Resonance Raman scattering in Ti2O3 in the range 1.8–2.7 eV

Shin, Sungwon; Pollak, Fred H.; Halpern, T.; Raccah, P. M.

doi:10.1016/0038-1098(75)90453-6

Cited by 25 publications

(10 citation statements)

References 7 publications

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“…All are shifted towards the lower wavenumbers compared to the bulk: 210, 256, 298, 339, 449, 503, and 559 cm -1 instead of 237.5, 279, 306, 350, 466, 514, and 571 cm -1 . Moreover, the intensities of the first A 1g and the first E g lines are almost the same, while in bulk samples, and 632.8 nm excitation wavelength, the first A 1g mode was previously reported to be about five times stronger than the first E g mode [24]. Such redshift and change in relative intensities can also be observed during the heating of the bulk crystal above the metal-insulator transition temperature.…”

Section: Resultssupporting

confidence: 51%

Suppression of the metal-insulator transition in magnetron sputtered Ti2O3 films

et al. 2020

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We report on the synthesis of titanium suboxide films using a magnetron sputtering setup. The structure of the produced films is characterized using Raman spectroscopy and X-ray diffraction and electrical properties are measured by four-probe method. We demonstrate that depending on the oxidation rate of the growing films it is possible to produce polycrystalline α-TiO, corundum and orthorhombic Ti 2 O 3 or almost amorphous TiO 2 . We focus on the characterization of the two phases of Ti 2 O 3 and show that their structure and electrical properties significantly differ from earlier results obtained for bulk crystals or epitaxial films. Our corundum-type Ti 2 O 3 films have high electrical conductivity (compared to the bulk) and no metal-insulator phase transition: the material is locked in the metallic state. The conductivity of our orthorhombic Ti 2 O 3 is lower compared to epitaxial films; this phase does not demonstrate any phase transitions as well. IntroductionThe first report on titanium sesquioxide (titanium III oxide, or Ti 2 O 3 ) crystal structure was published more than 90 years ago [1]. This material normally crystallizes into corundum-type space group R c with lattice parameters of a = 5.157 Å and c = 13.61 Å. Ti 2 O 3 attracted some interest due to a broad semiconductor to metal phase transition in the temperature range of 150-300 °C [2, 3]. This transition is accompanied by a rapid change of physical properties such as electrical resistivity [4], specific heat [5], elastic constants [6], and magnetic susceptibility [7]. Very recently it was shown that nanoparticle-based Ti 2 O 3 films could be used as an efficient photothermal material promising for seawater desalination and purification [8]. Under high pressures and high temperatures (19 GPa and 1850 K) corundum Ti 2 O 3 phase transforms into golden semiconducting Th 2 S 3 -type structure, which is fully quenchable to ambient conditions (Pnma orthorhombic cell, a = 7.82 Å, b = 2.85 Å, c = 8.12 Å at ambient conditions) [9, 10].Recently, it was shown that Ti 2 O 3 could crystallize into another space group, Immm, with orthorhombic cell parameters of a = 9.39 Å, b = 4.42 Å and c = 2.81 Å. The material was obtained as an epitaxial thin film on (0001) sapphire substrate using pulsed laser deposition and Ti 2 O 3 target at substrate temperatures above 700 °C [11]. Such films are ferromagnetic n-type semiconductors with a very high electron concentration and they also demonstrate a semiconductor to metal transition at about 370 K. The synthesis of the same material by cathodic arc sputtering was reported in our previous article, but that time the phase was not properly identified and characterized [12].In most studies, titanium suboxides are produced by different chemical methods, including carbothermic [13], metallothermic [14] or hydrogen [15] reduction of TiO 2 or by oxidizing different titanium-containing precursors, such as TiCl 3 [16], TiH 2 [17], titanium-tetraisopropoxide [18], and others. These methods usually lead to the formation of the bulk o...

