Norio Mochida

Raman spectra of MO1/2TeO2 (M = Li, Na, K, Rb, Cs and Tl) glasses

The structure of MO 1/2 TeO 2 (M = Li, Na, K, Rb, Cs and Tl) binary glasses has been studied by means of Raman spectroscopy. The glasses having low alkali content have a continuous network constructed by sharing corners of TeO 4 trigonal bipyramids (tbps) and TeO 3 + 1 polyhedra having one non-bridging oxygen atom (NBO). In the glasses containing 20–30 mol% alkali oxide, TeO 3 trigonal pyramids (tps) having NBOs are formed in the continuous network. When alkali content exceeds 30 mol%, isolated structural units, such as Te 2 O 2− 5 ion, coexist in the continuous network. The fraction of TeO 4 tbps decreases with increasing alkali content. The glasses, which contain nearly 50 mol% alkali oxide, are composed of a continuous network constituted by TeO 3 + 1 polyhedra and TeO 3 tps, and of isolated structural units, such as Te 2 O 2− 5 and TeO 2− 3 ions. The structure of thallium tellurite glasses having less than 30 mol% TlO 1/2 is similar to that of alkali tellurite glasses containing equal amounts of MO 1/2 . The fraction of TeO 3 tps having NBOs in the thallium tellurite glasses, when TlO 1/2 content is equal to or higher than 40 mol%, is larger than that in the corresponding alkali tellurite glasses. In the 66TlO 1/2 ·34TeO 2 glass, most of tellurium atoms are in a form of isolated TeO 2− 3 ion. A new hypothesis is also given for a mechanism for the basic structural changes in the tellurite glasses.

Raman spectra of MOTeO2 (M = Mg, Sr, Ba and Zn) glasses

Abstract The structure of MOTeO 2 (M = Mg, Sr, Ba and Zn) glasses was investigated by Raman spectroscopy. The glasses with low BaO have a continuous network constructed by sharing corners of TeO 4 trigonal bipyramids and TeO 3+1 polyhedra having one non-bridging oxygen (NBO) atom. In the glasses, TeO 3 trigonal pyramids having NBO atoms are also formed in the continuous network. In 36BaO · 64TeO 2 glass, isolated structural fragments, such as TeO 3 2− and Te 3 O 8 4− ions, coexist with the continuous network. The structure of MgOTeO 2 glasses is different from that of the BaOTeO 2 glasses. In glasses containing about 40 mol% MgO, a (Te 3 O 8 4− ) n unit, in which n is relatively small, is formed. The fraction of tellurium atoms forming TeO 3 trigonal pyramids increases with MgO content. When MgO exceeds 40 mol%, isolated structural units, such as TeO 3 2− and Te 3 O 8 4− ions, will be formed in glasses. The SrOTeO 2 and ZnOTeO 2 glasses have the same structure as the BaOTeO 2 and MgOTeO 2 glasses, respectively.

Structural study of WO3TeO2 glasses

Abstract Raman spectra of WO3TeO2 glasses and tungstate crystals were investigated. Properties of the glasses such as transition temperature, thermal expansion and density were measured. In the glasses, most tellurium atoms form TeO4 trigonal bipyramids and WO bonds are present. The glasses contain clusters composed of corner-shared WO6 octahedra. An increase in WO3 content promotes the growth of clusters. The coordination state of W6+ having a WO bond is discussed on the basis of crystal chemistry. Tungsten coordination polyhedra occupying the interface of the cluster have a WO bond.

Raman spectra of binary tellurite glasses containing tri- or tetra-valent cations

