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Attraction of material science of ultra-high pressure and ultra-high temperature
World of ultra-high pressure over 10,000 atmosphere
The world where we live has 1 atmosphere. We probably cannot imagine the pressure of more than 10,000 atmosphere (about 1GPa: Giga Pascal). The deepest place at the bottom of the ocean is about 0.1 GPa. You can imagine a little bit how high the pressure over 1 Gpa is. However, in space the world of super ultra-high pressure over 100 GPa is not even rare. The center of the earth is about 360 GPa. What can we make if we synthesize the substance in the world of such ultra-high pressure? This simple question opens the door to this mysterious world.
Material creation under ultra-high pressure and ultra-high temperature
The temperature and the pressure are the important thermodynamic variables to control phase stability. Raising those up to super-high level, phase stability can change dramatically. We are trying to create the new materials with our original device to generate ultra-high pressure and ultra-high temperature, which could not be made at the usual temperature. The three states of the materials are solid, fluid, gas. Under the ultra-high pressure and temperature, the materials enter a complicated state. For example, the unusual state called supercritical fluid, which is not classified as solid or fluid, appears and we are able to reach the area of chemical reaction. The regular chemical reaction of supercritical fluid happens in the pressure area of MPa order, but we are trying to create materials utilizing supercritical fluid under ultra-high pressure and temperature of tens of GPa and thousands of K. We can get good crystalline development in a short time by utilizing high reactive supercritical fluid. We have been successful in synthesizing novel metal nitride full of nitrogen by reacting supercritical nitrogen fluid under super high pressure and temperature and various transition metals and rare earth metals.
Not only synthesis reaction, we are attempting single crystal growth under super high pressure and super high temperatures. We have been successful in making unique crystal in submicron size. For instance, in the single crystal growth method, using the supercritical nitrogen fluid the single the single crystal of gallium nitride (GaN), which is used as semiconductor material of blue light emitting diode, grows in short time. Recently we found that the unique crystal called hollow prism in submicron size grows by doing solution growth for Titanium oxide (TiO2), which is semiconductor material used for photocatalyst for a few seconds under super high pressure and temperature. [See the details in the research achievements]
How do we generate super high pressure?
Our lab is trying to synthesize the new material using the super high and temperature circumstances. Especially we synthesize by using two pieces of equipment to generate super high pressure called “diamond anvil cell” and “multi anvil press” Diamond is the most well-known jewel. Its shining appearance is attractive and seen as something new. Diamond, which is known as a jewel in general, is the hardest material in the world. If you squeeze material between diamonds, you can get extra-high pressure more than 1 GPa easily（Fig.１）．Diamond anvil cell is the extra-high pressure generating equipment based on this principle（Fig.4）．Diamond anvil cells is a small piece of equipment which can be carried in your hand, but it can generate super extra-high pressure, such as about 300 GPa, which is the same as the pressure in the center of the earth. Also, Diamond is transparent against wide wavelength. That means that it makes possible to make the state of very high temperature by irradiating an infrared laser through diamonds from outside to the materials of very high pressure inserted by the diamond anvil cell. In this way the combined system of diamond anvil cell (DAC) and infrared laser (LASER), LASER-DAC can create the world of Ultra high pressure Ultra high temperature.
On the other hand, multi anvil press isotopically pressurizes samples with the anvil of cemented carbide. By sending a current to the heater incorporated in the sample cell under high pressure, high pressure high temperature state occurs by joule heat. Pressure generation area in multi anvil device is smaller than diamond anvil, but it makes it possible to keep large capacity of sample volume and it is possible to measure physical property of composites by using the general evaluation device.
A mysterious world spread infinitely
LASER-DACUltra high pressure ultra-high temperature generation system was first made around 1970s. It has a 40 year history. LASER-DAC system is making progress with peripheral technology. Also, pressure generation area of multi anvil is expanding with the progress of technology. There is a report that pressure generation of 100 GPa was seen. As for the technology of generating ultra-high pressure, so far the research has been focusing on only the deep Earth related materials. However, materials are various and there is unlimited and unknown material science with the technology of generating super-high pressure such as using LASER-DAC, multi anvil press. Our lab has been enjoying the mysterious world of ultra-high and ultra-high temperature with young power and dream. We believe that those days will bring the creation of new knowledge and future materials.
Content of research
We have been developing the new creative technology of synthesizing the materials under ultra-high pressure and creating the new materials and new crystals of various inorganics, intermetallic compounds, and organic substances. We have been promoting the research about the synthetic reaction under ultra-high pressure and the process of crystal growth and crystal structure and the changes of physical property.
Major research themes
Creation of new inorganic substances and single crystal growth under ultra-high pressure
Elucidation of phase stability of materials under ultra-high pressure and high temperature
Elucidation of physical properties of new materials created under ultra-high pressure and high temperature
Synthesis under ultra-high pressure and development of in-situ measurement technology
Major research development high pressure synthesizing process and materials to be studied
Creation of new substances
Inorganic compounds, e.g. Nitride, oxide, phosphide, silicide, Germanium compound, intermetallic compound, carbide, boride
Singular structure
Layered compound, Kago like compound, nanotube crystal, quasicrystal, glass structure material, low-order compound, etc
Physical properties
Super hardness, electronic physical properties, elasticity, thermal expansion, lattice properties, superconductivity, luminescence properties, thermoelectric conversion properties, optical properties, magnetism
Contact :
Department of Materials Physics
Graduate School of Engineering, Nagoya University
Email : hasegawa@mp.pse.nagoya-u.ac.jp