Osamu Uemura's research while affiliated with Yamagata University and other places

The environmental structure around Li+ in highly concentrated solutions has been investigated through measurements of isotopic substitution-neutron diffraction and the low-frequency isotropic Raman spectra. The least-squares fitting analysis has been adopted for the Li+ difference interference function, ΔLi(Q), observed for 25 mol% LiBr and 33 mol% LiI methanolic solutions, and for 12 mol% DCOOLi and HCOOLi aqueous solutions, in order to determine the structure parameters on the solvated ion-pair Li+ ... X- (X: Br, I and DCOO) in these solutions. It has been found that the first solvation shell of Li+ in these highly concentrated solutions is significantly modified by the nearest neighbor counter ions.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Measurements of the electrical conductivity, magnetic susceptibility and thermoelectric power have been carried out on liquid Ag-As2Te3 and Ag-As2Se3 systems. The liquid Ag-As2Te3 system exhibits a deep minimum of the electrical conductivity, diamagnetic peak of the magnetic susceptibility and rapid drop of the positive thermoelectric power at the stoichiometric composition of Ag6As2Te3, reflecting the occurrence of the metal-semiconductor transition. The liquid Ag-As2Se3 system also has the diamagnetic peak of magnetic susceptibility and sign reversion of thermoelectric power near the composition of Ag6As2Se3. However, the electrical conductivity in the selenide system indicates a negative temperature dependence like metals and takes a maximum value at this composition. The observed results have been discussed with the help of the pseudogap model developed by Enderby and Barnes. In this result, the unusual behavior of electrical conductivity in the selenide system has been deduced to be associated with the conduction and valence band edge-parameters rather than the pseudogap width.

Ductile amorphous and nanocrystalline M–W (M = Fe, Ni) alloys were produced by electrodeposition. The structural studies of these alloys were carried out by using extended X-ray absorption fine structure (EXAFS) and small angle X-ray scattering (SAXS) methods. The crystal structure of the electrodeposited Ni–W alloy was similar to that of Ni4W phase. The nearest Ni–Ni distance was determined to be 2.49Å, Ni–W distance was determined to be 2.50Å. The average crystal-grain size of the as electrodeposited Ni–W alloy was estimated to be about 2.5nm from Guinier plot of SAXS spectra. The electrodeposited Fe-21.6at.% W alloy has short range order, but not any medium range order around Fe and W atoms, it possesses amorphous structure. The nearest Fe–Fe and Fe–W distances in the alloy were determined to be 2.42 and 2.53Å, respectively. The structures of mechanically alloyed (MA) M–W (M = Fe, Ni) alloys are similar to that of the as electrodeposited M–W (M = Fe, Ni) alloys. But these alloys include a small amount of undissolved pure Fe, Ni and W, also.

Time-of-Flight (TOF) neutron diffraction measurements have been carried out on aqueous 3 mol% D,L-alanine solutions. The isotopic substitution technique has been applied to both nitrogen and methyl-hydrogen atoms within the alanine molecule in order to obtain information concerning the hydration structure around the amino- and the methyl groups within the alanine molecule in the aqueous solution. There exist, on the average, 2.4(1) water molecules that are hydrogen bonded to the amino group with an intermolecular distance of rNO = 2.88(2) Å. The tilt angle between the N–D···O axis and the molecular plane of the D2O molecule has been determined to be 60.4(5)°. The first hydration shell of the methyl group involves ca. two water molecules per one alanine molecule. The nearest neighbor HM(methyl)–OW(water) and HM(methyl)–HW(water) distances have been determined to be 2.58(1) and 2.99(2) Å, respectively.

Amorphous GeSe2, Ge3Se4 and Ge4Se5 have been prepared by mechanical milling (MM), and their structural changes have been investigated by X-ray diffraction, Raman scattering and EXAFS measurements. Amorphous Ge4Se5 was obtained at the milling time of 50 h in the present experiment, which has never been obtained by the rapid quenching from the melt. The short-range order in GeSe2 remains almost unchanged during the milling. Since the configuration of tetrahedral units in the crystalline phase becomes rapidly less ordered with increasing the milling time, the amorphization is complete at a short milling time. On the other hand, Ge3Se4 and Ge4Se5 samples, both of which are eutectic mixtures of intermediate compounds of GeSe2 and GeSe, need longer milling times for the amorphization, as they are accompanied by the change in local structures. The short-range order in these Ge-Se alloys is described by covalent 4(Ge)-2(Se) folded coordination structure. The structural feature of crystalline GeSe phase with a partial ionicity, i.e. 3(Ge)-3(Se) folded coordination, disappears not only in amorphous Ge3Se4 but also in amorphous Ge4Se5, where the concentration ratio of Ge/Se is close to that of the stoichiometric composition of GeSe. The bond-lengths of Ge-Se and Ge-Ge in these amorphous alloys are determined to be 0.236 and 0.248 nm, respectively, which are consistent with the corresponding covalent distances.

Neutron diffraction measurements with N-14/N-15 and H/D isotopic substitution methods have been carried out on aqueous 15 mol% urea solutions, in order to obtain information on the hydration structure of the amino group within the urea molecule in concentrated aqueous solutions. The observed first-order difference function, (0H)Delta(N)(Q), and the N-H partial structure factor, alpha(NH)(Q), were analyzed by the least squares fitting procedure. The nearest neighbor N...O and N...H distances were obtained to be 2.92(l) Angstrom and 3.42(l) Angstrom, respectively. The average hydration number per one amino group was determined to be 2.0(1). The tilt angle between the N-H...O axis and the molecular plane of the hydrogen bonded water molecule is estimated to be 51(5)degrees.

X-ray diffraction, EXAFS and Raman spectroscopic studies, together with transport phenomena measurements, have been carried out for (AgI)x(As2Se3)1−x glasses in order to investigate the ionic conduction mechanism in AgI doped non-oxide glasses. The addition of AgI into As2Se3 glass is responsible for a pronounced increase in the electrical conductivity. Particularly, the ionic component of the electrical conductivity is dominant in highly doped glasses. Results of Raman spectra, EXAFS measurements and least squares fitting analysis for observed X-ray structural functions suggest that the local structure of the present glasses can be described as a pseudo-binary mixture of As–Se networks and fourfold coordinated AgI clusters.

X-ray diffraction and ATR-IR spectroscopic measurements have been carried out for HCOOK hydrated melts, (HCOOK)x(H2O)1−x with x=0.3, 0.35 and 0.40, in order to obtain structural information on both the ion–water and ion–ion interactions in extremely concentrated aqueous solutions. The observed X-ray intermolecular interference terms were analyzed through the least-squares fitting procedure. The present value of the nearest neighbor K+⋯H2O distance, rK+⋯H2O=2.77(1) Å, for the 40 mol% HCOOK solution is in good agreement with that observed in various aqueous solutions. On the other hand, the coordination number, nK+⋯H2O, was revealed to be 2.6(1), which is much smaller than the value, nK+⋯H2O∼6, reported for more dilute aqueous solutions. Structural parameters for the contact ion pair, HCOO−⋯K+, were satisfactorily determined to be rO(HCOO−)⋯K+=2.80(1) Å, nO(HCOO−)⋯K+=1.3(1) and ∠C–O⋯K+=100(1)°, respectively. Hydration numbers, such as nK+⋯H2O and nHCOO−⋯H2O were found to be strongly concentration dependent from the ATR-IR spectra for uncoupled O–D stretching vibrational bands of HDO molecules in the melts.