Ultrathin Titanium Oxides Show Superconductivity

Researchers in Japan have created higher titanium oxide films that behave like superconductors.

AsianScientist (Oct. 11, 2017) – In a study published in the journal Scientific Reports, scientists in Japan have reported superconductivity in ultrathin films of higher titanium oxides.

Titanium dioxide (TiO2) is commonly used as a whitener in sunscreens and paints such as the white lines seen on tennis courts. Less well known are other higher titanium oxides—those with a higher number of titanium and oxygen atoms than TiO2—that are now the subject of intensifying research due to their potential use in next-generation electronic devices.

In this study, researchers at the Tokyo Institute of Technology have reported superconductivity in two kinds of higher titanium oxides prepared in the form of ultrathin films. The thin films are epitaxial, meaning that they have a well-aligned crystalline structure. With a thickness of around 120 nanometers, these materials possess novel properties that warrant further investigation.

To create the films, the researchers used Ti2O3 as the starting material. Then, under precisely controlled atmospheric conditions, the Ti4O7 and γ-Ti3O5 films were grown layer by layer upon sapphire substrates in a process called pulsed-laser deposition. To verify the crystalline structures of the films, the team collaborated with researchers at the National Institute for Materials Science in Japan who characterized the films with techniques such as X-ray diffraction.

“We succeeded in growing thin films of Ti4O7 and γ-Ti3O5 for the first time,” said Assistant Professor Kohei Yoshimatsu, the lead author of the paper.

Until now, the two materials had only been studied in bulk form, in which they behave as insulators—the opposite of conductors. The formation of electrically conductive thin films is therefore seen as a big advance for fundamental physics.

The researchers found that the superconducting transition temperature reached 3.0 Kelvin (K) for Ti4O7 and 7.1 K for γ-Ti3O5. A superconducting transition temperature of 7.1 K is the highest known among oxides of titanium.

As yet, no one knows exactly how superconductivity arises in these titanium oxides. The irregular, or what is known as non-stoichiometric, arrangement of oxygen atoms is thought to play an important factor. This arrangement introduces oxygen vacancies that are not stable in bulk form. By creating just enough conductive electrons, the oxygen vacancies may help induce superconductivity.

Yoshimatsu noted that more work is needed to examine the underlying mechanisms of superconductivity in higher titanium oxide films. As these materials are cheap and relatively simple, made of only two kinds of elements, he added that they are attractive for further research.

He concluded that the study may advance the development of new kinds of electronic circuits and, ultimately, faster computers.


The article can be found at: Yoshimatsu et al. (2017) Superconductivity in Ti4O7 and γ-Ti3O5 Films.

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Source: Tokyo Institute of Technology; Photo: Shutterstock.
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