Small-polaron-induced infrared opacification in rutile TiO2

The infrared emittance of single-crystal rutile TiO2 has been measured from room temperature to 2000 K in dry air for two polarization states. A very strong thermally induced opacification phenomenon has been found, with the sample being completely opaque in the near-infrared range several hundred K before its melting point. A large contribution from small-polaron hopping conduction can explain this anomalous degree of opacification, much stronger than similar phenomena present in other octahedrally coordinated oxide materials. These quasiparticles manifest in the high-temperature optical conductivity as a thermally activated contribution, with an activation energy close to that of DC conductivity. The small-polaron nature of this phenomenon is strengthened by the observation of broad near-infrared bands. Published under an exclusive license by AIP Publishing.

Automated summary

The infrared emittance of single-crystal rutile TiO2 has been measured up to 2000 K in dry air, revealing a strong thermally-induced opacification phenomenon. This can be explained by small-polaron hopping conduction and is much stronger compared to similar phenomena in other oxide materials. The high-temperature optical conductivity shows a thermally activated contribution, with characteristics of small-polarons reinforced by the observation of broad near-infrared bands.