Development of ultrahigh pressure apparatus based on high pressure produced by constraining expansion due to breaking of bonds between atoms and between molecules

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An ultrahigh-pressure apparatus is proposed where pressures are generated by constraining expansion due to breaking of bonds in matter. Glassy carbon constrained by a sapphire anvil cell was irradiated through one anvil with a pulsed YAG laser. A measurement of fluorescence emission from a ruby in the sample chamber was made. A measurement of reflectivity of a diamond was also made in the experiment using the sapphire and diamond anvils for volume constraint. A pulsed X-ray diffraction device was developed to measure transiently generated pressures, which was assembled into the apparatus. The results are as follows: 1. Pressures beyond 300 GPa were achieved for 〜1 ms in the sapphire cell. 2. The fluorescence emission over a wide wavelength range observed in the diamond cell arises from the pressure-induced ^4T_2→^4A_2 transition in ruby, which seems not to result from the pressure-induced diamond fluorescence. 3. High reflectivity suggesting the metallization of diamond was observed at the interface between the diamond crystal and anvil. 4. The observed dislocation density for the diamond is comparable to those for highly deformed crystals, suggesting large plastic deformation of the diamond. 5. As is theoretically predicted by Nielsen, the diamond may have metallized at a uniaxial stress near 400 GPa. 6. The output of pulsed laser required to generate high pressures in the apparatus is some orders of magnitude less than those in the conventional methods. 7. Diffraction data can be obtained from a very small amount of metal powder using the pulsed X-ray diffraction device. 8. The volume of the unit cell for the metal can be determined from the diffraction data. Although several technical problems to be settled for detecting diffracted X-ray from a sample still remain, researches on high-pressure phase of matter in the terapascal region will be started in the near future.