Compositional dependence of infrared absorption spectra studies for TeO2-P2O5 and TeO2-P2O5-Bi2O3 glasses

The infrared absorption spectra of the vitreous TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ systems are studied in the spectral region of 4000 to 200 cm^–1. Absorption bands in this range are assigned. The midband wavenumber and the absorption intensity for the attributed bands are found to be strongly and systematically dependent on glass composition. Quantitative analysis was also attempted to justify our attribution of the observed bands.     

Optical absorption studies for TeO2-P2O5 and Bi2O3-TeO2-P2O5 glasses

A range of TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ glass systems were prepared. The optical absorption spectra were measured in the spectral range 300–800 nm and it was found that the fundamental absorption of these glasses is dependent on the glass composition. The optical energy gap of binary glasses increases with increasing TeO₂ content while the addition of Bi₂O₃ to TeO₂-P₂O₅ decreases the optical energy gap. The absorption edges of these glasses arise from direct forbidden transitions and occur at photon energies in the range of 2.17 to 2.97 eV for TeO₂-P₂O₅ glasses and 2.63 to 2.32 eV for Bi₂O₃-TeO₂-P₂O₅ glasses depending on their composition.     

Phase equilibria and immiscibility in the TeO2-P2O5 system

The phase equilibria and immiscibility of mutual glass formers up to 50 mol% P₂O₅ have been studied. Phase analysis indicates the formation of three new phases — incongruent melting Te₄P₂O₁₃, Te₂P₂O₉, and a supposed metacompound. Electron microscope investigations established stable and metastable phase separation. The immiscibility confines the tendency to glass formation up to 25.8 mol % P₂O₅. A reliable interpretation in relation to the morphology of liquid-liquid immiscibility and crystallization is considered.     

Non-isothermal kinetic studies for binary TeO2-P2O5 glass system

A study of TeO₂–P₂O₅ glass system has been carried out by Differential Thermal Analysis (DTA) to elucidate the kinetics of crystallization for these glassy samples. The results of DTA performed at different heating rates are discussed. The values of the glass transition temperature, T _g , as well as the glass crystallization temperature, T _c , are found to be dependent upon the heating rate. From this dependence, the values of activation energy for both the glass transition and crystallization are evaluated and discussed     

A.c. conductivity for amorphous TeO2-P2O5 glass system

The a.c. conductivity for the TeO₂-P₂O₅ glassy system was measured in the temperature range 300–573 K and in the frequency range 100 Hz to 10 kHz. The a.c. conductivity () increased with frequency according to the relation ()^s. The frequency exponent s was found to decrease with increasing temperature. The composition dependence of the conductivity was also investigated. The density of states was also calculated using the Elliott model. The a.c. conductivity increased over the studied temperature range. The obtained experimental data have been analysed with reference to various theoretical models. The analysis shows that the correlated barrier hopping (CBH) model is the most appropriate mechanism for conduction in the TeO₂-P₂O₅ glass system.     

The crystallisation of glasses from the ternary CaF2-CaAl2Si2O8-P2O5 system

A study of glasses from the ternary system CaF₂-CaAl₂Si₂O₈-P₂O₅ has been carried out. It has been shown that glasses with low phosphorus contents and high fluorite contents crystallise to fluorite. Fluorine reduces the glass transition temperature and is also required for the formation of fluorapatite (FAP). In the absence of fluorine in the glass no apatite phase is formed. Bulk nucleation of FAP is favoured for glasses with Ca:P ratios close to the apatite stoichiometry of 1.67 and with low crosslink densities. Thermal gravimetric analysis showed significant weight losses attributable to the formation of volatile silicon tetrafluoride to occur on crystallisation of the aluminium containing phases, anorthite and mullite, which supports the view that silicon tetrafluoride formation is hindered by fluorine bonding to the aluminium atoms of the glass network. Anorthite crystallisation always occurred by a surface nucleation mechanism and appeared to be favoured by the higher silicon to aluminium ratio in these glasses compared to previously studied glass compositions.     

