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

Abstract

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.

Enhancement and Inversion of Absorptive Nonlinearity Induced by Topochemically Controlled Insulator-to-Metal Transition

“…Further increase of the oxygen deficiency results in the collapse of the anatase structure and the formation of Magnéli phases Ti 4 O 7 and then Ti 2 O 3 , where the bandgap is completely closed and the Fermi level enters into the conduction band (CB) crossed by Ti-d and O-2p orbitals. Previous experimental and theoretical reports have also revealed the presence of a metallic ground state for the Ti-suboxides. , For the nanoscale metallic Magnéli phases, the NLO absorption in the 1.0 μm region could be dominated by intraband transition and can be induced by depletion of energy states associated with Ti-2p orbitals in the metallic Ti suboxide like Ti 4 O 7 and Ti 2 O 3 , as shown in schematic illustration in Figure c,d. The origin of the NLO response manifested as SA in these metallic oxide NPs is mechanistically associated with the ultrafast thermalization and cooling of hot electrons that have been observed for noble metal-based systems. , …”

Photothermal conversion of Ti2O3 film for tuning terahertz waves

“…Figure 3C shows the square resistance of Ti 2 O 3 film against temperature from 25 C to 200 C. As can be seen, when the temperature increased from 25 C to 200 C, the square resistance of the Ti 2 O 3 thin film decreased from 390.2 U/, to 86 U/,. Alternatively, the square resistance increased from 85.9 U/, to 391.4 U/, with a temperature reduction from 200 C to 25 C. In this case, the temperature-dependent resistivity characteristic indicates the thermal-induced MIT of the Ti 2 O 3 film, and the change of resistivity can be attributed to the change in electronic structure of Ti 2 O 3 caused by temperature-induced lattice deformation (Honig, 1968;Vanzandtet al, 1968;Yoshimatsu et al, 2020). Notably, the resistance change curves during heating and cooling almost coincide, indicating that there is no hysteresis during the metal-insulator transition.…”

Recent Progress on Titanium Sesquioxide: Fabrication, Properties, and Applications

“…[22,57,58] Hence, α-Ti 2 O 3 nanoparticles, with sizes of tens or hundreds of nanometers, can be prepared from the reduction of TiO 2 nanoparticles [45] or ball milling bulk α-Ti 2 O 3 samples. [43,44,51,52] As for the epitaxial Ti 2 O 3 films, several filmgrowth techniques have been used to prepare the samples, including pulsed laser deposition (PLD), [46,49,59] and magnetron sputtering. [60,61] By using epitaxial stabilization, the metastable phases o-Ti 2 O 3 and γ-Ti 2 O 3 , not found in the bulk, can be artificially fabricated as thin films.…”

“…Fortunately, self‐doped α‐Ti 2 O 3 with Ti 4+ results in a larger bandgap [ 33 ] and could thus be a promising candidate for photocatalytic applications. On the other hand, V‐doping [ 31 ] or strain [ 47,59 ] can close its bandgap and enhance its conductivity, which could further improve its electrocatalytic efficiencies. Nevertheless, widely tuning its bandgap or achieving much larger bandgaps in α‐Ti 2 O 3 is still challenging. 3)Ti 2 O 3 ‐based heterostructures or composites could be good platforms to achieve novel functionalities in ways that single phase of Ti 2 O 3 cannot.…”