Tellurate Glasses Research Articles

FTIR, Raman, and UV-Vis spectroscopic and DFT investigations of the structure of iron–lead–tellurate glasses

In this work, the effects of iron ion intercalations on lead-tellurate glasses were investigated via FTIR, Raman and UV-Vis spectroscopies. This homogeneous glass system has compositions xFe(2)O(3)·(100-x)[4TeO(2)·PbO(2)], where x = 0-60mol%. The presented observations in these mechanisms show that the lead ions have a pronounced affinity towards [TeO(3)] structural units, resulting in the deformation of the Te-O-Te linkages, and leading to the intercalation of [PbO( n )] (n = 3, 4) and [FeO( n )] (n = 4, 6) entities in the [TeO(4)] chain network. The formation of negatively charged [FeO(4)](1-) structural units implies the attraction of Pb(2+) ions in order to compensate for this electrical charge. Upon increasing the Fe(2)O(3) content to 60mol%, the network can accommodate an excess of oxygen through the formation of [FeO(6)] structural units and the conversion of [TeO(4)] into [TeO(3)] structural units. For even higher Fe(2)O(3) contents, Raman spectra indicate a greater degree of depolymerization of the vitreous network than FTIR spectra do. The bands due to the Pb-O bond vibrations are very strongly polarized and the [TeO(4)] structural units convert into [TeO(3)] units via an intermediate coordination stage termed "[TeO(3+1)]" structural units. Our UV-Vis spectroscopic data show two mechanisms: (i) the conversion of the Fe(3+) to Fe(2+) at the same time as the oxidation of Pb(2+) to Pb(+4) ions for samples with low Fe(2)O(3) contents; (ii) when the Fe(2)O(3) content is high (x ≥ 50mol%), the Fe(2+) ions capture positive holes and are transferred to Fe(3+) ions through a photochemical reaction, while the Pb(2+) ions are formed by the reduction of Pb(4+) ions. DFT calculations show that the addition of Fe(2)O(3) to lead-tellurate glasses seems to break the axial Te-O bonds, and the [TeO(4)] structural units are gradually transformed into [TeO(3+1)]- and [TeO(3)]-type polyhedra. Analyzing these data further indicates a gradual conversion of the lead ions from covalent to ionic environment. There is then a charge transfer between the tri- and tetracoordinated tellurium atoms due to the capacity of the lead-tellurate network to form the appropriate coordination environments containing structural units of opposite charge, such as iron ions, [FeO(4)](1-).

The improvement of the amorphous environment of the germanate–tellurate glasses in the presence of the gadolinium ions

Glasses in the system xGd2O3·(100 − x)[TeO2·GeO2] with 0 ≤ x ≤ 50 mol% have been prepared from melt quenching method. In this paper, we investigated changes of the coordination numbers of germanium, tellurium, and gadolinium ions by investigations of FTIR, EPR, and UV–VIS spectroscopy. By analyzing the structural changes resulted from the IR spectra we found that the bending modes of [GeO4] structural units and the deformed modes of the Te–O–Te linkages produce intercalation of the [GdOn] entities in the germanate–tellurate chain network and densification of the glasses by increasing the number of [GeO6] structural units. EPR spectra of the studied samples reveal that the gadolinium ions play a role of network former. The UV–VIS spectra show broad UV absorption bands located in the 250–350 nm region. Their intensity increase with the increasing of Gd2O3 content showing that these stronger transitions can be due to the presence of the O=Ge bonds (n–π* excitations) of [GeO5] structural units. The [GeO5] structural units are more stable thermodynamically than their analogues and the [GeO6] structural units produce the improvement of the amorphous character of these glasses.

Experimental and theoretical investigations on the structure of the lead–vanadate–tellurate unconventional glasses

In this paper, we have examined and analyzed the effects of systematic lead ion intercalations on vanadate–tellurate glasses with interesting results. Glass formation and structural properties of the lead–vanadate–tellurate glasses of compositions xPbO∙(100 − x)[6TeO 2·4V 2O 5], x = 0–100 mol%, are reported for the first time. Influence of lead ions on structural behavior in vanadate–tellurate glasses has been investigated using infrared spectroscopy and DFT calculations. The presented observations in these mechanisms show that the lead ions have an affinity pronounced towards [TeO 3] structural units yielding the deformation of the Te–O–Te linkages and pursuant to the intercalation of [PbO n] entities in the [TeO 4] chain network. On the other hand, lead ions rest between vanadate chains and now directly interact with the oxygen of the V=O bond yielding the elongation of this bond. The role of the lead ions depends on the type of ionic (in the vicinity of the tellurium atoms) or covalent (in the vicinity of the vanadium atoms) bond between lead and oxygen. We propose a possible structural model of building blocks for the formation of continuous random 50PbO·50[6TeO 2·4V 2O 5] glass network. Comparing the theoretical and experimental IR spectral characteristic features, we conclude that the performance of the method/basis sets used on the prediction of the structural data and vibrational modes is good.

