Jisun Jin

Neutron and X-ray diffraction studies of PbOGa2O3 and Bi2O3Ga2O3 glasses

Abstract The structure of 50PbO·50GaO1.5 and 80BiO1.5·20GaO1.5 glasses was investigated by neutron and X-ray diffraction. Most Ga3+ ions are four-coordinated in both glasses. PbO3 trigonal pyramids and PbO4 square pyramids are present in 50PbO·50GaO1.5 glass. The stronger glass-forming ability in PbOGaO1.5 is attributed to (PbO3, PbO4)n infinite spiral chains as in crystalline PbSiO3. Bi3+ ions form BiO5 and BiO6 units in 80BiO1.5·20GaO1.5 glass as in α-Bi2O3. This glass may be constructed by (BiO5, BiO6)n layers and GaO33− chains. It is assumed that in these glasses nearly all oxygen atoms bonded to Pb2+ or Bi3+ ions are three- or four-coordinated and most oxygen atoms bonded to Ga3+ ions are three-coordinated. It is found that the structure of the present ‘non-conventional’ glasses are contrary to Zachariasens rules for glass formation.

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 mol % of alkali oxides.

Neutron diffraction and solid-state MAS-NMR studies of the structure of Y-AI-Si-O-N oxynitride glasses

Abstract Neutron diffraction and magic angle spinning (MAS) 27Al and 29Si NMR have been applied to study the local structure of glasses in the system Y-Al-Si-O with and without addition of AlN. 27Al MAS NMR indicated that in the Y-Al-Si-O-N oxynitride glass there is no Al-N bonding and aluminium atoms occupy various sites within the glass structure. The first peak of the radial distribution function curves obtained by neutron diffraction was deconvoluted into four peaks which are attributable to Si-O, Si-N(Al-O(4)), Al-O(5) and Al-O(6) pairs and the coordination numbers of Si, N, Al and Y were estimated. The glass network is assumed to consist mainly of corner-sharing AlO4 tetrahedra and SiO3N tetrahedra. 86% of N atoms are three-coordinated and 14% of N atoms are two-coordinated in the present oxynitride glass.

Preparation and Properties of CuSr2(YxCa1-x)Cu2Oy and Cu(SrzCa1-z)2YCu2Oy

We tried to synthesize high pressure Cu system superconductors at mild conditions. For the this purpose, the sol-gel method was applied. The best conditions for obtain target materials were discussed.

Preparation of Superconducting Oxide by Sol-Gel Method

Superconducting YBa2Cu3O7-x fibers and coating films have been prepared using solgel method. Homogeneous viscous sol was prepared by concentrating an aqueous solution of metal acetates. Gel fibers of 5μm - 2 mm in diameter and of more than 50 cm in length could be drawn from the sol. Heat-treated fibers had a hollow structure and were fragile, but showed superconductivity of Tc(end) at 73 K. For preparation of YBa2Cu3O7-x coating films, metal alkoxide solution was prepared using triethanolamine to dissolve copper alkoxide. Repeated application of the solution on a zirconia substrate and heat treatment in O2 resulted in the formation of a superconducting coating film of 1.5 μm in thickness having Tc(end) at 56 K. Factors affecting the properties of the fibers and coating films have been discussed.