|Budget Amount *help
¥1,800,000 (Direct Cost : ¥1,800,000)
Fiscal Year 1992 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1991 : ¥1,500,000 (Direct Cost : ¥1,500,000)
It is well known that liquid Hg is transformed to an insulating state when it is expanded up to the liquid-gas critical point (critical data of Hg: T_C=1478ﾟC, P_C=1673bar, d_c=5.8gcm^<-3>). A number of measurements of physical properties shows that, as the density is reduced, the metal-nonmetal (M-NM) transition starts to occur at a density of about 9 gcm^<-3>. The information on the atomic arrangement of expanded fluid Hg is quite important for understanding the M-NM transition. However, the diffraction experiments for expanded fluid Hg are not easy because the critical pressure is very high.
We have performed X-ray diffraction measurement for expanded fluid Hg in the temperature and pressure range up to 1530ﾟC and 1980bar, in the density region from 13.55 to 6.8 gcm^<-3>, using the energy-dispersive method. For the measurements, we have developed a single-crystalline sapphire cell and a high-pressure vessel of our own design, and improved the method of the data analysis. It has been found that the volume expansion of liquid Hg in the metallic region is not accompanied by a uniform increase of interatomic distance, r_1, but mainly caused by a decrease of coordination number, N_1. When the M-NM transition is approached, the rate of decrease of N_1 becomes small and r_1 starts to elongate. In addition, we have carried out X-ray diffraction measurement for dense Hg vapor in the density range from 3.5 to 1.5 gcm^<-3>, and obtained the result that, as the density of vapor Hg is reduced, the position of the first peak of the interference function, S(k), shifts remarkably to lower-k side.