Gadolinium-environment in borate–tellurate glass ceramics studied by FTIR and EPR spectroscopy

Modifications of the gadolinium-environment in borate–tellurate glass ceramics system, where 0 ⩽ x ⩽ 30 mol%, under heat treatment have been investigated by FTIR and Electron Paramagnetic Resonance (EPR) spectroscopy. Glass ceramics with a molar composition of xGd 2O 3·(100 − x)[6TeO 2·4B 2O 3] where 0 ⩽ x ⩽ 30 mol%, was prepared by one-step crystallization heat treatment of the parent glass at temperatures of 400 and 475 °C, respectively. After the heat treatment applied at 400 °C, some structural changes were observed and the B 2O 3 crystalline phase appeared in the structure of the samples. The crystallization of the B 2O 3 crystalline phase increases with increasing of the gadolinium concentration because the excess of the oxygen yields the formation of free BO 3 - 3 orthoborate units capable for charge compensation of the gadolinium ions. By increasing of the treatment temperature up to 475 °C, the increase of the capacity of migration inside the glass ceramics network yields the apparition of B 2O 3 and TeO 2 crystalline phases. When a higher Gd 2O 3 content is introduced, more [BO 3] structural units are coupled with gadolinium ions, the Te–O–Te linkages are deformed showing that the Gd 2O 3 behaves as a glass-former by means of the intercalation of [GdO 4] entities in the [TeO 4] chain network. The changes produced by devitrification suggest the competition between cations of tellurium and boron with non-bridging oxygens to compensate the positive charge of the gadolinium ions. Thus, gadolinium ions play a dual role of network former (475 °C) and network modifier (400 °C) in the studied samples

Novel structural properties of the lead–vanadate–tellurate glass ceramics

In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO2·4V2O5], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te2V2 5+O9, Pb3(V5+O4)2, Pb2V2 5+O7, and V2O5-rich amorphous phase. On the other hand, these glass ceramics contain V4+ and V5+ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V4+=O bonds are created by two different mechanisms: the first of reduction of V5+ ions to V4+ ions and thus of creation of V4+=O bonds.

Infrared spectroscopic and DFT investigations of the vanadate–tellurate glasses structures

Vanadate–tellurate vitreous systems with composition (1 − x)TeO 2· xV 2O 5 where x = 0.3 and 0.4 have been prepared by the conventional melt-quench method. The structural aspects have been investigated using FTIR spectroscopy and the density functional theory (DFT) calculations. The present study provides the interesting information concerning devitrification behavior of the vanadate–tellurate vitreous system which occur Te 2V 2O 9 crystalline phase. The structure of the heat-treated glasses was found to consist mainly of rings containing [TeO 3], [TeO 4], [VO 4] and some [VO 5] structural units.

Competitive role of the tellurium and gadolinium cations in structural aspects of the gadolinium–phosphate–tellurate glasses

Abstract Glasses and glass ceramics in the ternary xGd2O3(100 − x)[7TeO2·3P2O5] systems with 0 ≤ x ≤ 70 mol.% have been prepared from melt quenching method. Main results of the quantum–chemical calculation of the structural model for the 7TeO2·3P2O5 glass network show that there is a charge transfer between the tellurium atoms coordinated +3 and +4 and between the tellurium atoms coordinated +4 with the phosphate network. Presence of the multiple cations of gadolinium and tellurium in the glasses to attract the [PO4] structural units for compensation of charge yield a competition between these cations showing the drastic reduction of the characteristic features corresponding to the [PO4] structural units in bandwidth, position and intensity. After the heat treatment applied at 500 °C for 24 h, two crystalline phases appear, namely the Te4P2O13 and GdPO4. The Te4P2O13 crystalline phase is characteristically of the host glass ceramic. The strong affinity of the Gd3+ ions towards the phosphorus groups containing non-bridging oxygen is responsible for the disappearance of Te4P2O13 crystalline phase. The addition of higher Gd2O3 content yields the gradual depolymerization of the phosphate chains and the formation of the GdPO4 crystalline phase.

Structural and electronic properties of tellurite glasses

The structural properties of some tellurite glasses were investigated by FT-IR spectroscopy, density measurements, and quantum chemical calculations. Main results reveal that the ratio TeO4/TeO3 is found to decrease in the order V2O5 > B2O3 > P2O5. For borate–tellurate glasses, the Van Hove singularities corresponding to Te 5s orbital-derived states are cleft suggesting that there are strong tellurium–oxygen interactions. On the other hand, a strong effect of TeO2 on the vitreous B2O3 network is also demonstrated by FT-IR spectrum. This effect yields the apparition of small peaks in the region ranges between 800 and 1600 cm−1 and probably the partial crystallization of the sample. Its spectral features are due to the B–O bond stretching of [BO4] and [BO3] structural units. The quantum chemical data obtained by us show that phosphate–tellurite and vanado–tellurate glasses can behave as semiconductors, whereas borate–tellurite glasses as insulators because the gap between the valence and conduction bands is >3 eV.

The local structure of gadolinium vanadate–tellurate glasses and glass ceramics: Te2V2O9 crystalline phase

Glasses in the system xGd2O3 · (100 − x)[0.7TeO2 · 0.3V2O5] with 0 ≤ x ≤20 mol% have been prepared from melt quenching method. Influence of gadolinium ions on structural behavior in vanadate–tellurate glasses has been investigated using FTIR spectroscopy, X-ray diffraction (XRD), and magnetic susceptibility measurements. The structural changes have been analyzed with increasing rare earth concentration. The structural changes, as recognized by analyzing band shapes of XRD and FTIR spectra, revealed that Gd2O3 causes a higher extent of network polymerization as far as 20 mol%. The structure of the heat-treated glasses was found to consist mainly of the Te2V2O9 crystalline phase. These vitreous systems were investigated by magnetic susceptibility measurements. From the paramagnetic susceptibility χ was calculated at different temperature and from the 1/χ(T) graph, the Curie temperature of the glass has been evaluated. Magnetic susceptibility data show the presence of small antiferromagnetic interactions between the Gd+3 ions.

FTIR spectroscopic and DFT theoretical study on structure of europium–phosphate–tellurate glasses and glass ceramics

Glasses and glass ceramics in the ternary xEu 2O 3·(100 − x)[7TeO 2·3P 2O 5] systems with 0 ⩽ x ⩽ 60 mol% have been prepared from melt quenching method. Influence of europium ions on structural behavior in phosphate–tellurate glasses has been investigated using infrared spectroscopy. The addition of high Eu 2O 3 content resulted in gradual depolymerization of the phosphate chains and formation of the EuPO 4 crystalline phase. Presence of the multiple cations of europium and tellurium in the glasses to attract the [PO 4] structural units for compensation of charge yield a competition between these cations. This preference is decided by the potential of ionization of the cations. The changes of the IR spectral features produced by devitrification suggest that this competition explains the drastic reduction of the characteristic features corresponding to the [PO 4] structural units in bandwidth, position and intensity. After the heat treatment applied at 500 °C for 24 h two crystalline phases appear, namely the Te 4P 2O 13 and EuPO 4. The Te 4P 2O 13 crystalline phase is characteristic of the host glass ceramic. The strong affinity of the Eu +3 ions towards the phosphorus groups containing non-bridging oxygen is responsible for the disappearance of Te 4P 2O 13 crystalline phase. We propose a possible structural model of building blocks for the formation of continuous random 7TeO 2·3P 2O 5 glass network used by density functional theory (DFT) calculations. Comparing the theoretical and experimental IR spectral characteristic features, we conclude that the performance of the method/basis sets used on the prediction of the structural data and vibrational modes is good.

Toward Modeling Phosphate Tellurate Glasses: The Devitrification and Addition of Gadolinium Ions Behavior

Glasses in the xGd2O3 x (100 - x)[7TeO2 x 3P2O5] system with 0 < or = x < or = 20 mol % have been prepared using the melt quenching method. The influence of gadolinium ions on structural behavior of the phosphate tellurate glass has been investigated using infrared spectroscopy and density functional theory (DFT) calculations. The addition of gadolinium ions into the host glass matrix leads to an increase of the glass network polymerization due to the replacement of P-O-P bonds by the more resistant P-O-Te bonds having as result the improvement of the chemical durability of the glass. The structural evolution of the studied glasses with the gradual increase of the gadolinium oxide content up to 20 mol % could be explained by considering that the excess of oxygen may be accommodated by the conversion of some orthophosphate structural units into metaphosphate or/and pyrophosphate units. X-ray diffraction and IR spectra revealed that heat treatment of the samples also causes an increase of the glass network polymerization for heat treatment times, t, up to 36 h, while for 36 h > t > or = 48 h showed a drastic structural modification which lead to the apparition of the Te4P2O13 crystalline phase. DFT calculations show that tellurium atoms occupy two different sites in the proposed model. In the first case the tellurium atom is coordinated with four oxygen atoms giving a trigonal bipyramide arrangement, while in the second case the tellurium atom is coordinated with three O atoms. The calculated IR absorption spectrum of the proposed model for phosphotellurite glasses is in good agreement with the experimental absorption data.

