Structure of silver molybdate glasses by X-ray and neutron diffraction

Abstract

The structure of (Ag2O)x(MoO3)1-x glasses of 0.2 ≤ x ≤ 0.4 is studied by combining X-ray and neutron diffraction which allows separating the Mo-O and Ag-O distances up to r ≤ 0.25 nm. The total Mo-O coordination numbers decrease from 5.4 to 4.2 with increasing x. This strong decrease and the excessive formation of non-bridging oxygen (NBO) require each other. A fixed ratio NBO/Oadd = 4.6 is a good approximation. Oxygen Oadd is added with the network-modifier oxide. The distributions of Mo-O distances show a sharp peak at 0.177 nm of three oxygen neighbors that is followed of a broad distribution with one to three more oxygens. Mixtures of MoO6, MoO5, and MoO4 are used to model the distance distributions. Their strong broadening is caused by the second-order Jahn-Teller effects in the MoO6 octahedra with out-of-center displacements of the Mo sites preferably to edges.