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
Did you know that the wrapping of Easter eggs benefits from specialty light sources?
13.04.2017 | Heraeus Noblelight GmbH
To e-, or not to e-, the question for the exotic 'Si-III' phase of silicon
05.04.2017 | Carnegie Institution for Science
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences