Oxides of transition metals such as titanium are of interest for applications, such as hydrogen gas sensors or as catalysts, and have intriguing fundamental physical properties. In particular, the origin of an intermediate temperature phase of the compound Ti4O7 has puzzled scientists for decades.
By studying the different electrical phases of Ti4O7, researchers from the RIKEN SPring-8 Center in Harima, along with colleagues from other institutions in Japan, have now taken important steps towards understanding the fundamental differences between the compound’s electrical conductivity at room and low temperatures, and the enigmatic phase that forms at intermediate temperatures.
At room temperature and down to temperatures of 154 K, Ti4O7 is an excellent conductor, as it allows fast transport of electrical charges. At temperatures below 142 K, the compound is an electrical insulator. Between 142 K and 154 K, however, the mysterious intermediate temperature phase sets in where the compound is semiconducting. Both, the metallic and the insulating phases are well understood by classical theories. The semiconducting phase, however, is very strange and complex; its origin is particularly interesting because it is sandwiched by two such well-known phases, explains Munetaka Taguchi from the research team.
To elucidate the origin of the semiconducting phase, the researchers studied the electronic phases at the top of the valence band and bottom of the conduction band that are responsible for the electrical conduction. They employed the techniques of electron photoemission and x-ray absorption, which combined provide a detailed picture of the electronic phases.
In the high-temperature phase, Taguchi and colleagues found that so-called ‘coherent valence electrons’ extended as far as the conduction band, making it a metallic conductor. In the insulating phase, there is a gap in the electronic band structure and no electrons are available in the conduction band. For the intermediate regime, however, a small number of coherent electronic phases remain close to the conduction band and explain the measured electrical conductivity.
While it is clear that the small number of coherent electrons is a remnant of the metallic phase, the transformation path—from the semiconducting state to both the room-temperature metal and the low-temperature insulating phase—remains unclear, notes Taguchi. With such crucial fundamental questions still unsolved, more work is needed to study the nature of the coherent electronic phases, which Taguchi hopes “will provide us [with] vital clues to a more complete understanding of phase transitions.”
The corresponding author for this highlight is based at the Excitation Order Research Team, RIKEN SPring-8 Center
1. Taguchi, M., Chainan, A., Matsunami, M., Eguchi, R., Takata, Y., Yabashi, M., Tamasaku, K., Nihino, Y., Ishikawa, T., Tsuda, S. et al. Anomalous state sandwiched between fermi liquid and charge ordered Mott-insulating phases of Ti4O7. Physical Review Letters 104, 106401 (2010)
gro-pr | Research asia research news
Researchers use light to remotely control curvature of plastics
23.03.2017 | North Carolina State University
TU Graz researchers show that enzyme function inhibits battery ageing
21.03.2017 | Technische Universität Graz
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy