DFT‐aided interpretation of the Raman spectra of the polymorphic forms of Y₂Si₂O₇

Y 2 Si 2 O 7 is an intriguing material combining a complex structural polymorphism with several important technological applications. Raman spectra were experimentally determined for most of the seven known modifications of Y 2 Si 2 O 7 except the form ε, and in the case of β, γ, δ and ζ for the first time. The error‐prone procedure of mode assignment to the measured Raman bands, usually done by comparison with similar or related structures, has been replaced by quantum chemical calculations of the spectra of the polymorphs. Various functionals were evaluated considering the agreement of the calculated modes with the experimental data. The average and maximum deviations between calculated and experimental spectra are ± 8 cm −1 and 20 cm −1 , respectively. Assignments of most of the observed bands to vibrational modes are given. The relationship between selected Raman bands, SiO and YO polyhedra stretching and bending modes, and the crystal structures are discussed. Y 2 Si 2 O 7 offers the possibility to study the relationship between structural and spectral changes in a chemically fixed system.