Small-polaron-induced infrared opacification in rutile TiO2

Abstract

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.

Investigation of the local photothermal effects by fabricating a CQDs/Au/TiO2 photoelectrode in a PEC water splitting system

“…The small polaron semiconductor characteristics of rutile TiO 2 may be one of the reasons. [33][34][35]…”

“…In this work, we selected rutile TiO 2 nanorod arrays with a high specific surface area as the substrate, taking into consideration that rutile TiO 2 can be as a small polaron semiconductor. [33][34][35] Then a CQDs/Au/TiO 2 composite photoanode was constructed by loading Au NPs and CQDs on the TiO 2 nanorod array. On the one hand, the optimal loading of Au NPs and CQDs was investigated, and the synergistic effect of Au NPs and CQDs on the photoelectrochemical performance was studied in detail.…”

The Role of Water Molecules on Polaron Behavior at Rutile (110) Surface: A Constrained Density Functional Theory Study

“…Rutile TiO 2 , a model photocatalytic material, has aroused extensive attention due to its low cost, high stability, and excellent reactivity. − The band gap of its bulk case is about 3.04 eV in the ultraviolet range. , It has been found that the light absorption and reactivity of rutile is strongly related to the excess electrons, which has been proved to be Holstein polarons. − Various kinds of factors greatly influence the formation of polaron including lattice defects (such as O v − or T int , ), atomic coordination, external doping, , crystal boundary effects, and processes of optical excitation. , Numerous scholarly works focus on investigating the polarons. − From the experimental side, Macdonald et al used electron paramagnetic resonance (EPR) to study photoexcited electrons in nanocrystalline rutile, and they found that an EPR signal appears after UV–visible light irradiation. The signal can even remain after turning off the irradiation, suggesting the stability of polarons.…”