Toshinobu Yoko

Waveguide formation in niobium tellurite glasses by pico- and femtosecond laser pulses

Abstract We obtained a temporal and permanent refractive index change in niobium tellurite glasses by using ps- and fs-pulses, respectively. A He–Ne laser beam was guided by a line waveguide structure drawn by the fs-pulses, indicating positive refractive index change. It is suggested that the refractive index change by the ps-pulses is due to an increase in the absorption coefficient while that caused by the fs-pulses results from the rearrangement of the glass structure.

Preparation and surface properties of silica-gel coating films containing branched-polyfluoroalkylsilane

Abstract Composite coating films crack-free and with smooth surfaces have been prepared by the sol–gel technique using branched chain polyfluoroalkylsilane (triethoxy[4,4-bis(trifluoromethyl)-5,5,6,6,7,7,7-heptafluoroheptyl]silane) (D3Et) and tetraethoxysilane (TEOS) as starting materials. Surface properties of the fluorinated coating films heated at various temperatures were examined in comparison with films derived from methyltrimethoxysilane (MTM) and TEOS, based on the measurements of infra-red spectra, thermal gravimetric changes and X-ray photoelectron spectra and contact angle of water and diiodo methane. It was found that the fluorosilane-containing films had thermal stability and surface energies, γ s , as small as polytetrafluoroethylene (PTFE) up to 400°C and a large contact angle of water comparable to the films derived from MTM and TEOS. Large hydrophobicity of fluorosilane-containing films seems to be due to the dispersion component of the surface energy compared with methyltrimethoxysilane and TEOS films. We conclude from X-ray photoelectron spectra measurements that the surface energy of the fluorinated coating film originate from polyfluorocarbon molecules at the topmost film surface.

The local structure of Sm-doped aluminosilicate glasses prepared by sol–gel method

Abstract The local structures of Sm and Al in Sm-doped aluminosilicate glasses prepared by the sol–gel method were investigated by using 27Al MAS NMR spectroscopy and X-ray radial distribution function (RDF) analysis. It is found that at low alumina content (1 mol%), the glass network consists of SiO4 and AlO6 structural units. At higher alumina content, AlO4 and AlO6 structural units coexist in the glasses. It is considered that the formation of AlO4 results in enhancement of the dispersion of Sm ions in these glasses. The average coordination number of Sm in a 10Al2O3xa0·xa090SiO2xa0·xa01Sm2O3 glass slightly increased from 7.1 to 8.5 after heat-treatment in reducing atmosphere. The role of Al ions in dispersing Sm ions in a glass matrix is discussed.

Structure of alkali tellurite glasses from neutron diffraction and molecular orbital calculations

The structure of pure TeO2 and alkali tellurite glasses has been examined by neutron diffraction and ab initio molecular orbital methods. The experimental radial distribution functions along with the calculated results have demonstrated that the basic structural units in tellurite glasses change from highly strained TeO4 trigonal bipyramids to more regular TeO3 trigonal pyramids with increasing alkali content. It has also been shown that the TeO3 trigonal pyramids do not exist in the form of isolated units in the glass network but interact with each other to form intertrigonal Te⋯O linkages. The present results suggest that nonbridging oxygen (NBO) atoms in tellurite glasses do not exist in their “pure” form; that is, all the NBO atoms in TeO3 trigonal bipyramids will interact with the first- and/or second-neighbor Te atoms, resulting in the three-dimensional continuous random network even in tellurite glasses with over 30 molu200a% of alkali oxides.

Preparation of branched-polyfluoroalkylsilane-coated silica gel columns and their HPLC separation characteristics

SummaryThe conditions for reaction of the branched polyfluoroalkylsilane D3CL with silica gel have been examined. From elemental analyses and29Si NMR spectra it was found that the surface coverage and endcapping of D3CL-coated silica gel (Fluofix®) were the same as for ODS packings.The separation behavior of these phases was compared that of a variety of other packings. For polyaromatic compounds and benzene derivatives Fluofix worked in the reversed-phase mode and its retention characteristics were similar to those of C1 or CN packings. For fluorinated compound the retention characteristics of the phases is similar to those of ODS although with MeOH-water and MeCN-water mobile phases the pressure loss was lower for the fluorinated phases than for ODS.

Structure and vibrational properties of alkali phosphate glasses from ab initio molecular orbital calculations

Abstract We have carried out ab initio molecular orbital calculations on clusters of atoms modeling the local structure of lithium and sodium metaphosphate glasses to investigate their structure and vibrational properties. The optimized structural parameters and O 1s photoelectron energies calculated at the Hartree–Fock/3-21G* level are in good agreement with the observed ones. We then performed frequency calculations for the lithium metaphosphate cluster. The calculated Raman spectrum agrees with the experimental one. On the basis of the calculated results, we interpret the vibrational spectra of alkali phosphate glasses and discuss the local coordination environments of alkali cations in the glassy system.