Shinya Hosokawa

X-ray diffraction measurements for expanded liquid mercury in the metallic region

X-ray diffraction measurements for expanded liquid Hg have been carried out for the first time in the density range from 13.55 to 10.26 g cm-3, covering almost all of the metallic region of expanded liquid Hg. The authors have developed a new type of high pressure vessel and a new sample cell made of single-crystal sapphire for the X-ray diffraction measurements using the energy-dispersive method. They have obtained the structure factor and the pair distribution function as functions of density. It was found that the nearest-neighbour distance remains almost constant increasing slightly, less than 1%, with the reduction of density by about 24%. On the contrary, the coordination number decreases substantially and almost linearly with decreasing density. The volume expansion of liquid Hg in the metallic region is not accompanied by a uniform increase of interatomic distance but is mainly caused by a decrease of coordination number.

EXAFS measurements of liquid Se-Te mixtures

The authors have measured EXAFS spectra of liquid(1-)Se, Te, Se-Te mixtures and vapour (v-)Se for the first time. It is clearly observed that the two-fold coordinated chain structure is largely preserved in l-Se and that the intrachain covalent bond contracts on melting. The EXAFS spectra of l-Te can be reproduced well by assuming a two-fold coordinated chain structure with shorter and longer bonds within the chain. In order to obtain partial structure-parameters in liquid Se-Te mixtures, spectra are taken on both Se and Te K edges. The Se-Se bond elongates with increasing Te concentration. The number of the longer Te-Te bonds increases with increasing temperature or increasing Te concentration; this may be associated with the semiconductor-to-metal transition.

XAFS measurements at high temperatures and pressures

The method of XAFS measurements at high temperatures and pressures for supercritical fluids with high critical constants have been developed. An internally heated high‐pressure vessel made of super‐high‐tension steel and a polycrystalline sapphire cell of our own design permit XAFS measurement up to 800 bar. XAFS experiments were carried out at high temperatures up to 1600 °C, and high pressures up to 150 bar. XAFS spectra of liquid Se at 1300 °C and 150 bar, and dense Se vapor at 1600 °C and 150 bar have been obtained and clear oscillations are observed at these temperatures.The method of XAFS measurements at high temperatures and pressures for supercritical fluids with high critical constants have been developed. An internally heated high‐pressure vessel made of super‐high‐tension steel and a polycrystalline sapphire cell of our own design permit XAFS measurement up to 800 bar. XAFS experiments were carried out at high temperatures up to 1600 °C, and high pressures up to 150 bar. XAFS spectra of liquid Se at 1300 °C and 150 bar, and dense Se vapor at 1600 °C and 150 bar have been obtained and clear oscillations are observed at these temperatures.

Extended x‐ray absorption fine structure studies of dense selenium vapor

We have measured the extended x‐ray absorption fine structure spectra for dense selenium vapor at high temperatures and pressures up to 1600 °C and 150 bar for the first time. For the experiment, we have developed a high‐pressure vessel and a polycrystalline sapphire cell of our own design. We have found that dense selenium vapor under the present experimental condition consists mainly of Se2 and the bond length is much shorter than that of liquid Se. With increasing pressure the bond length slightly increases. When the saturated vapor‐pressure curve is approached, the bond is largely elongated.

Optical absorption spectra of liquid As2S3 and As2Se3 over a wide temperature range

The authors have measured the optical absorption coefficient of liquid As2S3 and As2Se3 up to 900 degrees C in a wide absorption range up to about 3*105 cm-1. They have developed an optical cell of their own design with a sample thickness of about 2000 AA. The optical gap obtained from the spectra decreases rapidly with increasing temperature, eventually becoming zero at about 950 degrees C for liquid As2Se3, where the semiconductor-to-metal transition starts to occur.

Density measurement for fluid selenium by the X-ray absorption method

The density of fluid Se was measured at temperatures up to 1670°C and pressures up to 700 bar by means of X-ray absorption. This is the first measurement which extends over the entire liquid-gas range, including the supercritical region. For the measurement specially constructed sapphire cell was used. Fluid Se has a critcal point at Tc=1630−30+0°C, Pc=380±2bar and ϱc=1.85±0.05 g/cm3. The equation of state and its derivatives such as isothermal compressibility and thermal expansion coefficient are presented.

Zn, Mn and Te K-edge EXAFS studies of the diluted magnetic semiconductor

Extended x-ray absorption fine-structure measurements at the Zn, Mn and Te K edges of the diluted magnetic semiconductors have been performed to investigate the local coordination around each of the atoms. The nearest-neighbour and next-nearest-neighbour interatomic distances are found to be almost unchanged on changing the Mn concentration (x). These results indicate that the tetrahedral and clusters are embedded in the alloys with a well-preserved form, in agreement with the x-independent Mn 3d partial density of states derived from resonant photoemission measurements.

EXAFS measurements for liquid As2Se3 at high temperatures and pressures

Extended X-ray absorption fine structure (EXAFS) spectra from liquid As2Se3 around both the As and Se K-edges in the temperature-pressure range up to 1400°C and about 60 bar were measured. For the EXAFS measurements, a new type of high pressure vessel and a sample cell of own design made of polycrystalline sapphire were developed. Distinct EXAFS oscillations were obtained even at 1400°C. When the semiconductor-to-metal transition occurs at about 1000°C, the local environment around a central As atoms is substantially changes and a new As neighbor site is induced.

Optical absorption spectra of fluid selenium near the nonmetal-metal transition region

Abstract The optical absorption coefficient of fluid Se was measured in the energy range of 0.5–4.5eV at temperatures up to 1700°C and pressures up to 500 bar. Measurements were made by use of quartz and sapphire cells. The optical path lengths were 5mm to 3000A, which enabled us to obtain the absorption coefficient in the wide range extending to the value of 2×105cm−1. The optical gap was for the first time derived derived from the analysis of the spectra in such a high absorption region. The optical gap substantially decreases with temperature and pressure eventually to vanish near the liquid-gas critical point.

Structural changes in expanded fluid mercury: from liquid to dense vapour

The energy dispersive X-ray diffraction measurements for expanded fluid Hg have been carried out up to the sub- and supercritical regions. The dense vapour near the critical region has also been studied. We have obtained the structure factors and the pair distribution functions as functions of temperature (RT-1530 degrees C), pressure (5-1970 bar) and density (13.55-1.86 g cm-3).