Ultrahigh-pressure fabrication of single-phase α-PbO2-type TiO2 epitaxial thin films

Abstract

Materials that are thermodynamically stable at ultrahigh pressures (>10 GPa) often exhibit unique physical properties. However, few studies have addressed the fabrication of epitaxial thin films of ultrahigh-pressure phases. Herein, we combine epitaxial thin film growth techniques with ultrahigh-pressure synthetic methods. We demonstrate the synthesis of single-phase epitaxial thin films of an ultrahigh-pressure polymorph of TiO2, α-PbO2-type TiO2. A rutile TiO2(100) epitaxial thin film is used as a precursor, and a structural phase transition is induced at 8 GPa and 800–1000 °C. This study demonstrates a new synthetic route to obtain ultrahigh-pressure-phase materials. The fabrication of epitaxial thin film ultrahigh-pressure phases paves the way for investigating the physical properties that arise at surfaces and interfaces of materials.

Impact of Surface Roughness on Recrystallization of an α-Al2O3(001) Single Crystal to α-AlO(OH) Diaspore Microcrystals

“…In conclusion, we investigate the topotaxial surface recrystallization of α-AlO(OH) diaspore on an α-Al ■ METHODS α-AlO(OH) diaspore microcrystals were synthesized via topotaxial surface recrystallization using a Kawai-type multianvil high-pressure apparatus 8 (Max Voggenreiter GmbH LPR 1000-400/50). The starting material was an α-Al 2 O 3 (001) single-crystalline substrate (Shinkosha, 5 mm in diameter and 0.5 mm in thickness); no precursor layer was formed on the surface.…”

“…It is crucial to investigate oriented crystals to gain insight into anisotropic physical and chemical properties of materials. We recently developed a technique for the application of ultrahigh pressure to thin films deposited on single crystals, aiming to prepare epitaxial thin films of ultrahigh-pressure-phase materials . Using this technique, it is possible to perform ultrahigh-pressure treatment (8 GPa) on a large-size single crystal with a diameter of 5 mm.…”

“…Using this technique, it is possible to perform ultrahigh-pressure treatment (8 GPa) on a large-size single crystal with a diameter of 5 mm. Thus, we performed ultrahigh-pressure treatments on rutile TiO 2 epitaxial thin films and demonstrated the growth of α-PbO 2 -type TiO 2 epitaxial thin films . We, therefore, expect that this technique, that is, the ultrahigh-pressure treatment of a large-size single crystal, could be applied for the investigation of the recrystallization of oriented α-AlO­(OH); only the recrystallization to α-AlO­(OH) using powders of α-Al 2 O 3 has been reported…”

“…We recently developed a technique for the application of ultrahigh pressure to thin films deposited on single crystals, aiming to prepare epitaxial thin films of ultrahigh-pressurephase materials. 8 Using this technique, it is possible to perform ultrahigh-pressure treatment (8 GPa) on a large-size single crystal with a diameter of 5 mm. Thus, we performed ultrahigh-pressure treatments on rutile TiO 2 epitaxial thin films and demonstrated the growth of α-PbO 2 -type TiO 2 epitaxial thin films.…”

“…Thus, we performed ultrahigh-pressure treatments on rutile TiO 2 epitaxial thin films and demonstrated the growth of α-PbO 2 -type TiO 2 epitaxial thin films. 8 We, therefore, expect that this technique, that is, the ultrahigh-pressure treatment of a large-size single crystal, could be applied for the investigation of the recrystallization of oriented α-AlO(OH); only the recrystallization to α-AlO(OH) using powders of α-Al 2 O 3 has been reported. 9 We herein report our investigation into the surface recrystallization of α-AlO(OH) microcrystals on an α-Al 2 O 3 (001) single-crystalline substrate.…”