is stressed that a combination of experiments at separated frequencies is important 
  Reference    Z. Naturforsch. 53a, 309—313 (1998); received January 26 1998 
  Published    1998 
  Keywords    NMR, Pyrex, Glass, n B, NbN, Superconductor, 93 Nb 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0309.pdf 
 Identifier    ZNA-1998-53a-0309 
 Volume    53