A neutron diffraction study of yttrium- and lanthanum-aluminate glasses.
Journal of Non-Crystalline Solids
143 - 155.
Neutron diffraction data for three aluminate glasses have been collected for a range of scattering vector from 0.3 to 25 Å. A single phase glass, representing the high-density glass polymorph of yttrium-aluminate (AY25) composition has a structure resembling that of levitated YAG liquid. This glass has a first-neighbor Al-O distance of 1.82 Å and a first-shell coordination number of 4.16 ± 0.21. The Y-O distance is represented by a single Gaussian peak centered at 2.28 Å which yields a first-neighbor coordination number of 6.64 ± 0.33. These values indicate an increase in volume on melting of YAG solid solution. An equivalent lanthanum-aluminate glass (La25), also produced from the stable high-temperature aluminate liquid, has an Al-O distance of 1.79 Å and a coordination number of 4.55 ± 0.23. The La-O distance is increased due to an increase in ionic radius for La(III). The magnitude of this La-O peak is lower than expected and there is evidence for a second La-O distance at 2.79 Å. The T(r) for the lanthanum-aluminate glass shows stronger features than the yttrium-aluminate glass at radial distances greater than 3 Å; these suggest a higher degree of order in the lanthanum-aluminate liquid. A two-phase yttrium-aluminate (AY20) glass, which represents a partly complete transition between a high-density liquid and a lower density polymorph, has an Al-O distance of 1.81 Å and a mean Al-O coordination number of 4.38 ± 0.22. There is an increase in the Y-O radial distance on transition and also additional mid-range ordering. This mid-structure is similar to that seen in the La25 glass. The data show that rare earth aluminate liquids are dominated by a tetrahedral aluminate framework and that the liquid-liquid (transition) in the yttrium-aluminate liquids results from differences in packing among AlO and Y-O polyhedra and not from a change in the mean Al-O coordination number. © 2002 Elsevier Science B.V. All rights reserved.
|Title:||A neutron diffraction study of yttrium- and lanthanum-aluminate glasses|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry|
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