Medium range order around cations in silicate glasses

Structural role of Zr4+ as a nucleating agent in a MgO–Al2O3–SiO2 glass-ceramics: A combined XAS and HRTEM approach

“…This suggests an inhomogeneous distribution of Zr 4+ within the glass. Such an evidence of local organization within oxide glasses has already been shown for cations such as Ti or Ni [45,46]. This suggests that the inhomogeneous distribution of Zr corresponds to the formation of locally ordered domains.…”

Structural study of Ca–Mg and K–Mg mixing in silicate glasses by neutron diffraction

“…The melt viscosity in the Ca-Mg system exhibit a non-linear variation that can be well reproduced by a model of configurational entropy assuming a random mixing of Ca and Mg [34]. Here too, the Mg-Ni analogy is interesting: a neutron diffraction with isotopic substitution has been performed on a mixed Ca 2 NiSi 3 O 9 glass [6] showing a Ca-Ni mixing, with cationic sites belonging to corrugated sheets.…”

“…The first description of the glass structure [1,2] assumed a random distribution of these cations, filling the interstices of the network formed by cornersharing of SiO 4 tetrahedra and breaking the connectivity of the silicate network to form non-bridging oxygen (NBO). This schematic glass representation was experimentally dismissed based on EXAFS measurements [3,4] which were latter confirmed by neutron diffraction with isotopic substitution [5][6][7]. A non-random distribution of the cations is shown in these studies, with separate regions rich either in Si or in modifier cations.…”

La structure des verres étudiée par diffraction des neutrons

“…La diffraction anomale des rayons X et la diffraction des neutrons avec substitution isotopique sont des méthodes chimiquement sélectives, comme l'EXAFS, mais elles ont l'avantage de pouvoir sonder la structure sur de plus grandes distances (typiquement 10 Â) et avec une meilleure précision [50]. L'utilisation de matériaux substitués isotopiquement permet d'obtenir une information similaire à la diffraction anomale des rayons X mais pour des éléments différents, avec une meilleure statistique expérimentale et la possibilité d'extraire directement les distances cations-cations.…”