X-ray diffraction measurements for expanded fluid mercury have been carried out in a wide density region from the liquid to dense vapour region using synchrotron radiation at SPring-8. We have ...developed a new high-pressure vessel with seven windows to collect the scattered X-rays for energy-dispersive X-ray diffraction measurements under high temperature and high pressure, and present the new data. It was found that the reliability of the structure factors,
S(
k), and the accuracy of the pair distribution functions,
g(
r), are much better. Reliable relations of the coordination number and the correlation distance with the density of fluid Hg were obtained. Structural changes with decreasing density are discussed in relation to the metal–non-metal transition in fluid Hg based on the new results.
Small angle X-ray scattering measurements for supercritical fluid metals such as selenium and mercury have been carried out using synchrotron radiation at SPring-8 to study density fluctuations near ...the liquid–vapor critical points. The absolute value of the scattering intensity was estimated from measurements on compressed He gas, a method developed using the in-house X-ray source at Hiroshima University. The observed scattering intensity of fluid selenium increases when one approaches the isochore of the critical density with decreasing pressure. The correlation length of the density fluctuations and the long wave length limit of the structure factor,
S(0), are deduced to be 16.5 Å and 31 at 1680 °C and 459 bar using the Ornstein–Zernike formula. Based on these data, the density fluctuations in fluid selenium are discussed.
X-ray diffraction measurements for expanded fluid selenium have been carried out in a wide density region from the liquid to the dense vapor using synchrotron radiation at SPring-8. We have developed ...a new high pressure vessel with seven windows to measure scattered X-rays and the reliability of the structure factors becomes much better. The measurements were made in the semiconductor–metal (SC–M) transition region from 600 to 1500 °C near 800 bar. The structure factors in the dense vapor region from 300 to 441 bar at 1650 °C are obtained for the first time. Structural changes in the SC–M transition region and the structure of the dense selenium vapor are discussed, based on these new results.
Small angle X-ray scattering (SAXS) measurements for dense Se vapour have been carried out to investigate the characteristics of the density fluctuations near the critical density region. For this ...reason the correlation lengths of the density fluctuations and the number-density fluctuations have been measured precisely at different temperatures and pressures near the critical point. In this experiment a new spectrometer with a high brilliance source is used and SAXS spectra are detected using an imaging plate. Less noisy spectra with better fitting conditions to calculate correlation lengths of density fluctuations are found. Larger values of the correlation length of density fluctuations (and also the number-density fluctuations) are obtained near the critical density region, which agrees with the results of our previous experiments J. Non-Cryst. Solids 250–252 (1999) 531. The correlation length of the density fluctuations increases as we approach to the critical point of fluid Se along the path of critical density region.
Energy-dispersive X-ray diffraction measurements using synchrotron radiation at SPring-8 for fluid Se have been carried out at temperatures up to 1650 °C and pressures up to 878 bar, including the ...dense vapour region, to investigate the structural change in the semiconductor-to-metal (SC–M) transition in expanded fluid Se. We obtained the structure factors,
S(
k), and the pair distribution functions,
g(
r), with a fairly good accuracy. Besides confirming the preservation of twofold-co-ordinated structure, the contraction of nearest co-ordination distance and the existence of asymmetry of the first peak in the
g(
r) in the metallic fluid region, it was found that the line shape of the first peak in the
g(
r) changes as well as the value of the first minimum in the
g(
r) increases obviously with increasing metallic properties. These results indicate that both the existence of different intrachain bonds and the interchain interaction are important for the mechanism of SC–M transition in fluid Se.
Small angle X-ray scattering (SAXS) measurements for fluid Se near the liquid–vapour critical point have been carried out to investigate the correlation between the density fluctuation and electronic ...properties of fluid Se near the isochore of critical density. For this purpose, correlation lengths of density fluctuations of fluid Se have been measured precisely at different temperatures and pressures near the critical point. In this experiment a side-by-side multi-layered mirror for Mo Kα
1 is used for monochromatizing and focusing X-ray beam for the first time. A better fitting condition to calculate the correlation lengths of the density fluctuation is found. Larger values of the correlation length of the density fluctuation are obtained near the critical density region.
EXAFS measurements around the Ge‐K edge have been carried out for liquid Ge‐Si alloys for the first time to investigate the local strucure around a Ge atom. To perform the EXAFS measurements for the ...liquid alloys with high melting temperatures, a new sapphire cell have been developed. The measurements were carried out for the liquid alloys from 10% to 60% of Si and the crystalline ones from 10% to 70% of Si as a reference. EXAFS oscillations, x(k), are observed even at 1480°C for liquid Ge0.4Si0.6. The position of the first peak in the radial distribution function obtained from Fourier transform of x(k) is shifted towards smaller distance for liquid and crystalline alloys with increasing Si concentration. The results of a curve‐fit analysis in a harmonic approximation show that Ge‐Ge and Ge‐Si bonds in the liquid alloys become long with increasing Si concentration while those become slightly short in the crystaline ones.
