The molecular structure of bismuth oxide by Raman spectroscopy

A new method is presented for interpreting the Raman spectra of bismuth oxides. The method relies on empirical relations between bismuth-oxygen (BiO) bond lengths, bond strengths, and Raman stretching frequencies. A least-squares exponential fit of crystallographically determined BiO bond lengths and Raman stretching frequencies is presented along with a relation between BiO bond strengths, in valence units, and Raman stretching frequencies. The empirical bond length/bond strength/Raman stretching frequency relationships lead to a unique and effective method of interpreting Raman spectra of bismuth oxide species. This method allows the systematic determination of the BiO bond lengths and oxygen coordination of a BiOx polyhedron from its Raman spectrum. The utility of the method is illustrated by estimating the Raman stretching frequencies for ideally symmetric bismuth oxide structures BiO4, BiO5, BiO6, BiO7, and BiO8. As a final, practical example the method is used to determine the bond lengths and coordinations of the bismuth oxide species in the β- and δ-phases of Bi2O3. This new approach for evaluating the Raman spectra of bismuth oxide species is expected to be generally applicable to all bismuth oxides, regardless of environment, physical state, or oxidation state.