First-Principles Investigation of Anion Substitution in Vanadate and Titanate Pyrochlores

Pyrochlore oxides with chemical formula A₂B₂O₇, where the A- and B-site cations occupy corner-sharing tetrahedra, are well-known for hosting spin frustration within their lattices. Although there have been extensive studies of frustrated magnetism in pyrochlores, there has been little work on their frustrated magnetic states in the presence of mobile charge carriers. Relatively few metallic pyrochlores have been reported, despite the fact that exotic electronic states in doped frustrated magnets have been predicted. In this work, we employ density functional theory calculations to investigate anion doping in titanate and vanadate pyrochlores by substituting one oxygen atom with N^3- and F⁻ anions. One of the distinctive features of pyrochlores is the presence of two distinct oxygen sites, furthermore, chemical substitution on these sites does not disturb the magnetic lattice. We investigate changes to the structural and electronic properties with anion substitution and employ transition level diagrams to determine the position of defect states with respect to the bandgap. Our findings provide insight into how anion substitution can influence the electronic properties of pyrochlore oxides and offer potential pathways to achieving enhanced conductivity in these materials.