TeO4 Trigonal Bipyramid Research Articles

Poling temperature dependence of optical second-harmonic intensity of MgO–ZnO–TeO2 glasses

Poling temperature variation of optical second-harmonic intensity induced by electrical poling has been examined for 30ZnO⋅70TeO2, 5MgO⋅25ZnO⋅70TeO2, and 10MgO⋅20ZnO⋅70TeO2 glasses. The Maker fringe pattern of these glasses indicates that the orientation of electric dipoles presumably due to TeO4 trigonal bipyramids and TeO3 trigonal pyramids is not restricted within the glass surface but extends into the inside of bulk glass. The poling temperature dependence of second-harmonic intensity manifests a maximum in all the glasses. There exists a tendency that the poling temperature which corresponds to the maximum of second-harmonic intensity is higher in the glass with higher glass transition temperature. This fact suggests that the orientation of tellurite structural units occurs as a result of the structural relaxation of tellurite network at around the glass transition temperature.

Preparation and characterisation of high refractive index PbO–TiO2–TeO2glass systems

We describe the preparation and characterisation of high refractive index PbO–TiO2–TeO2 glass systems. Highly homogeneous glasses were obtained by agitating the oxide mixture during the melting process in an alumina crucible. The characterisation was performed by X-ray diffraction, density, dilatometry, Raman scattering, light absorption and linear refractive index measurements. The results show a change in the glass structure as the PbO content increases: the TeO4 trigonal bipyramids characteristic of TeO2 glasses transform into TeO3 trigonal pyramids. However, the measured refractive indices are almost independent of the glass composition. We show that third-order non-linear optical susceptibilities calculated from the measured refractive indices using Lines' theoretical model are also independent of the glass composition.

Structural study of MoO3TeO2 glasses

MoO3TeO2 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 TeO4 trigonal bipyramids, TeO3+1 polyhedra and MoO6 octahedra as basic structural units. Glasses having low MoO3 content contain MoO6 octahedra having two Mo  O bonds. As MoO3 content increases, the fraction of Mo  O bonds to Mo6+ decreases. When MoO3 content reaches 30–40 mol%, the structure of glasses shows close resemblance to that of MoTe2O7 crystal. On the basis of local structural difference around second-component atoms between MoO3-TeO2 and WO3-TeO2 glasses, differences in the properties of both glasses are discussed.

Second harmonic generation in electrically poled Li2ONb2O5TeO2 glasses

Optical second harmonic generation has been observed in electrically poled Li2ONb2O5TeO2 glasses. Electrical poling was performed at 250°C for 30 min under an applied dc potential of 3–4 kV. Second harmonic generation takes place in binary Li2OTeO2 and Nb2O5TeO2 glasses as well as ternary 10Li2O · 10Nb2O5 · 80TeO2 and 15Li2O · 15Nb2O5 · 70TeO2 glasses as previously reported. The observation of second harmonic generation in tellurite glasses which do not contain Li+ ions leads to speculation that the second harmonic generation is not attributed to the Li+ ion migration but is presumably ascribed to a long-range orientation of electric dipoles due to asymmetrical structural units, i.e., TeO4 trigonal bipyramids and TeO3 trigonal pyramids.

EXAFS and RDF studies of TeO2–Li2O glasses

Local arrangements around Te atoms in TeO2-Li2O glasses with four different Li2O contents (15, 20, 25, and 30 mol %) are observed by Te K EXAFS spectroscopy and x-ray diffraction by making use of synchrotron radiation. EXAFS results based on the two-shell fitting method indicate that interatomic distances of Te-O in axial (ax) sites decrease from 0.208 to 0.197 nm with increasing Li2O contents, while distances between tellurium atom and oxygen atoms in equatorial (eq) sites change slightly from 0.190 to 0.188 nm. Total coordination numbers seem to decrease slightly with increasing Li2O contents. These results suggest the coordination states of tellurium atoms are changed from TeO4 trigonal bipyramids to TeO3+1 polyhedra and TeO3 trigonal pyramids. RDF results also suggest the change of coordination states of tellurium atoms. TeO3+1 polyhedra in glasses are considered to be connected at the vertices with Te-eq Oax-Te or Te-ax Oax-Te linkage as seen in crystalline α-Li2Te2O5.

