Un método de suma de valencia de enlaces para identificar nuevos conductores de iones de fluoruro

The bond valence sum (BVS) method has been extensively used to probe the ionic diffusion pathways within solids possessing high ionic conductivities, both anionic and cationic. For the former, the presence of lone-pair cations such as Tl⁺, Sn²⁺, Pb²⁺, Sb³⁺ and Bi³⁺ is known to enhance the anionic conductivity of solids by promoting disorder within the anion substructure and lowering the energy barriers between lattice sites. However, the BVS formalism assumes spherical ions and does not include the possibility of the more irregular co-ordination environments associated with electron lone pairs. We present here a simple modification of the BVS approach, which has been implemented in the form of a Python program that permits the preferred F^- diffusion pathways to be determined in fluoride ion conductors containing lone-pair cations. The method has been benchmarked by calculating energy barriers that broadly correlate with the F^- ionic conductivities of known compounds, and successfully reproduces the F^- distribution within the highly conducting compound β-PbSnF₄ determined by neutron powder diffraction and molecular dynamics (MD) methods. Using this new approach, fluoride compounds within the Inorganic Crystal Structure Database that contain at least one lone-pair cation have been screened and several new potential F^- ion conductors have been identified.