Masanori Inui

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.

Ultrasonic Velocity and Density Measurement of Liquid Bi–Ga Alloys with Miscibility Gap Region

The measurement of ultrasonic velocity and sound attenuation, and density has been carried out for several liquid Bi–Ga alloys from the melting points to about 800°C. The ultrasonic velocity and its attenuation were determined by means of an ultrasonic pulse transmission method and the density was determined by a γ-ray absorption method. The adiabatic compressibility and molar volume of this system are obtained by the observed sound velocity and density. The temperature coefficient of the adiabatic compressibility is rather small in the concentration above the miscibility gap region than in the other concentration. The thermodynamic properties of this system are discussed based on the correlation between the structure and the compressibility.

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.

Electron Charge Distribution in Amorphous Se

The structure factors of amorphous Se at room temperature have been obtained by X-ray and neutron diffraction with sufficient accuracy. Although the coincedence of both structure factors is excellent, a clear difference has been found between X-ray and neutron diffraction results. The ion-electron correlation and valence electron distribution functions were evaluated from this difference. The obtained electron distribution function shows a broad peak at the distance around 1.0 A and the peak has a shoulder around 1.6 A. These may correspond to the distribution of the lone pair electrons and the covalent bonded electrons around a central Se ion, respectively.

EXAFS studies of liquid As2Te3 and GeTe2

Abstract The extended X-ray absorption fine-structure (EXAFS) spectra for liquid (l-) As 2 Te 3 around the As K-edge in the temperature range up to 900°C have been measured. For the measurements, a sample cell made of polycrystalline sapphire has been developed. A distinct EXAFS oscillation even at 900°C has been observed. From the detailed analysis of the EXAFS spectra, it is concluded that there exist As neighbors together with Te ones around As atoms in metallic l-As 2 Te 3 . EXAFS spectra for 1-GeTe 2 around the Ge K-edge up to 1000°C have been measured, and the existence of strong GeGe bonds in metallic l-GeTe 2 has been deduced.

Reverse Monte Carlo Simulations in Liquid Chalcogens

Using neutron diffraction data for liquid Se and Te, the Reverse Monte Carlo simulations have been performed. For liquid Se at the temperatures of 250°C and 350°C, the obtained structure mainly consists of two-fold coordinated chains, but about 30% of Se atoms have three-fold coordination and many Se 3 triangles are observed. For liquid Te a large number of Te atoms have three-fold coordination and the structure of liquid is network-like, which is very different from that of liquid Se.

Ultrasonic Velocity and Density Measurements of Molten CuCl–CuBr Mixtures

The ultrasonic velocity, sound attenuation and density measurements have been carried out for molten Cu(Cl 1- x Br x ) mixtures at temperatures from the melting points to about 800°C to investigate the thermodynamic and dynamical properties. The adiabatic compressibility of this system has obtained from the observed ultrasonic velocity and density. The observed compressibility has an interesting concentration dependence of positive deviation from linear one and has the maximum around Cu(Cl 0.2 Br 0.8 ), which suggests large fluctuations in the molten mixtures compared with pure molten CuCl and CuBr. The sound attenuation shows large temperature dependence around x =0.2 and 0.8. We discuss the thermodynamic and dynamical properties of the molten mixtures from a view point of chemical bond, taking the difference of ionicity between Cl and Br into account.

Structure of chalcogen nano-droplets

Abstract The structure of chalcogen nano-droplets consisting of Te and SeTe mixtures, dispersed in NaCl or KI matrices in supercooled states down to 250°C, was studied. EXAFS experiments show that the twofold coordinated chain structure remains and that the chain consists of shorter bonds (2.8 A) and longer bonds (3.0 A). The fraction of longer bonds is reduced as the temperature decreases. The result of neutron diffraction measurement suggests that the mean chain length of liquid Te is short and the chains tend to have planar zigzag geometry, which is similar to the local structure of the high pressure metallic crystal. When liquid Te is strongly supercooled, it is found that the zigzag chain transforms to a helical chain.

EXAFS Measurement of Molten Cuprous Halides

EXAFS measurement of molten CuCl and CuBr has been carried out near the melting temperatures in order to study the partial structure. EXAFS oscillation was clearly observed and the structural parameters for the nearest neighboring Cu-halogen pairs were obtained from standard curve fit analyses. The obtained Cu-halogen distance is, however, about 0.1A shorter than the distance obtained from neutron diffraction measurement with isotopic substitution. The result may suggest cluster formation such as a CuX trimer (X = Cl, Br) in molten cuprous halides.

Structural Study of Liquid Bi-Ga Alloys with Miscibility Gaps

The structure of liquid Bi–Ga alloys has been examined by neutron scattering measurements. The structure factors of this system have been obtained along the liquidus curve and also at higher temperatures above the critical temperature where the miscibility gap closes. A remarkable change in the structure factor has been observed at around 70 at.%Ga, which composition corresponds to the maximum temperature in the curve where miscibility gap closes. This concentration variation of the observed structure factors has been discussed in view point of the thermodynamic properties.