Zinc environment in aluminoborosilicate glasses by Zn K-edge extended x-ray absorption fine structure spectroscopy
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amos Laboratoire de Mine´ralogie et de Cristallographie, Universite´ Paris VI et VII, CNRS-UMR7590, 75252 Paris Cedex, France and Laboratorio Nacional de Luz Sincrotron, CP 6192, 13083-970 Campinas, Brazil
G. Calas and L. Galoisya) Laboratorie de Mine´ralogie et de Cristallographie, Universite´ Paris VI et VII, CNRS-UMR7590, 75252 Paris Cedex, France
D. Ghaleb and F. Pacaud Commissariat a` l’Energie Atomique, Marcoule, Rhoˆne Valley Research Center, Commissariat a` l’Energie Atomique, Marcoule, 30207 Bagnols/Ce´ze Cedex, France (Received 6 August 1999; accepted 26 June 2000)
The structural surrounding of Zn in inactive nuclear glasses was determined using extended x-ray absorption fine structure spectroscopy. Zn was found in tetrahedral coordination ([4]Zn) with [4]Zn–O distances of 1.95 Å. ZnO4 tetrahedra shared corners with SiO4 tetrahedra [d(Zn–Si) around 3.20 Å]. The oxygens of the Zn–O–Si bonds were charge compensated by Na+ and, to a minor extent, by Cs+. The influence of [4] Zn on the formation of charge-compensating cations at the expense of network modifiers may explain the stabilizing effect of Zn in these glasses. I. INTRODUCTION
The French aluminoborosilicate light water waste containment glass is composed of more than 30 elements and is used to immobilize fission products and transuranic elements. The glass frit used to vitrify the calcined highactivity solutions contains significant amounts of Zn (0.64 at.% in the final glass), because it improves the glass quality. In alkali silicate glasses, Zn usually increases the mechanical properties, when in low proportion (4 3.0(5) 3.8(4)
Glass composition
0.11(1) 0.09(5)
R (Å)
(Å)
N
≈3.2 3.25–3.33 >3.00 3.25(2) ≈3.2
0.14(1)
3.5(5)
Backscatterer mainly Si Si Si Si,Al,Mg Si,B
J. Mater. Res., Vol. 15, No. 9, Sep 2000
http://journals.cambridge.org
Downloaded: 13 Mar 2015
Ref. 25 7 7 3 17
2017 IP address: 131.170.6.51
M. Le Grand et al.: Zinc environment in aluminoborosilicate glasses by Zn K-edge EXAFS spectroscopy
One must be careful when discussing the environment above the coordination shell as derived from EXAFS spectroscopy. Indeed certain atoms, such as B, alkalis, and earth alkalis, may not be detected by EXAFS because of a strong structural disorder and/or because these scatter very weakly. However, some insight on the Zn environment beyond the coordination shell can be obtained by using the bond valence model.12,22 According to this model, the sum of the bond valences relative to an oxygen must be close to the theoretical value of 2.0 valence units (i.e., 2.0 ± 0.1 v.u.). The valence of a M–O bond, labeled s, is calculated using the following relationship: s ⳱ e(Ro − R)/0.37 , where R is the M–O bond distance and Ro the bond valence parameter for M, which is tabulated in Ref. 22 for most cations in different valence states. The Zn–O bond valence at room temperature calculated using the EXAFS-determined interatomic Zn–O distance, is 0.5 v.u., which corresponds to the expected value for divalent Zn in tetrahedral coordination. As for m
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