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Pressure-induced reentrant metallic phase in lithium (Press Release)

Release Date
23 Apr, 2014
  • BL10XU (High Pressure Research)

Osaka University
Japan Synchrotron Radiation Research Institute

 Collaborative research group of Osaka University and Japan Synchrotron Radiation Research Institute found that elemental metal lithium that transited to a semiconductor under high pressure of 80 GPa reverted back to a metal when it was compressed exceeding 120 GPa. This change is accompanied with a structural transition. Takahiro Matsuoka and Katsuya Shimizu from Research Center of Quantum Science and Technology under Extreme Conditions Osaka University performed X-ray diffraction measurements by using the synchrotron radiation from SPring-8*1 to investigate the structural transformations, and at the same time they monitored electrical properties changes of lithium by electrical resistance measurements. Their experiments also revealed that the re-entrant metallic phase of Li is a so-called bad metal with a large electrical resistivity on the other hand it exhibited a possible transition to a low-temperature phase that might be a superconductor.
 Because Li is a typical simple metallic element, it has been playing important roles in understanding the physical properties of general metals. It is expected that any materials becomes metallic at ultimately compressed conditions. The current experimental investigation added a new insight about materials. Materials can be either metallic or semiconductive depending on its density.
 The experimental observation of pressure-induced metal-semiconductor-metal transitions is expected to contribute to expanding our understandings about physical properties of metals.

Pressure-induced reentrant metallic phase in lithium
T. Matsuoka, M. Sakata, Y. Nakamoto, K. Takahama, K. Ichimaru, K. Mukai, K. Ohta, N. Hirao, Y. Ohishi, and K. Shimizu


Fig. 1		Schematic drawing of crystal structure of CmABCB1
Fig. 1 Diamond anvil cell.*3

Sample and electrodes are compressed together between a pair of diamond anvils. Electrical resistance and X-ray diffraction are monitored under high-pressure conditions.

Fig. 2 (Upper panels) Pressure (left) and temperature (right)
Fig. 2 (Upper panels) Pressure (left) and temperature (right)
(dependence of electrical resistivity of Li. lower panel) Temperature vs. Pressure phase diagram of Li.

The vertical broken lines are structural phase boundaries. Tc indicates superconducting transition temperature. Li is metallic at pressures below 80 GPa, and it is a semiconductor between 80 GPa and 120 GPa. At above 120 GPa, Li is a metal. Tx indicates the transition temperature to low-temperature phase that may be a superconductor. A red dashed line indicates the phase boundary obtained from pressure dependence of Tx.

*1 SPring-8

SPring-8 (Harima Science Park, Hyogo, Japan) is a synchrotron radiation facility that provides the world's highest brilliance radiation. It’s owned by Riken and run by JASRI. The name 'SPring-8' is from “Super Photon ring-8 GeV”. Synchrotron radiation is a electromagnetic wave radiated when charged particles are forced to bend in magnetic fields. Synchrotron radiation from SPring-8 is widely used for the studies of nano-technology, bio-technology and industrial purposes.

*2 Free electron model
Free electron model is one of the models to describe the electronic states of materials. This model assumes that a charged particle (electron) can move almost freely in materials (metals). Free electron model can successfully describe many of physical properties of general metals.

*3 Diamond Anvil Cell
Diamond anvil cell (DAC) is a device to generate high pressure. It consists of two tiny diamond chips. Opposing two diamond chips sandwich a sample and pressure transmitting medium that are contained in a gasket. High pressures exceeding 100 GPa can be generated when small diamond tip is employed. On the other hand, small diamond chips require small sample amount, and this makes physical properties measurements difficult. In order to perform X-ray diffraction and other experiments with high quality, the use of high-brilliance synchrotron radiation is necessary. This study had several technical difficulties peculiar to high-pressure experiments arising from small sample size. Researchers overcome problems by using beamtimes gave for SPring-8's long term program.

For more information, please contact:
  Prof. Takahiro Matsuoka (Gifu University)
    E-mail : mail1
  Prof. Katsuya Shimizu (Osaka University)
    E-mail : mail2