Infrared Absorption in Single-Crystal Stannic Oxide: Optical Lattice-Vibration Modes

Abstract

The ir reflection spectrum of single‐crystal stannic oxide has been observed at room temperature in the region 2000 to 100 cm⁻¹, and analyzed by classical dispersion theory to give values for the transverse and longitudinal optical‐mode frequencies. For the cassiterite structure, four lattice‐vibration modes may interact with infrared radiation, three of these with radiation polarized perpendicular to the c axis, and the remaining one with radiation polarized parallel to the c axis. The oscillator frequencies found for the best fit to the experimental reflection curves are: $\mathrm{E\perp c}$ , 243, 284, and 605 cm⁻¹; E ∥ c, 465 cm⁻¹. Low‐frequency dielectric constants are estimated from this analysis to be 13.5 and 9.58 for $\mathrm{E\perp c}$ and E ∥ c, respectively, which are about half the literature values. The $\mathrm{E\perp c}$ value was confirmed directly in a substitution bridge measurement yielding 15±1 for the frequency range 10² to 10⁶ Hz.