²⁷Al NMR Study of the Structure of Lanthanum- and Yttrium-Based Aluminosilicate Glasses and Melts

Abstract

We have investigated by (27)Al nuclear magnetic resonance spectroscopy some compositions in the Ln(2)O(3)-Al(2)O(3)-SiO2 (Ln = Y or La) ternary phase diagram containing more than 60 mol % of SiO2. One- and two-dimensional high-field (17.6 T) high-speed (30 kHz) magic angle spinning experiments have been performed along with simulations of the spectra to quantify the amount of penta-coordinated aluminum present in those glasses as a function of composition. Very high-temperature experiments have allowed to follow selected samples from 2200 degrees C down to 1700 degrees C and hence to characterize the aluminum coordination state and dynamics in those liquids. The present study re-enforces the current view that "minor" species such as penta-coordinated aluminum are actually present in a considerable amount in aluminosilicate glasses, and high-temperature liquids at and above the charge compensation join. The high-field strength of Y3+ and La3+ reveal, for the first time in glasses, a different mean electric field gradient perceived by the tetra- and penta-coordinated aluminum environments. The movements responsible for the NMR relaxation of aluminum in the high-temperature liquid are shown to be uncorrelated with the movements responsible for the macroscopic shear viscosity. Results obtained both on glasses and in situ at high-temperature suggest a preferential localization of Ln3+ nearby tetra-coordinated aluminum species, with possible formation of tricluster and/or Ln3+ coordination changes.

Short‐Range Structure of Yttrium Alumino‐Silicate Glass for Cancer Radiotherapy: Car–Parrinello Molecular Dynamics Simulations

“…An example of a five-coordinated Al atom is shown in the central panel of Figure 3. This is in agreement with NMR data on YAS [7,8] and related [14] glasses, which have consistently shown a range of Al coordination numbers from four to six, with four the most common. Diffraction experiments [6] gave an Al coordination number of 4.5 AE 0.5 for a glass with 11 mol% yttria, which is in agreement with the observed mean Al coordination number in the YAS17 glass, of 4.55.…”

“…limited amount of previous data on YAS glass, from computer simulation, [5] neutron, and X-ray diffraction, [6] NMR [7,8] and IR [9] spectroscopy, and none of these data concern the YAS17 composition. Also, much of this work has concentrated on the local structure around the silicon, aluminum, and oxygen ions; technical difficulties hinder NMR experiments that could address the yttrium local structure in this glass.…”

STRUCTURE, GLASS STABILITY AND RHEOLOGICAL PROPERTIES OF Na₂O-CaO-Al₂O₃-SiO₂ GLASSES DOPED WITH Y₂O₃

“…Aluminosilicate glasses doped with rare-earth elements have attracted large attentions because of their interesting physical and chemical properties, such like high glass transition temperature T g [1,2], high hardness and elastic modulus [3], excellent chemical [4,5] and thermal resistance [6], or high refractive index [7]. Therefore, these glasses have been widely used for optical communications, laser technology and other fields [2,8].…”

“…Therefore, these glasses have been widely used for optical communications, laser technology and other fields [2,8]. These excellent properties are closely related to their special structure characteristics.…”

“…In this work, the density, coefficient of thermal expansion and glass stability of Na 2 3 were labeled as Y0, Y1, Y2, Y3 and Y4, respectively. Glass batches were mixed thoroughly, and then melted in alumina crucibles at 1510~1530°C for 2 h. The part of melts were poured onto a pre-heated stainless steel mold to form, and then annealed at 50°C below their glass transition temperature T g for 2 h .…”