The high-pressure behavior of ${\mathrm{SnO}}_2$ has been examined by Brillouin and Raman scattering spectroscopy to pressures of 30 GPa at ambient temperature. The elastic constants $c_{11},$ $c_{12},$ $c_{44},$ and $c_{66}$ of rutile-type ${\mathrm{SnO}}_2$ were determined as a function of pressure to 13 GPa by Brillouin spectroscopy and the Raman-active modes have been measured up to 30 GPa. The transition from the rutile- to the ${\mathrm{CaCl}}_2$-type structure was observed. The Raman-active soft mode and the elastic soft mode behavior were fit to an order parameter model with bilinear coupling of the Raman-active order parameter and the elastic strain. It is shown that the pressure dependence of the Raman-active soft mode is controlled in part by the characteristic frequencies of the two coupled soft modes. No further indications for soft-mode-driven phase transitions at higher pressures were found.

• Received 23 August 2002

DOI:https://doi.org/10.1103/PhysRevB.67.174110