Raman studies of the intermediate tin-oxide phase

The existence of an intermediate phase of tin oxide was first reported in 1882. However, its stoichiometry and its crystal structure have been dubious and heavily debated ever since, despite a multitude of structural investigations. We show that Raman spectroscopy combined with ab initio theory offers a viable alternative for structure determination in cases where diffraction studies are inconclusive. We unambiguously identify the intermediate phase as ${\mathrm{Sn}}_{3}{\mathrm{O}}_{4}$ and rule out the other likely candidate, ${\mathrm{Sn}}_{2}{\mathrm{O}}_{3}$. We assign the one-phonon Raman signals of ${\mathrm{Sn}}_{3}{\mathrm{O}}_{4}$ to the mode symmetries of the corresponding point group ${C}_{2h}$ and confirm that $P{2}_{1}/c$ with 14 atoms per unit cell is the space group of ${\mathrm{Sn}}_{3}{\mathrm{O}}_{4}$.