特集 光機能材料 希土類含有テルル酸ガラスのアップコンバージョン発光特性

Ternary tellurite glasses were prepared by a conventional quenching method in the system TeO2-LiO0.5-YO1.5⋅IR spectra reveal that the glasses contain the following polyhedra: deformed TeO6 groups, TeO4-trigonal bipyramids, TeO3-trigonal pyramids, or combinations of these polyhedra. The highly addition of glass-network modifiers, especially Li+ ion, leads to a collapse of polyhedra networks. The intense emission peak, due to the transition 4S3/2-4I15/2' was found at 546 nm in tellurite glasses doped with Er3+ under 378 nm and 973 nm excitations at the room temperature. Upon excitation at 973nm, the emission shows a typical upconversion characteristic, indicating the quadratic profiles of the emission intensities against the exciting powers. The emission intensities tend to be dependent upon 378nm excitation, but independent of Er3+ concentration upon 973 nm excitation. The excitation and emission involve two photons process through the 4I11/2 level of Er3+ ion. Up conversion fluorescence is, also, enhanced at 547nm by the supplementary doping with Yb3+ ion.

Phase Separation of Phosphotellurite Glass Investigated by 57Fe-Mössbauer Spectroscopy and DTA

Abstract The isomer shifts (δ) of xP2O5·(95−x)TeO2·5Fe2O3 glasses (x = 0–28), 0.38–0.39 mm s−1, suggest that Fe3+ substitutes for Te4+ of TeO4 trigonal bipyramids. The δ’s of 0.42–0.43 mm s−1 obtained when 30 ≤ x ≤ 40 indicate that Fe3+ (Oh) is present at interstitial sites of PO4 tetrahedra in the phosphate-rich phase.

Structural Change of the IR-Transmitting Tellurite, Gallate and Aluminate Glasses Caused by the 60Co-Gamma Ray Irradiation

The 57Fe-Mössbauer parameters of γ-ray irradiated xK2O·(95-x)TeO2·5Fe2O3 (x=5, 25), xMgO·(95-x)TeO2·5Fe2O3 (x=5, 25) and 95TeO2·5Fe2O3 glasses suggest a cleavage of Te(Fe)-O-Te bond and an increase of the symmetry of Te(Fe)O4 trigonal bipyramids. There is a linear relationship between the resultant Tg and the quadrupole splitting (Δ), obeying the “Tg-Δ rule”. A cleavage of Ga(Fe)-O-Ga bond and an increased symmetry of Ga(Fe)O4 tetrahedra are found in the irradiated 50CaO·40Ga2O3·10Fe2O3 glass. The X-ray diffraction and FT-IR absorption spectra indicate the precipitation of Ga2O3 and CaO phases, and a marked decrease of transmittance is observed in the FT-IR transmission spectra. On the contrary, gamma-ray irradiated xCaO·(95-x)Al2O3·5Fe2O3 glasses (x=55∼60) show little change in the structure nor the IR transparency.

Correlation between the structure and glass transition temperature of potassium, magnesium and barium tellurite glasses

The Mossbauer spectrum of tellurite glasses, containing 5 mol% Fe2O3 as a probe, consists of a paramagnetic quadrupole doublet with an isomer shift of 0.39 ± 0.01 mmsec−1. This indicates that Fe3+ ions are present at substitutional sites of Te4+ ions constituting distorted TeO4 trigonal bipyramids, each of which has one oxygen vacancy at an equatorial site. On increasing the K2O content from O to 35 mol%, the quadrupole splitting (Λ) for potassium tellurite glasses decreases continuously from 0.76 to 0.44 mm sec−1. On the other hand, Λ for magnesium and barium tellurite glasses increases with increasing MgO and BaO content, respectively. When the alkali or alkaline earth oxide contents are the same as each other, Λ increases in proportion to the ionic potential (Z/r) of the alkali or alkaline earth metal ion. These results suggest that the glass matrices of alkaliv and alkaline earth tellurite glasses are continuously changed into a chain and a three-dimensional network structure, respectively. Differential thermal analysis studies reveal that there exists a linear relationship between the glass transition temperatureT g and the quadrupole splitting, indicating thatT g is primarily determined by the magnitude of the distortion of TeO4 trigonal bipyramids. This relationship is also applicable to several oxide glasses.

ChemInform Abstract: Structural Study of Na2O‐TeO2 Glasses by Moessbauer Spectroscopy and Differential Thermal Analysis.

