Density fluctuations in the network structure of AgI doped AgPO3 glass: The origin of the phonon-fracton crossover?

Abstract

Neutron diffraction studies of AgI doped AgPO3 glasses show the growth of a sharp diffraction peak at Q ≈ 0.7 Å −1 with increasing salt content, indicative of a change in intermediate range order. We show that this peak is due to local density fluctuations in the network of PO4 tetrahedra caused by the requirement to maintain connectivity while decreasing the average density. The phosphate backbone shows an inhomogeneous density distribution over regions of diameter ≈ 16 Å within which the number of atoms in a sphere of radius R increases at a rate lower than R3. It is proposed that this local inhomogeneity is related to the observation of a "phonon-fracton crossover" in the dynamics of similar glasses.