Shinichi Sakida

Part 2.125Te NMR study of M2O-TeO2 (M = Li, Na, K, Rb and Cs) glasses

Abstract The structure of TeO 2 and M 2 O–TeO 2 (M=Li, Na, K, Rb and Cs) glasses has been investigated by means of 125 Te static and magic-angle spinning (MAS) NMR spectroscopies. On the basis of the relationship between the local structures around Te atoms and the NMR parameters obtained by 125 Te NMR spectra of various tellurite crystals, the local structures around Te atoms in TeO 2 and M 2 O–TeO 2 glasses were examined. The spectral simulation of static NMR spectra enabled us to discriminate between TeO 3 trigonal pyramid (tp) and TeO 4 trigonal bipyramid (tbp) and to estimate the fractions of TeO 3 tp (N 3 ) and TeO 4 tbp (N 4 ). It was concluded that in TeO 2 glass TeO 4 tbps are connected by sharing their corners as in α-TeO 2 crystal. N 3 increased and N 4 decreased with increasing M 2 O content. On the basis of a previous structural model, the fractions of TeO 4 tbp without a non-bridging oxygen (NBO) atom, TeO 4 tbp with an NBO atom, and TeO 3 tp with two NBO atoms were calculated. A new model which presents the structural change for M 2 O–TeO 2 glasses has been proposed.

Part 1. 125Te NMR study of tellurite crystals

Abstract 125 Te static and magic-angle spinning (MAS) NMR spectra of tellurite crystals with known crystal structures have been measured to determine the isotropic chemical shift δ iso , the chemical shift anisotropy Δ δ and the asymmetry parameter η . On the basis of structural unit, tellurite crystals are classified for convenience into TeO 3 type (isolated TeO 3 and terminal TeO 3 type), TeO 3+1 type and TeO 4 type (α-TeO 2 and β-TeO 2 type). As a result, the following relations were found: TeO 3 ⩾TeO 3+1 xa0≈xa0β-TeO 2 xa0>xa0α-TeO 2 in δ iso(MAS) , β-TeO 2 ⩾α-TeO 2 xa0>xa0TeO 3+1 xa0>xa0terminal TeO 3 ⩾isolated TeO 3 in |Δ δ | and TeO 4 ⩾TeO 3+1 ⩾TeO 3 in η . It was also found that the combination of |Δ δ | and η , namely, the relative values of δ 1 , δ 2 and δ 3 , can elucidate the local structure around Te atoms more definitely than δ iso . This diagram is useful for examining the structures of tellurite crystals and glasses. (Glasses are discussed in another paper.)

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.

125Te and 51V static NMR study of V2O5-TeO2 glasses

The structures of V2 O5 -TeO2 glasses are investigated by means of 125 Te and 51 V static NMR spectroscopies and the local structures around the Te and V atoms are discussed in detail from the respective NMR spectra. The fraction of TeO3 trigonal pyramids increases and that of TeO4 trigonal bipyramids decreases with increasing V2 O5 content. The structures of V2 O5 -TeO2 glasses are quite different from those of tellurite glasses containing network-modifying oxides. The fraction of VO4 tetrahedra increases and that of VO5 trigonal bipyramids decreases with increasing V2 O5 content. Both chains consisting of tellurite structural units and those consisting of vanadate structural units contribute to the formation of the glass network in V2 O5 -TeO2 glasses.