Exploring novel functional properties arose from anion order in mixed anion compounds

Abstract

Studies on mixed anion compounds require determination of its anion order. The characteristics of mixed anion compounds vary depending on presence of anion order. Here, we found that application of the steric effect arose from 6s² lone pair electrons of Pb²⁺ induces O/F anion order in oxyfluorides. Functional properties such as a high dielectric constant and visible light photocatalysis were found in the Pb-containing oxyfluorides. These properties are strongly correlated with the O/F anion order. On the other hand, when O/F anion order is absent, mixing anion just act as electron doping on cations. Electron doping induced by mixing O²⁻ and F⁻ led a colossal negative thermal expansion in PbVO_3−xF_x oxyfluoride. Material design based on O/F anion order is promising for the development of applications of ceramics materials.