Kenji Maruyama

Mass-fractal clustering and power-law decay of cluster size in 1-propanol aqueous solution

Mesoscale structure of 1-propanol aqueous solutions with propanol mole fraction xp ranging from 0.1 to 0.33 has been studied by means of small angle neutron scattering (SANS) and large-scale reverse Monte Carlo (RMC) technique. Analysis of the SANS intensities in terms of a fractal model shows that the fractal dimension df of mesoscale structure of the solution is about 1.8-1.9 for water-rich solution and about 1.5 for propanol-rich solution. Percolation analysis on the RMC results reveals that the water molecules and the propanol molecules cluster, respectively, as a mass fractal, the dimension dM of which is about 2.3-2.5 for both clusters for water-rich solution. Furthermore, the distribution of the cluster size is expressed by a simple power law with an exponent tau of about 1.35-1.5 for the propanol clusters and 1.05-1.2 for the water clusters. These results imply that the current solution is characterized by polydisperse mass fractals. In fact, a theoretical relation for polydisperse system of mass fractals, df = dM(2-tau), holds well in the current solution. The characteristic change in df from 1.8-1.9 to 1.5 described above is attributed to the crossover between the water-rich regime and the propanol-rich regime. Most of the water molecules and the propanol molecules are located on the interface between clusters, and the water molecules form thin layers of about 10 A thick irrespective of 1-propanol content studied.

Small angle neutron scattering study on the salt-induced phase separation of 1-propanol aqueous solution

Small angle neutron scattering (SANS) measurements have been carried out over a wide range of Q from 0.003 to 7 A−1 on the 1-propanol-water solution with KCl and that without KCl in relation to the salt-induced reentrant phase-separation phenomena. The Q dependence of the SANS intensity for both solutions is characterized by the same fractal structure with the fractal dimension df of 1.9. The only difference between the two solutions is the value of correlation length ξ. In the solution without KCl the value of ξ is rather small, ranging from 7.4 to 6.2 A depending on temperature, while in the solution with KCl it becomes very large, from 48 to 355 A or more depending on temperature, and diverges toward the phase-separation temperatures in a similar way for both the upper and lower one-phase regions. No significant differences have been found on the growing structure of fluctuation in the upper and lower one-phase regions.

Salt-induced phase separation in aqueous solution

Abstract KCl-induced phase separation phenomenon in 1-propanol aqueous solution has been studied by means of small angle (SANS) and quasi-elastic neutron scattering measurements. The significant increase of SANS intensity by the addition of KCl is attributed to the aggregate of clusters, of which the fractal nature of dimension 1.8–1.9 is found. The motion of water molecules is much suppressed in the 1-propanol–water solution, while it is slightly recovered by the addition of KCl. The aggregate of clusters and liquid–liquid phase separation are discussed in relation to the motion of water molecules.

Quasielastic neutron scattering investigation of motion of water molecules in n-propyl alcohol-water mixture

The dynamics of water molecules in the n-propyl alcohol-water mixtures is investigated by using quasielastic neutron scattering measurements. The dynamic structure factor S(Q,E) obtained from incoherent scattering of hydrogen atoms of water is fitted with jump diffusion and relaxing cage models. The diffusion constant obtained from the relaxing cage model, which gives better fitting with S(Q,E), shows better agreement to the experimental value than that of jump diffusion model. The dependence of translational relaxation time tau(T)(Q) and stretched exponent beta(T)(Q) on the fraction of hydrophobic hydrating water molecules in the solution is discussed.

Structure and dynamical properties of liquid In2Te3

Abstract Liquid In–Te has a compound-forming behavior around the In 2 Te 3 composition. The large temperature dependences of many physical properties at this composition are strongly related to structural changes in this liquid. Energy dispersive X-ray diffraction measurements were carried out to study the change of the local structure in liquid In 2 Te 3 with temperature over a wide temperature range up to 1200 °C. The observed total structure factor, S ( Q ), shows a distinct second peak around 3.05 A −1 at lower temperatures and, with increasing temperature, this peak decreases, becoming a small shoulder at the highest temperature. The neutron diffraction spectra for liquid In 2 Te 3 was also measured at 750 °C and a similar profile for S ( Q ) to the X-ray results was obtained. The formation of triangular-pyramidal units just above the melting point and the appearance of chain like molecules in the high temperature liquid are proposed, along with a bond fluctuation model.

