Kenichi Kinugawa

Raman spectroscopic study on the structure of ZnCl2ZnX2 and ZnCl2KX (X = Br, I) glasses

Abstract Raman spectra have been measured for ZnCl 2 ZnX 2 and ZnCl 2 KX (X = Br, I) glasses to investigate the structure of the glasses with varying composition. The assignment of each band was made, and the change of the spectra with composition was explained in terms of the bridging and non-bridging states of halide ions and the change of the tetrahedral units, ZnX n Cl 4− n 2− ( n = 0–4), formed in the glasses. As the content of ZnX 2 in ZnCl 2 ZnX 2 glasses increases (20 → 80 mol%), the peak frequency of the ZnCl stretching mode increases (238 → 248 cm −1 in X = I glasses, 238 → 259 cm −1 in X = Br glasses) while the ZnI and ZnBr stretching frequencies decrease (173 → 120 cm −1 for ZnI, 196 → 157 cm −1 for ZnBr). The decrease of the ZnI and ZnBr band frequencies was attributed to the increase of the number n of the ZnX n Cl 4− n 2− tetrahedra. The increase of the ZnCl frequency suggests the existence of the bonding state of Cl − ions which is intermediate between the bridging and the non-bridging states. In ZnCl 2 KX glasses, the ZnCl non-bridging band at about 300 cm −1 was observed in addition to the bands observed in ZnCl 2 ZnX 2 glasses. The addition of KX produces non-bridging anions while the tetrahedral units, ZnX n Cl 4− n 2− are also formed.

Collective dynamics of alkali chloride glasses: Molecular dynamics analyses of the dynamic structure factors

The collective dynamical properties of two glassy alkali chlorides [pure LiCl and the mixture 50(mol %) LiCl–40 KCl–10 CsCl] have been investigated by using molecular dynamics simulations. On the basis of van Hove’s description of the microscopic density fluctuations, the dynamic structure factors S(k,ω) have been calculated for 0.3≤k≤5.9 A−1 to reveal phonon excitation and motional correlations between each ionic species. Examining the phonon dispersion curves, it is found that there are one longitudinal acoustic and two longitudinal optic branches in both glasses. In the LiCl glass, collective vibrations of the Li+ and Cl− ions are spatially delocalized for k≤1.6 A−1 and are strongly correlated with each other. On the other hand, in the mixture glass, collective motions of the Li+ ions are almost independent of those of the Cl− ions. In this glass, there are the intense longitudinal optic (LO) vibrations localized on single Li+ ions, similar to an Einstein oscillation. The LO mode frequency for k≥1.5 A−...

Novel halide glasses based on systems of LiX (X = Cl, Br, I)

Abstract New halide glasses have been obtained in systems of LiXKXCsXBaX2 (X = Cl, Br, I) where the main component is LiX. The glasses first discovered are those which contain only alkali halides and alkaline earth halides. Glass transition and crystallization temperatures were in the range of 40–80°C and 65–105°C, respectively. The IR cut-off wavelength is beyond 10 μm. These glasses have high ionic conductivity, e.g., for the LiI-based glass, 5.8 × 10−7 S/cm at 25°C.

Preparation and vibrational spectroscopy of ZnI2-based glasses

Abstract Glass formation has been examined in the systems based on ZnI 2 . Glasses are obtained in ZnI 2 CsIMI 2 (M  Ba, Pb) and ZnI 2 CsIBaI 2 M′I (M′  Tl, Ag) systems. Raman and far IR spectra have been measured for the ZnI 2 CsIBaI 2 glasses and crystals of ZnI 2 and Cs 2 ZnI 4 . Raman spectra of the glasses have two highly polarized bands at 113 cm −1 and 124 cm −1 , while in far IR spectra strong and broad overlapping absorption bands at 152 cm −1 , 173 cm −1 and 197 cm −1 are observed. A comparison with the spectra of ZnI 2 and Cs 2 ZnI 4 crystals indicates that the glasses have a structure consisting of ZnI 4 tetrahedra sharing corners. The bands of the glasses are assigned as follows: the 113 cm −1 and 124 cm −1 bands are due to the symmetric modes containing stretching vibrations of Zn-bridging I( b I) and Zn-non-bridging I( nb I) of ZnI 4 tetrahedra, respectively, and the 152 cm −1 and 197 cm −1 bands are due to the antisymmetric modes of the Zn- b I stretching vibration and the 173 cm −1 band to the antisymmetric mode of the Zn- nb I stretching vibration. These assignments are consistent with the compositional variations of the spectra.

