The influence of sulfur substitution on the atomic displacement in Bi2Ti2O7

To clarify the role of A2O′ and B2O6 networks on cation displacement observed in Bi2Ti2O′O6, we used density functional theory calculations to examine the effect of sulfur substitution on the O′ and O sites on lone pair formation and resulting atomic displacement observed in Bi2Ti2O′O6. Cation displacement in bismuth titanate is suppressed only when S is substituted on the O′ site. Analysis of the electronic structure shows that S substitution on the O′ site suppresses the formation of the asymmetric p-type lone pair by modifying the Bi-anion hybridization. Lone pair formation is favored in Bi2Ti2O′S6 and the atomic displacement is larger than that observed in Bi2Ti2O′O6. This enhanced displacement is due to weaker Bi–S versus Bi–O interactions leading to significantly stronger hybridization between the Bi and O′ states in Bi2Ti2O′S6. We also induced lone pair formation in a metallic bismuth pyrochlore oxide (Bi2Ru2O′O6) by modifying the Bi–O interactions through S substitution on the B2O6 network, indicating atomic displacement on the A2O′ network may be achieved by modifying the B2O6 network.

Graphical abstractThe electron localization function for Bi2Ti2O6O′ and Bi2Ti2O6S′ respectively show that sulfur substitution on the O′ site will suppress lone pair formation.Figure optionsDownload full-size imageDownload as PowerPoint slide