Local structure of molten Ag(Cl1-xIx) mixtures

Abstract Neutron diffraction and EXAFS measurements have been carried out on molten Ag(Cl 1− x I x ) to investigate the local structure of these mixtures. From the observed structure factors by neutron diffraction for all concentrations, the characteristic prepeak can be observed in the smaller Q regions, which we suggest indicates a kind of cluster formation of halogen ions around a central cation. From EXAFS results, at eutectic composition, the partial coordination numbers of Cl ions around an Ag ion decrease and the coordination shell has an asymmetrical distribution with increasing temperature. The local structure in the eutectic region has been provided and discussed in relation to the anomalous effects of ultrasonic absorption of this mixture.

Neutron Diffraction Studies on the Liquid Te and As–Te Mixtures

Neutron diffraction measurements for liquid (l-) Te and l-As–Te mixtures (10, 20, 30 and 40 at.% As) have been performed. The first minimum after the first peak of g ( r ) for l-Te and l-As–Te mixtures is filled up with temperature, and the second peak diminishes substantially and flattens out at high temperature. The temperature variations of g ( r ) are discussed combining the structural information available from EXAFS and computer simulation results. We propose that the volume contraction near the semiconductor to metal (S–M) transition causes the shrinkage of the inter-chain distance, and the short- and long-distance inter-chain correlations may coexist at high temperature. In the metallic region the –As–Te– chains are inferred to have nearly the same configuration as in l-Te. The prepeak near Q =1.1 – 1.5 A -1 is observed for l-As 20 Te 80 and l-As 40 Te 60 , which diminishes with increasing temperature. The prepeak in l-As 40 Te 60 lies at lower Q region compared with l-As 20 Te 80 . It is conclude...

Intra-and Intermolecular Correlations in Liquid Selenium-Halogen Systems

The structure of liquid (l-) selenium-halogen mixtures has been studied by both EXAFS and neutron scattering measurements. The concentration variation of the coordination numbers of Se and halogen atoms around the central Se atom were determined. It was found that all Cl atoms in l-Se 1- x Cl x act as chain terminators. The rapid contraction of Se-Se and Se-Cl bonds was observed when the Cl concentration approached 0.5. For l-Se 1- x I x , I atoms are not always incorporated into the chain molecules, and the excess I atoms form I 2 molecules. The intermolecular orientational correlation for l-Se 0.5 Cl 0.5 and l-Se 0.5 Br 0.5 will be discussed utilizing the results of the neutron scattering experiments.

Mössbauer Studies on the Tellurium-Selenium Mixed Chains

125 Te Mossbauer absorption measurements have been carried out for Te-Se mixed chains confined in the one-dimensional channels of mordenite crystals as well as for the mixed chains in trigonal crystalline and amorphous phases. 129 I Mossbauer emission spectra have been also taken for 129 Te labeled amorphous and trigonal Te-Se mixtures. The quadrupole splitting at the 125 Te atom is found to be appreciably larger for the isolated chains than for the trigonal mixtures, suggesting that the anisotropy of Te bonding is increased by reducirng the interchain coupling between the adjacent chains. Both 125 Te and 129 I Mossbauer results indicate that the molecular character is much stronger in the amorphous phase than in the trigonal phase.

Key experimental information on intermediate-range atomic structures in amorphous Ge2Sb2Te5 phase change material

Laser-induced crystalline-amorphous phase change of Ge-Sb-Te alloys is the key mechanism enabling the fast and stable writing/erasing processes in rewritable optical storage devices, such as digital versatile disk (DVD) or blu-ray disk. Although the structural information in the amorphous phase is essential for clarifying this fast process, as well as long lasting stabilities of both the phases, experimental works were mostly limited to the short-range order by x ray absorption fine structure. Here we show both the short and intermediate-range atomic structures of amorphous DVD material, Ge2Sb2Te5 (GST), investigated by a combination of anomalous x ray scattering and reverse Monte Carlo modeling. From the obtained atomic configurations of amorphous GST, we have found that the Sb atoms and half of the Ge atoms play roles in the fast phase change process of order-disorder transition, while the remaining Ge atoms act for the proper activation energy of barriers between the amorphous and crystalline phases.