Pulsed neutron diffraction study on the structures of glassy 7LiX–KX–CsX–BaX2 (X=Cl, Br, and I)

The structures of glassy 7LiX–KX–CsX–BaX2 (X=Cl, Br, and I) have been investigated by means of pulsed neutron diffraction experiment. The obtained total radial distribution functions were discussed with the help of the molecular dynamics simulation based on the Tosi–Fumi potential. The Li–X (X=Cl, Br, and I) distances in the three glasses are 2.37, 2.49, and 2.70 A, respectively, which are 0.2–0.3 A shorter than those in the rocksalt‐type LiX crystals. For each system, it is found that the coordination number of the X− ions around the Li+ ions is about four when only the closely contacting X− ions are counted. Because of the 1:1 monovalent character of the present systems, the first coordination shell around the Li+ ions has the ill‐defined outer extent, compared with the 4:2 and 2:1 charged systems such as SiO2 and ZnCl2. This causes the increase of the coordination number, from four to six, when all the near‐neighbor X− ions are counted as the surrounding ions.

Dynamical properties of an alkali chloride mixture in the glassy and liquid states

Molecular dynamics calculations have been carried out to reveal the dynamical properties of an alkali chloride mixture (50 mol% LiCl40KCl10CsCl) and pure LiCl in the liquid and glassy states. It is found that the mobility of Li+ ions in the mixture is significantly lower than that in LiCl, not only in liquid state but also in the glassy state. The partial dynamic structure factors, SLiLi (Q, ω) and SClCl (Q, ω), are evaluated to investigate the dynamical correlation between the Li+ and Cl− ions. In LiCl glass, it is shown that the motions of the Li+ and Cl− ions are highly correlated with each other, and both the acoustic and optic modes are spatially delocalized (Q < 1.8 A−1). On the other hand, in the mixture glass, the motion of the Li+ ions is almost independent of that of the Cl− ions, and at small wavelengths there are the intense vibrations localized on single Li+ ions similar to an Einstein oscillation.

Ionic dynamics on the potential energy surfaces of glassy alkali chloride systems

Molecular dynamics calculations are carried out for two Coulombic glasses, LiCl and LiCl‐KCl‐CsCl. Stillinger‐Weber’s inherent structures (the configurations of potential minima) which ions in glassy state undergo during 100 ps were explored for two systems. The ions in the LiCl‐KCl‐CsCl glass diffuse collectively via the successive potential basins whose minima are distributed along zigzag ways. On the contrary, in pure LiCl glass several ions transit to the next potential basins while the remaining ions continue to stay at almost the same potential basins.

New halide glasses based on systems of CuX (X=Cl, Br, I)

On etudie la formation vitreuse des systemes: CuX-MX-BaX 2 ou M=K, Rb ou Cs et X=Cl, Br ou I. On presente les proprietes thermiques et optiques de ces verres. On discute la formation vitreuse du point de vue de la structure cristalline

MOLECULAR DYNAMICS SIMULATION OF MIXED ALKALI HALIDE GLASS

Isobaric-isothermal molecular dynamics calculations have been carried out to reveal the microscopic structure of the glass of the mixed alkali chloride system 50LiCl-40KCl-10CsCl. The glass state is achieved below the calculated glass transition temperature about 600 K, by cooling the liquid at the quenching rate of 5×10 13 Ks -1 . It is found that the tetrahedral short-range order, LiCl 4 , is well-defined and is predominant in number, in the structure of the 300 K glass. Two neighboring tetrahedra are mutually connected not only by sharing a vertex Cl ion but also by sharing an edge of the tetrahedra in another case. Moreover, even 45 % of the vertex Cl ions is shared by more than two LiCl 4 tetrahedra. Such structural feature has never been observed in the conventional inorganic glasses, and also indicates the novelity of this mixed alkali chloride glass.