Effect of network modifiers on spectroscopic properties of erbium-doped phosphate glasses

The integrated absorption cross section Σabs, peak emission cross section σemi, Judd-Ofeld intensity parameters Ωt (t=2,4,6), and spontaneous emission probability ArR of Er3+ ions were determined for Erbium doped alkali and alkaline earth phosphate glasses. It is found the compositional dependence of σemi is almost similar to that of Σabs, which is determined by the sum of Ωt(3Ω2 + 10Ω4 + 21Ω6). In addition, the compositional dependence of Ωt was studied in these glass systems. As a result, compared with Ω4 and Ω6, the Ω2 has a stronger compositional dependence on the ionic radius and content of modifiers. The covalency of Er-O bonds in phosphate glass is weaker than that in silicate glass, germanate glass, aluminate glass, and tellurate glass, since Ω6 of phosphate glass is relatively large. AR is affected by the covalency of the Er3+ ion sites and corresponds to the Ω6 value.

Structural and conductivity studies of fast ion conducting silver based tellurate glasses

Varying formers compositions of fast ionic conducting silveraresenotellurate (SAT) quaternary glasses were prepared by melt quenching technique. X-ray diffraction (XRD) measurements were carried out and confirmed the glassy nature of all SAT samples from the observed peak free XRD spectra. Fourier transform infrared (FTIR) spectra were recorded for all SAT sample pellets and confirmed the formation of structural coordination in all compositions of SAT compounds. Differential scanning calorimetric (DSC) measurements were made and estimated glass transition temperature ( T g) for all SAT samples. Impedance measurements were made on all SAT samples from 40 Hz to 100 KHz. Impedance data were analyzed using Boukamp equivalent circuit software and evaluated conductivity of each composition of SAT system. The observed variation of conductivity with former composition is explained by correlating XRD, FTIR, DSC and conductivity results with available theoretical models.

Potassium doping of semiconducting vanadium tellurate glasses

Glasses of the ternary system 2TeO 2 xK 2O(1− x)V 2O 5 have been prepared for x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol%. For each composition only one glass transition T g is observed in the temperature range 497–517 K. For each composition, the conductivity data were obtained in the temperature range 323–473 K, using impedance techniques. They obey an Arrhenius relationship with a composition independent pre-exponential factor. The isothermal conductivity curves exhibit a sharp minimum near x=0.5. The experimental data suggest that a polaron hopping mechanism operates in the electronically conducting domain of 0≤ x<5 and an interstitial pair mechanism operates in the ionically conducting domain of 0.5< x≤1. The very low conductivity expected for x=0.5 could be explained by assuming that, for this composition, both ionic and electronic paths would not percolate any more.

Mixed former effect in sodium phospho tellurate glasses

Glasses in the binary system xNa 2 P 2 O 6-( l − x) Na 2 Te 2 O 5 have been synthesised for 0≤ x ≤1. For all compositions, the glasses are transparent and appear homogeneous. Nevertheless for compositions near x = 0.4 glasses seem to be heterogeneous on SEM observations. Glass transition temperatures for all the compositions are between 220 and 310 °C. Conductivity data have been obtained using impedance techniques in the 100–250 °C temperature range. The σT product obeys an Arrhenius relationship with a composition-independent pre-exponential term A. The value of log A ≈ 4.8 is in agreement with an indirect interstitial mechanism model for sodium cation migration. Isothermal conductivity curves with x show a maximum in the ionic conductivity. This mixed network former effect may be justified by assuming an endothermic mixture between sodium phosphate and sodium tellurate.

Variation of glass transition temperature, Tg, with average coordination number, 〉 m〈, in network glasses: evidence of a threshold behavior in the slope |d Tg/ d〉 m〈 | at the rigidity percolation threshold (〉 m〈 = 2.4)

Alkali oxide (Ak 2O) addition to telluria lowers glass transition temperature, T g, of (Ak 2O) x (TeO 2) 1− x glasses systematically, with the slope d T g/d x displaying a local maximum at x c ≅ 0.18 corresponding to 〉 m〈 ≅ 2.4, the rigidity percolation threshold. In covalent network glasses, as in the present alkali tellurate glasses, T g is found to increase with 〉 m〈 with the slope |d T g/d〉 m〈| displaying a maximum near 〉 m〈≅2.4. It is recognized that this threshold behavior can be traced to a qualitative increase of molecular relaxation time near 〉 m〈≅2.4, where a condition for mechanical equilibrium is locally satisfied. This increase leads to a local T g(〉 m〈) enhancement at 〉 m〈 = 2.4 due to a kinetic effect, which is superposed on a quasi-linear T g(〉 m〈) variation with 〉 m〈 due to chemical effects.