AbstractThe Moessbauer spectra of a series of Na2O/TeO2 glasses containing 5 mol% Fe2O3 indicate that Fe3+ ions are present at the Te4+ sites in distorted TeO4 trigonal bipyramids.

Normal Vibrations of Two Polymorphic forms of TeO<sub>2</sub> Crystals and Assignments of Raman Peaks of Pure TeO<sub>2</sub> Glass

Raman spectra of paratellurite, tellurite and pure TeO2 glass were measured. The normal vibration of paratellurite and tellurite was analyzed. The spectrum of pure TeO2 glass were deconvoluted into symmetric Gaussian functions. The normal vibrations of paratellurite are exactly described as combined representations of movement of oxygen atom in Te-eqOax-Te linkage and vibrations of TeO4 trigonal bipyramid (tbp). Compared the resolved Raman peaks of pure TeO2 glass with normal vibration of paratellurite, all Raman peaks from 420 to 880cm-1 are assigned to the vibrations of TeO4 tbp and Te-eqOax-Te linkage. The antisymmetric stretching vibrations of Te-eqOax-Te linkage have relatively large intensities to symmetric stretching vibrations of Te-eqOax-Te linkage. In pure TeO2 glass, TeO4 tbps are formed by most of tellurium atoms and connected at vertices by the Te-eqOax-Te linkages.

Structural Study of Na2O–TeO2 Glasses by Mössbauer Spectroscopy and Differential Thermal Analysis

Abstract A Mössbauer spectrum of xNa2O·(95−x)TeO2·5Fe2O3 glasses (0≤x≤35) consists of a paramagnetic quadrupole doublet peak with an isomer shift of 0.39±0.01 mm s−1 with respect to metallic iron. Quadrupole splitting of the doublet peak changes gradually from 0.76 to 0.60 mm s−1 when Na2O content is changed from 0 to 35 mol% at 5 mol% intervals. These results suggest that Fe3+ ions are present at substitutional sites of Te4+ ions constituting distorted TeO4 trigonal bipyramids. Each of the distorted TeO4 trigonal bipyramids has an oxygen vacancy and a lone electron pair at one of the equatorial sites. Decreased quadrupole splitting is ascribed to an increased symmetry of FeO4 (and also TeO4) trigonal bipyramids, due to a formation of nonbridging oxygen atoms followed by a gradual change of the glass matrix from a two-(β-TeO2) or three-(α-TeO2) dimensional network structure to a lower dimensional network structure. These structural changes are also deduced from a composition dependency of glass transition temperatures (Tg), which decrease continuously from 318 to 232 °C with increasing Na2O content.

Structure and ionic conductivity of LiCl-Li2O-TeO2 glasses

The structure and the ionic conductivity of the ternary LiCl-Li2O-TeO2 glasses were investigated. The structure was studied mainly by means of IR spectroscopy. It was observed that the Te-Oax bond, where ax stands axial position of the TeO4 trigonal bipyramid, became weaker with increasing the LiCl content in binary LiCl-TeO2 glasses, indicating that LiCl works as a network modifier. On the other hand, the gradual increase in the wave number of the peak due to the Te-Oax bond was observed when Li2O was replaced with LiCl. This was explained in terms of a difference in bonding characteristics between Te-Oeq and Te-Cleq bonds, where eq denotes the equatorial position.The electrical conductivity of the glasses with a high concentration of Li+ ion reached an order of 10−6 S cm−1 at 25° C. This value was comparable to those of the other fast Li+ ion conducting glasses such as LiCl-Li2O-B2O3 and LiPO3-LiCl systems. The composition dependence of the electrical conductivity was discussed in relation to the glass structure, especially in terms of bonding characteristics of Te-Cl and Te-O.

IR spectra and structures of tellurite glasses

It is shown with IR spectral investigations that the short range order of certain tellurite glasses, obtained from monomineral crystalline phases, is similar to that of the crystals. They may contain the following polyhedra: TeO4-trigonal bipyramids (C2v symmetry), deformed TeO4 groups, TeO3 trigonal pyramids (C3v point symmetry), or combinations of these polyhedra. The introduction of V2O5 and MoO3 in the binary glasses leads to a TeO4 → TeO3 transition. MoO3 delays the decay of TeO4 groups in a wider concentration range.