Spontaneous Raman scattering of Lu$_2$Si$_2$O$_7$ single crystals at temperatures in the range from 20 to 2173 K

Detailed studies of the polarized Raman spectra of lutetium pyrosilicate single crystals have been performed in a wide temperature range from 20 to 1500 K. This has made it possible for the first time to identify the entire set and symmetry of the internal vibrations of the [Si$_2$O$_7$]$^{6-}$ anion and the lattice vibrations of this compound. The Raman spectra of the lutetium pyrosilicate have been investigated in the temperature ranges preceding the melting, the molten state, and the overheated melt of the compound up to 2173 K. The Raman spectra of lutetium pyrosilicate single-crystal microregions have been studied in order to elucidate the nature of defect inclusions in their bulk.