Glass formation and local structure in the ternary system P-Se-Al. Solid state NMR studies

Glasses in the system phosphorus-selenium-aluminum have been prepared by ice-water quenching of sealed ampoules. X-ray powder diffraction and differential scanning calorimetry (DSC) of samples indicate a limited region of glass formation a in the selenium-rich region of the composition diagram. Structural studies using Al-27 and P-31 solid state NMR reveal that the local environments of both aluminum and phosphorus are dominated by selenium, however, multiple environments are observed for both glass constituents. The presence of aluminum enhances the tendency of phosphorus to become four-coordinate, suggesting that both glass formers interact in the network to some extent. On the other hand, dipolar solid state NMR studies indicate that the P ... Al interactions are generally smaller than expected on the basis of statistically linked PSex and AlSex polyhedra. Together with DSC results, these data favor a structure that is at least partially segregated and/or phase separated. (C) 1998 Elsevier Science B.V.