Wavenumber (cm−1)

FT-IR assignment

500 cm −1

Stretching vibrations of Bi-O bonds in strongly distorted BiO6 octahedral units, B-O-B bond bending vibrations.

720 cm −1

Symmetric stretching vibrations of Bi-O bonds in pyramidal BiO3 units, O3B-O-BO3 bending vibrations.

840 cm −1

Symmetric stretching vibrations of Bi-O bonds in pyramidal BiO3 units, stretching vibrations of B-O bonds in BO4 units from diborate groups.

990 - 1080 cm−1

Stretching vibrations of B-Q bonds in BQ4 units from tri-, tetra-, and penta-borate groups.

1200 cm −1

Stretching vibrations of B-O bonds in BO3 units from meta- and ortho-borate groups.

1300 - 1500 cm−1

Asymmetric stretching vibrations of B-O bonds in BO3 and BQ2O units.