Brillouin scattering of V2O5 and Sn-intercalated V2O5

The Brillouin scattering spectra of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{V}}₂{\mathrm{O}}₅$ and Sn-intercalated ${\mathrm{V}}₂{\mathrm{O}}₅$ (${\mathrm{Sn}}_0.07{\mathrm{V}}₂{\mathrm{O}}₅$) were measured for sound propagation directions at and near the [001] direction, which is normal to the van der Waals gaps in this layered material. Anisotropic sound velocities and stiffness tensor elements ${c}_ij$ were determined from the Brillouin frequency shifts. Measurements for propagation in the [001] direction in pure ${\mathrm{V}}₂{\mathrm{O}}₅$ yielded ${c}₃₃=42.20\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.38\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, ${c}₄₄=23.55\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.27\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, and ${c}₅₅=25.65\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.27\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ showing substantial disagreement with some published theoretical calculations. High longitudinal stiffness values $\ensuremath{\sim}230\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ in the [100] and [010] directions correspond to remarkably high longitudinal sound velocities of 8290 m/s, demonstrating strong anisotropy associated with the layered structure. ${\mathrm{Sn}}_0.07{\mathrm{V}}₂{\mathrm{O}}₅$ was found to have stiffnesses of ${c}₃₃=43.72\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.23\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, ${c}₄₄=22.91\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.20\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, and ${c}₅₅=26.54\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.22\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$, indicating that some deformation modes are slightly stiffened while others may be unaffected or even softened by the intercalant.