Infra-red spectra of crystalline phases and related glasses in the TeO2-V2O5-Me2O system

The crystal line phases Me₂O·V₂O₅·2TeO₂ (Me=Li, Na, K, Cs, Ag) and their glasses are studied with the aid of infra-red spectroscopy. The radial distribution function (RDF) curves of two glasses, Na₂O·V₂O₅·2TeO₂ and Cs₂O·V₂O₅·2TeO₂, are obtained by an X-ray diffraction study. An attempt is made to identify the main bands in the infra-red spectra of the crystalline compounds and the glasses. The absorption bands in the 970 to 880 cm^–1 range are assigned to the stretching modes of the VO₂ isolated groups. A trend is observed towards a shift of the high-frequency band by the replacement of an alkaline ion with another in the order Ag⁺, Cu⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, which is explained by their different polarizing ability. With the aid of X-ray diffraction studies it is shown that the basic structure units in the glasses studied are the VO₄ and TeO₄ groups.     

Novel low-temperature synthesis of glasses and glass-ceramics in the B2O3-SiO2-P2O5 system

In recent years considerable progress has been made in electronic packaging substrate technology. The future need of miniaturization of devices to increase the signal processing speed calls for an increase in the device density requiring the substrates to be designed for better thermal, mechanical and electrical efficiency. Fast signal propagation with minimum delay requires the substrate to possess very low dielectric constant. Several glasses and glassceramic materials have been identified over the years which show good promise as candidate substrate materials. Among these, borophosphate and borophosphosilicate glass-ceramics have been recently identified to have the lowest dielectric constant (3.8). Sol-gel processing has been used to synthesize borosilicate, borophosphosilicate and borophosphate glasses and glass-ceramics using inexpensive boron oxide and phosphorus pentoxide precursors. Preliminary results of the processing of these gels and the effect of volatility of boron alkoxide and its modification on the gel structure are described. X-ray diffraction, differential thermal analysis and Fourier transform-infrared spectroscopy have been used to characterize the as-as-prepared and heat-treated gels.     

Conduction mechanism at high electric field and switching phenomena in V2O5-P2O5 and V2O5-P2O5-TeO2 glasses

A previous investigation [1] suggests that the conduction in some vanadate glasses is ohmic up to a field of the order of 10⁵ V cm^–1 with an activation energy range from 0.31 to 0.48 eV depending on composition, but independent of temperature above room temperature. In this work the electrical conductivity of these glasses at high electric field is reported. The results suggest that above a field of 4×10⁵ V cm^–1 conduction becomes non-ohmic, and this is found to be due to lowering the potential barrier to the carrier at high electric field. Memory switching is observed in thin blown film samples of both binary and ternary glass systems, and is associated with field-induced crystallization of a localized region and the formation of a conduction channel in the switched area due to a self-heating effect.     

Phase equilibrium,glass-forming,properties and structure of glasses in the TeO2-B2O3 system

Phase equilibrium, glass-forming, properties and structure of the glasses in the TeO₂-B₂O₃ system have been investigated. The phase diagram is a simple eutectic-like type without any compound formation. A wide region of stable phase separation has been established. A monotectic temperature at 934 K and nonvariant point at 73.6% TeO₂ has been determined. The temperature dependence of the stable phase separation in the system has been studied. Some properties (density, transformation temperature, softening point, coefficient of thermal expansion, hardness, absorption in the UV and VIS region) of the tellurite borate glasses have been investigated. A structural interpretation of the glasses, on the basis of B¹¹ NMR spectra was undertaken and two coordination states of boron atoms have been established. A simple model of two tellurium-boron-oxygen building units is presented.     

EPR and magnetic susceptibility studies on V2 O5-P2O5-PbO glasses

EPR and magnetic susceptibility investigations on the glass system with 04+ ion content are explained using a simulation program on the assumption of the superposition of two signals, one with hyperfine structure (hfs) typical for isolated ions and another one consisting of a broad line without hfs characteristic for clustered ions. The hfs is not shown for x<3mol%V₂O₅. The EPR data show the presence of V₄₊ ions in a square-pyramidal co-ordination (C_4V) for 3x20mol%V₂O₅. The progressive disappearance of hfs for high V²O⁵ content (>20 mol %) suggests the increase of the associated ion number coupled by superexchange interactions. This result is consistent with magnetic susceptibility data for >3 mol % where the temperature dependence of magnetic susceptibility is described by the Curie–Weiss type law with a negative paramagnetic Curie temperature. The magnetic susceptibility results allowed the estimation of the V⁴⁺/V⁴⁺ + V⁵⁺ ratio in the sample studied.     

