A refined reverse Monte Carlo analysis of the structure of vitreous P₂O₅

The improved reverse Monte Carlo simulations of the structure of vitreous P 2 O 5 are constrained by neutron and x-ray scattering data both covering large ranges of momentum transfer, and by geometric constraints which are different for the terminal and bridging oxygen sites. The analysis of the model structures reveals the anisotropy of the threefold-linked PO 4 tetrahedra with different P-O bonds and O-O edges of the terminal and bridging oxygen sites. The O-P-O and P-O-P bond angles possess mean values of 109 and 139°. Flattened network cages formed of the P atoms and the bridging O sites are identified in the models. Their formation is enhanced by the more real geometry of the PO 4 units. The first peak of the x-ray and neutron diffraction data is related to the lateral dimension of the cages of about 0.47 nm.