The interplay between the electronic properties and atoms of a crystal is the origin of many fascinating phenomena such as superconductivity. Physicists from the RIKEN Advanced Science Institute, Wako, the University of Tokyo and Osaka University have now discovered another intriguing phenomenon in the newly synthesized oxide compound LiRh2O4, which could lead to a more efficient generation of electricity from heat.
LiRh2O4 belongs to one of the most common families of oxides, the spinels. Spinels are an attractive playground for physicists: the unique geometry of their atomic lattice can make a mutually convenient arrangement of electrons and ions difficult. At room temperature, the rhodium ions in LiRh2O4 are forced to assume a state of mixed valency, Rh3.5+, whereas the electrons are distributed indiscriminately between the different orbital electronic states.
Led by Hidenori Takagi, the researchers studied how this uneasy arrangement in LiRh2O4 plays out at lower temperatures1, and they have discovered several electronic and structural rearrangements occurring at different temperatures. At 230 K (-43.15 °C), the crystal suddenly expands in one direction and contracts in another, a structural change attributed to the ‘Jahn-Teller effect’. A common occurrence in oxides, this effect explains how the crystal distorts itself to gain energy by lifting the equivalence between the different orbital electronic states, in this case favoring the yz and zx orbitals over the xy ones.
Surprisingly, at the temperature of 170 K (-103.15 °C) the electrical resistivity suddenly increases, and the material changes from a metal to an insulator. This transition indicates that the Rh3.5+ ions have separated into Rh3+ and Rh4+ ions. Intriguingly, it is the Jahn-Teller effect that dictates this transition because it is the electrons from the Rh4+ ions occupying the xy orbitals that are exposed by the crystal distortion. “The Jahn-Teller effect really is the master of the physics here,” notes Takagi.
The implications of this discovery may extend well beyond the interest of physicists because, owing to the indiscriminateness of electrons, the thermoelectric power of LiRh2O4 is enhanced dramatically when the Jahn-Teller effects are about to occur. A large figure for thermoelectric power is the key to efficient generation of electricity from heat. “Our study provides an important clue for the exploration of high-performance thermoelectrics and therefore bridges basic and applied physics,” says Takagi. The restructuring seen in this spinel compound may well prove an important template for more efficient electricity generation.
1. Okamoto, Y., Niitaka, S., Uchida, M., Waki, T., Takigawa, M., Nakatsu, Y. , Sekiyama, A., Suga, S., Arita, R. & Takagi, H. Band Jahn-Teller instability and formation of valence bond solid in a mxed-valent spinel oxide LiRh2O4. Physical Review Letters 101, 086404 (2008).
The corresponding author for this highlight is based at the RIKEN Magnetic Materials Laboratory
Supersonic waves may help electronics beat the heat
18.05.2018 | DOE/Oak Ridge National Laboratory
Researchers control the properties of graphene transistors using pressure
17.05.2018 | Columbia University
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.
The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
23.05.2018 | Life Sciences
23.05.2018 | Life Sciences
23.05.2018 | Physics and Astronomy