REVERSE MONTE-CARLO MODELING OF EU AND TB METAPHOSPHATE GLASSES

It is possible to make phosphate glasses (R2O3)(x)(P2O5)(1-x) With con tents of rare-earth elements, R, close to the metaphosphate compositio n, R(PO3)(3). These glasses are particularly stable to water, and have interesting optical, acoustic and magnetic properties. We have modell ed Eu and Tt, metaphosphate glasses using the reverse Monte Carlo (RMC ) technique with X-ray diffraction data. The model building process mu st include additional constraints, and we have derived these from know ledge of metaphosphate structures, including metaphosphate crystals. T he model building procedure was first to fit structural constraints al one, and then to fit the diffraction data while maintaining the struct ural constraints. The models constructed consist of chains of phosphat e tetrahedra with Eu (or Tb) 6-fold coordinated to non-bridging oxygen s (NBOs), and are in good agreement with the diffraction data. Thus th e models provide a demonstration of validity of this structural descri ption of rare-earth metaphosphate glasses. In addition, two different values were used for minimum rare-earth separation, 3.9 and 5.4 Angstr om, based on two different metaphosphate crystals, and more satisfacto ry models were obtained when using the shorter distance. (C) 1998 Else vier Science B.V. All rights reserved.