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Section: Resultssupporting

confidence: 51%

Suppression of the metal-insulator transition in magnetron sputtered Ti2O3 films

et al. 2020

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“…Figure 1 shows the Raman spectra of the high-temperature-Ti 2 O 3 (HT-Ti 2 O 3 ) and low-temperature-Ti 2 O 3 (LT-Ti 2 O 3 ) films. The Raman spectrum of the HT-Ti 2 O 3 film recorded using a He-Ne laser shows seven peaks, which is consistent with previous reports [11][12][13]24,25 . In corundum-type crystal structures, two A 1g and five E g modes are Raman active following the symmetry considerations 28 .…”

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confidence: 91%

Metallic ground states of undoped Ti2O3 films induced by elongated c-axis lattice constant

Yoshimatsu

Hasegawa

Nambu

et al. 2020

Sci Rep

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Ti2O3 exhibits unique metal–insulator transition (MIT) at ~ 450 K over a wide temperature range of ~ 150 K. The close relationship between MIT and crystal deformation has been proposed. However, as physical properties are governed by the thermodynamic equilibrium in bulk systems, conducting experimental studies under different lattice deformations remains challenging. Epitaxial thin films can offer high flexibility to accommodate adaptive crystal lattices and provide efficient platforms for investigating the MIT. In this study, we report the synthesis of corundum-type Ti2O3 films on various growth temperatures. We found that the metallic ground states appeared in the films grown at low temperatures. The electronic ground states were further investigated by the electronic-structure calculations. Results suggest that the electrical properties of Ti2O3 films were governed by the c/a ratio of the crystal structure, and the absence of the MIT was attributed to the lattice deformation characterized by an elongated c lattice constant.

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“…It is also noted that the mixed phase of anatase TiO 2 , oxygen vacancy defect and the Ti 3+ interstitial defects in the outside surface of H:TiO 2 NFs has broaden peaks with respect to pristine TiO 2 NFs as shown in Fig. 4(b)5051 TEM microstructure analysis and the TERS reveals that H:TiO 2 NFs contains a highly crystalline anatase TiO 2 core and a hydrogenated TiO 2 shell.…”

Section: Resultsmentioning

confidence: 90%

Improved Solar-Driven Photocatalytic Performance of Highly Crystalline Hydrogenated TiO2 Nanofibers with Core-Shell Structure

Chen

Huang

et al. 2017

Sci Rep

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Hydrogenated titanium dioxide has attracted intensive research interests in pollutant removal applications due to its high photocatalytic activity. Herein, we demonstrate hydrogenated TiO2 nanofibers (H:TiO2 NFs) with a core-shell structure prepared by the hydrothermal synthesis and subsequent heat treatment in hydrogen flow. H:TiO2 NFs has excellent solar light absorption and photogenerated charge formation behavior as confirmed by optical absorbance, photo-Kelvin force probe microscopy and photoinduced charge carrier dynamics analyses. Photodegradation of various organic dyes such as methyl orange, rhodamine 6G and brilliant green is shown to take place with significantly higher rates on our novel catalyst than on pristine TiO2 nanofibers and commercial nanoparticle based photocatalytic materials, which is attributed to surface defects (oxygen vacancy and Ti3+ interstitial defect) on the hydrogen treated surface. We propose three properties/mechanisms responsible for the enhanced photocatalytic activity, which are: (1) improved absorbance allowing for increased exciton generation, (2) highly crystalline anatase TiO2 that promotes fast charge transport rate, and (3) decreased charge recombination caused by the nanoscopic Schottky junctions at the interface of pristine core and hydrogenated shell thus promoting long-life surface charges. The developed H:TiO2 NFs can be helpful for future high performance photocatalysts in environmental applications.

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Resonance Raman scattering in Ti2O3 in the range 1.8–2.7 eV

Cited by 25 publications

References 7 publications

Suppression of the metal-insulator transition in magnetron sputtered Ti2O3 films

Suppression of the metal-insulator transition in magnetron sputtered Ti2O3 films

Metallic ground states of undoped Ti2O3 films induced by elongated c-axis lattice constant

Improved Solar-Driven Photocatalytic Performance of Highly Crystalline Hydrogenated TiO2 Nanofibers with Core-Shell Structure

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