掺铒TeO2-Nb2O5-ZnO系统玻璃的上转换发光性能

稀土离子掺杂碲酸盐系统玻璃是一类应用前景良好的上转换发光材料.研究了含铒TeO2-Nb2O5-ZnO系统玻璃在980nm抽运下的上转换光谱,结果发现存在3个上转换荧光谱带,分别对应于2H11/2→4I15/2、4S3/2→4I15/2和4F9/2→4I15/2,而且Er3 含量的增加可明显提高材料在530、550和660nm附近的发光性能.少量的ZnO引入既可以大幅提升材料的上转换发光强度,又能保持铌碲酸盐玻璃良好的化学稳定性.材料的发光机制主要是激发态吸收(ESA)和能量转移(ET),最大声子能量的降低是上转换发光增强的主要原因.     

Phase equilibrium in the TeO2-B2O3-V2O5 system

Journal of Materials Science Letters -     

Growth kinetics of spherulitic apatite in some MgO-CaO-SiO2-P2O5 glasses

Crystallization of glasses with compositions (wt%) of 11.2 MgO, 33.3 SiO₂, (55.5–x) CaO, and xP₂O₅ (x=18.3, 16.65, 15.825 and 15.0) resulted in a spherulitic apatite phase with different crystal morphologies. An ellipsoidal morphology was observed for x=18.3, 16.65 and 15.825, and an anomalous morphology was observed for x=15.0. A metastable phase, which was similar in some characteristics to apatite, was also found for x=15.0. The growth kinetics of the spherulitic apatite crystals were investigated to explain the above observations. Both the dendrite arms along the [0001] and [1 1¯20] directions of the apatite crystals showed constant growth rates in each glass. Growth-rate anisotropy was found between these two directions. The ellipsoidal shape of the apatite crystals is explained by this growth-rate anisotropy. The growth rates, and the growth-rate anisotropy, varied with the P₂O₅ content in such a manner that the changes in phase formation behaviour can be explained on the basis of the kinetic results.     

Study of structures and properties of ZnO-Sb2O3-P2O5-Na2O glasses

The influence of ZnO substitution by 0–12 wt.% Na₂O on the properties of ZnO-Sb₂O₃-P₂O₅-Na₂O glasses has been investigated. The structure and properties of the glasses with the composition of (13.86-x)ZnO-57.93Sb₂O₃-28.21P₂O_5?x Na₂O (x = 0–12 wt.%) were characterized by infrared spectra (IR), X-ray diffraction and differential thermal analysis (DTA). The results of IR indicated an increase in the intensity of symmetric vibrations of P-O-P bond, which was confirmed by the improvement of water durability with the increasing amount of Na₂O in the range of 0–10 wt.%. Substitution of 10 wt.% Na₂O led to the weight loss of the glass to 5.93 mg/cm^?2 after immersion in deionized water at 50 °C for 24 h. The results of XRD showed that the ability of crystallization decreased, indicating the good thermal stability of the glass. The glass containing 8 wt.% Na₂O had the best properties in every respect and might be an alternative to lead based glasses for the applications, providing further composition improvement.     

Optical,infrared and electrical conductivity of glasses in the TeO2-B2O3 system

Infrared (IR) and optical absorption spectra were measured in order to study the structure of some tellurite glasses containing boric oxide. The compositions (mol%) were (100-X) TeO₂,XB₂O₃ whereX=5, 10, 20, 25, 30. The optical spectra were measured at room temperature in the wavelength range 350–450 nm, and the results show that the fundamental absorption edge is a function of composition, with the optical absorption due to indirect transitions. The optical band gap increases with increasing B₂O₃ content. The validity of the Urbach rule was investigated. The IR results prove the distribution of the TeO₄ polyhedra which determines the network and the basic oscillations of the building units in the tellurite glasses. The IR results also prove the distribution of the boroxal group. The electrical conductivity was measured as a function of temperature in the temperature range (300–573 K). Both the conductivity and activation energy were found to be a function of added oxide type.