Structure of ultraphosphate glasses with small rare-earth ions by X-ray diffraction

Abstract

Rare-earth ultraphosphate glasses with nominal R 2O 3 fractions of 10 and 15 mol% and small ionic radius (large atomic number) R 3+ ions ( R = Tb, Tm, Lu) are measured by X-ray diffraction at a synchrotron with photons of 119 keV (maximum scattering vector 260 nm − 1 ). The total correlation functions T( r) show well-resolved R–O and O–O first-neighbor peaks. In contrast to all ultraphosphate RP 5O 14 crystals and the ultraphosphate glasses of larger R 3+ ions, where RO 8 polyhedra (mean R–O coordination numbers of ~ 8 for the glasses) are observed, the R 3+ ions in glasses with R = Lu, Tm, Tb have mean R–O coordination numbers of ~ 7.5. The R–O first-neighbor peaks extracted from the T( r) functions are compared with those obtained from atomic coordinates of related RP 5O 14 and RP 3O 9 crystals. The R–O distances of the ultraphosphate glasses studied are found to fall between those of the two crystals but with tails to the side of longer bonds.