Reverse Monte Carlo and Rietveld modelling of the NaPbM2F9 (M=Fe, V) fluoride glass structures

Fluoride glasses with a nominal composition of NaPbM2F9 (M = Fe, V, assuming isomorphous replacement) have been structurally modelled through the simultaneous simulation of their neutron and X-ray diffraction patterns by a reverse Monte Carlo (RMC) model and by a Rietveld for disordered materials (RDM) method. Models and methods are discussed and compared. Models are consistent with an expected network of interconnected [MF6] polyhedra. Those polyhedra are exclusively octahedral by the RDM method, and both trigonal prisms and octahedra, which are more or less distorted, by the RMC approach.