Structure of Zinc Phosphate Glasses of 75 and 80 mole% ZnO Content Studied by X-Ray Diffraction and Reverse Monte Carlo Simulations

X-Ray diffraction, using high-energy photons from a synchrotron, was used to extend the investigation of (ZnO) (P glasses to samples of ZnO content close to x = 0.8 which were obtained by roller-quenching. The isolated PO tetrahedra are surrounded by ZnOn polyhedra, where Zn−O coordination numbers of ∼ 4.5 are determined. The small increase of NZnO from ∼ 4 at metaphosphate composition (x = 0.5) to ∼ 4.5 is not sufficient to explain the strong increase of the packing density beyond the minimum at x = 0.5. The medium-range order was analyzed on the basis of partial S (Q) and S (Q) factors obtained from Reverse Monte Carlo simulations of glasses with 0 ≤ x ≤ 0.8. The positions of the first peaks in these factors, the number densities of P and Zn atoms and knowledge of definite P-P and Zn-Zn distances were used to check the applicability of simple models such as the dense packing of uniform P- and Zn-centered spherical environments for glasses with x=0.8 and 0.5, the packing of corrugated sheets for vitreous P and the packing of phosphate chains for Zn metaphosphate glass.