Pressure and Temperature Dependences of the Raman-Active Phonons in SnO2

The temperature (10-500 °K) and pressure (0-4 kbar) dependences of the four Raman-active phonons $B_{1g}$, $E_g$, $A_{1g}$, and $B_{2g}$ as well as thermal expansion (93-700 °K) and isothermal compressibility (0-3 kbar) in Sn${\mathrm{O}}_2$ were measured. These measurements allowed us to determine the mode Grüneisen parameters for the Raman-active phonons and to separate the isobaric temperature dependence of each frequency into pure-volume and pure-temperature contributions. By this procedure the cubic and quartic anharmonicities responsible for the pure-temperature contributions to the mode frequencies were determined. The $B_{1g}$ mode in Sn${\mathrm{O}}_2$ exhibited anomalous temperature and pressure dependences in that $\omega \left(B_{1g}\right)$ increased with temperature and decreased with pressure. The remaining modes exhibited decreases in frequency with increasing temperature and increases in frequency with increasing pressure, characteristic of ionic crystals. The results are compared with the recent results on the isomorphic compound tetragonal Ti${\mathrm{O}}_2$.