Abstract Glass formation and structure are investigated in binary tellurite systems containing YO 3/2 , InO 3/2 , LaO 3/2 , ZrO 2 , SnO 2 , HfO 2 , and ThO 2 as second components. No glasses are obtained in two systems, ZrO 2 -TeO 2 and SnO 2 -TeO 2 , because of the precipitation of ZrTe 3 O 8 and SnTe 3 O 8 crystals. Raman spectra and glass properties, such as transition temperature, thermal expansion and density, were measured. Glasses having low LaO 3/2 content have a continuous network structure composed of corner-sharing TeO 4 trigonal bipyramids and TeO 3+1 polyhedra having one non-bridging oxygen atom. Further increase of LaO 3/2 content accelerates a conversion of TeO 4 trigonal bipyramids and TeO 3+1 polyhedra into TeO 3 trigonal pyramids having two or three non-bridging oxygen atoms. In the YO 3/2 -TeO 2 and ThO 2 -TeO 2 systems, the change of glass structure follows the same process as in LaO 3/2 -TeO 2 glasses. In 23InO 3/2 · 77TeO 2 glass, few structural fragments composed of TeO 3 trigonal pyramids are formed. There is a possibility that 5HfO 2 · 95TeO 2 glass contains a small fraction of structural fragments present in HfTe 3 O 8 crystal.

Structural study of MoO3TeO2 glasses

Abstract MoO 3 TeO 2 glasses were investigated by Raman spectroscopy and differential thermal analysis, and transition temperature, thermal expansion and density were measured. Mo  O bonds are present in the entire glass composition. The glasses contain TeO 4 trigonal bipyramids, TeO 3+1 polyhedra and MoO 6 octahedra as basic structural units. Glasses having low MoO 3 content contain MoO 6 octahedra having two Mo  O bonds. As MoO 3 content increases, the fraction of Mo  O bonds to Mo 6+ decreases. When MoO 3 content reaches 30–40 mol%, the structure of glasses shows close resemblance to that of MoTe 2 O 7 crystal. On the basis of local structural difference around second-component atoms between MoO 3 -TeO 2 and WO 3 -TeO 2 glasses, differences in the properties of both glasses are discussed.

Raman spectra of BO32TeO2 glasses

Abstract The structure of BO 3 2  TeO 2 glasses was investigated by Raman spectroscopy. Glasses with low BO 3 2 content have a continuous network structure composed mainly of TeO4 trigonal bipyramids. In the network, a considerable fraction of boron atoms form BO4 groups and a small fraction of boron atoms form B2O5 and BO3 groups. With increase of BO 3 2 content, both trigonally coordinated tellurium and tetrahedrally coordinated boron atoms are increased in numbers. Condensed borate groups are formed by condensation of BO4, B2O5 and BO3 groups. In glasses containing nearly 50 mol% BO 3 2 , a continuous network is constituted by tellurite clusters, B2O5, BO3, BO4 and condensed borate groups. The behavior of boron in the BO 3 2  TeO 2 system is discussed on the basis of TeO and BO bond strengths.

Raman spectra of BO 3 2 TeO 2 glasses

Abstract The structure of BO 3 2  TeO 2 glasses was investigated by Raman spectroscopy. Glasses with low BO 3 2 content have a continuous network structure composed mainly of TeO4 trigonal bipyramids. In the network, a considerable fraction of boron atoms form BO4 groups and a small fraction of boron atoms form B2O5 and BO3 groups. With increase of BO 3 2 content, both trigonally coordinated tellurium and tetrahedrally coordinated boron atoms are increased in numbers. Condensed borate groups are formed by condensation of BO4, B2O5 and BO3 groups. In glasses containing nearly 50 mol% BO 3 2 , a continuous network is constituted by tellurite clusters, B2O5, BO3, BO4 and condensed borate groups. The behavior of boron in the BO 3 2  TeO 2 system is discussed on the basis of TeO and BO bond strengths.

Raman spectra of glasses

Abstract The structure of BO 3 2  TeO 2 glasses was investigated by Raman spectroscopy. Glasses with low BO 3 2 content have a continuous network structure composed mainly of TeO4 trigonal bipyramids. In the network, a considerable fraction of boron atoms form BO4 groups and a small fraction of boron atoms form B2O5 and BO3 groups. With increase of BO 3 2 content, both trigonally coordinated tellurium and tetrahedrally coordinated boron atoms are increased in numbers. Condensed borate groups are formed by condensation of BO4, B2O5 and BO3 groups. In glasses containing nearly 50 mol% BO 3 2 , a continuous network is constituted by tellurite clusters, B2O5, BO3, BO4 and condensed borate groups. The behavior of boron in the BO 3 2  TeO 2 system is discussed on the basis of TeO and BO bond strengths.