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

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.