Infrared and Raman spectra of Bi 2 O 2 X and Bi 2 OX 2 (X = S, Se, and Te) studied from first principles calculations.

The bismuth oxychalcogenide compounds contain many different kinds of materials, such as Bi 2 O 2 X and Bi 2 OX 2 (X = S, Se, and Te). These materials have different but similar layered crystal structures and exhibit various interesting physical properties. Here, we have theoretically investigated their Raman and infrared spectra by first principles calculations based on density functional theory. It is found that in Bi 2 O 2 Se the calculated frequency of the A 1g Raman active mode is in good agreement with the experimental measurements while the other three modes are ambiguous or not observed yet. The Raman and infrared spectra of other materials are also presented and need further confirmation. Our work provides the structural fingerprints of these materials, which could be helpful in identifying the crystal structures in future experiments.