An X-ray Diffraction Study of the Structure of Vitreous P2O5

Abstract

Recently, the lengths of the two P-0 bonds in the PO4 tetrahedron were obtained by neutron diffraction of high real-space resolution. By use of the present X-ray diffraction experiments, the P-P distance belonging to pairs of comer-linked PO4 units is determined. Using this length of (294 ± 2) pm and taking into account the P-0 bond distance to the bridging oxygen atom of 158 pm, a mean P-O-P angle of 137° ± 3° is calculated. The reverse Monte Carlo simulations fit the neutron and X-ray structure factors. The P-O-P angle distribution obtained this way possesses a mean angle of 141°. An interpretation of the first scattering peaks is presented by analysing the occupancy and the distances of various coordination shells by use of model configurations. The low occupancy of the first shells allows the application of the schematic hole model of Dixmier. The first X-ray diffraction peak at 13 nrrT1 is related to the P-P2nd shell, the shoulder at 20 nm-1 arises from the P-02nd shell. The most similar crystalline structure with vitreous P2O5 is the orthorhombic P2O5, form II. But it has more effectively orientated terminal oxygen atoms and, thus, a higher packing than the glass. © 1998, Verlag der Zeitschrift für Naturforschung. All rights reserved.