The Unexpected Role of Fluorine in the Band Gap Narrowing of Silver Niobium and Tantalum Pyrochlore Oxyfluorides
Year: 2025
Type: article
Abstract: Mixed anion compounds have attracted growing interest in solid-state chemistry as a way to tailor physical properties. In this work, we synthesized new silver niobium and tantalum pyrochlore oxyfluorides by an ion-exchange reaction from Na 2 M 2 O 5 F 2 ( M = Nb or Ta). Instead of a classical Na + /Ag + cation exchange, a less conventional dual cation and anion exchange reaction (2 Na + + F – )/(Ag + + H 2 O) takes place. Indeed, chemical and thermal analyses, as well as Rietveld refinement and 19 F NMR, reveal the formation of AgTa 2 O 5 F·H 2 O and Na 0.4 Ag 0.8 Nb 2 O 5 F 1.2 ·0.8H 2 O leading to a significant band gap narrowing of approximately 0.4 eV, as determined by diffuse reflectance spectroscopy. DFT calculations show that Ag 4d–O 2p states are located at the edge of the valence band and that the presence of fluorine in the coordination sphere of Ag promotes the hybridization and hence contributes to the band gap narrowing.
Source: Inorganic Chemistry
Institutions: Centre National de la Recherche Scientifique, École Nationale Supérieure de Chimie de Lille, Université de Lille, Unité de Catalyse et Chimie du Solide, Centrale Lille Institut, Institut Universitaire de France, Delft University of Technology, Institut des Matériaux Jean Rouxel, Nantes Université, Le Mans Université, Institut des Molécules et Matériaux du Mans
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4407766895