Band Gap Tuning in Bismuth Oxide Carbodiimide Bi₂O₂NCN

Layered bismuth oxides exhibit a broad range of tunable physical properties as a result of their excellent structural versatility which facilitates compositional substitutions at both cationic and anionic positions. Here we expand this family in a new direction through the preparation of the first example of a bismuth-containing oxide carbodiimide, Bi₂O₂NCN, which assumes an extended variant of the anti-ThCr₂Si₂ structure-type adopted by Bi₂O₂ Ch ( Ch = Se or Te) oxide chalcogenides. Electronic structure calculations reveal the title compound to be an indirect band gap semiconductor with a band gap of approximately 1.4 eV, in good agreement with the measured value of 1.8 eV, and intermediate between that of structurally related Bi₂O₂S (1.12 eV) and β-Bi₂O₃ (2.48 eV). Mott-Schottky experiments demonstrate Bi₂O₂NCN to be an n-type semiconductor with a conduction band edge position of -0.37 V vs reversible hydrogen electrode. This study highlights the pseudochalcogenide nature of the ^-N═C═N^- carbodiimide anion, which may be substituted in place of oxide or chalcogenide anions in this and potentially other structural classes as an effective means of electronic tuning.