Studies of the Optical and Infrared Absorption Spectra of Rutile Single Crystals

Abstract

The optical absorption of single crystals of synthetic rutile was investigated in the spectral range 1200 to 25 000 cm⁻¹ from room temperature to 1000°C. The electronic absorption exhibits dichroic behavior. The edge moves toward lower energies as temperature is increased, with the shift depending upon the absorption coefficient; for a decadic absorption coefficient α′ of 400 cm⁻¹, the shift is −7.1×10⁻⁴ ev/°K, while at 1 cm⁻¹ it is −9.5×10⁻⁴ ev/°K. The broad band in the region of 6850 cm⁻¹ which occurs in reduced rutile does not appear in fully oxidized rutile, even at high temperatures. At high temperatures an additional wavelength‐independent absorption appears which can be correlated in good agreement with dc conductivity by applying the Drude‐Zener theory of free carrier absorption. New bands in the 3300 cm⁻¹ region are shown to stem from O–H valence vibrations. The main bands are unusually sharp, with peaks at 3277 and 3322 cm⁻¹ and half‐widths of 28 and 13 cm⁻¹. A satellite structure of combination and difference bands was also detected. Deuterium substitution produces an absorption band at 2442 cm⁻¹. The entire structure shows a marked dependence of the absorption on the polarization direction of the light. Some evidence is presented that these O–H groups cause a dielectric dispersion.