No abstract

The structure of pure TeO 2 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 TeO 4 trigonal bipyramids to more regular TeO 3 trigonal pyramids with increasing alkali content. It has also been shown that the TeO 3 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 ͑NBO͒ atoms in tellurite glasses do not exist in their ''pure'' form; that is, all the NBO atoms in TeO 3 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.

L@³@ËÒae¿ÅáZ_ §åµOìÌ OP(OSiMe 3 ) x (OH) 3|x m¬ Vc¡÷E´ëpEàì²iE¡örM såw»w¤³@fÞ»w¤åÞC6110011 s{F¡sÜT he synthesis of organicinorganic hybrid precursors for lowmelting glass has been proposed. In this process, a nonaqueous acidbase reaction of POH{SiCl¨POSi{HClª was employed using or thophosphoric acid (H 3 PO 4 ) and trimethylchlorosilane (Me 3 SiCl) as starting materials. The formation of POSiMe 3 linkage and the disappearance of POH group were conrmed by 29 Si and 31 P NMR spectra. The viscosity decrease of the precursors observed at high Si concentrations was caused by the decrease in the number of POH, which was correlated to the decrease of the hydrogen bond. By the use of POSiMe 3 link age, lowmelting glasses in the system of Me 3 SiO 0.5 Me 2 SiOSnOP 2 O 5 have also been prepared through the nonaqueous acidbase reaction. The hybrid glasses thus obtained exhibited low glass transition tempera tures, which changed from 29 to |47 C as the SiMe 3 content increased. Termination of the oxide frame work by the organic functional groups lowered the network dimension, giving rise to the lower glass transi tion temperature.