V2O5 TeO2 Glasses Research Articles

Enhancing electrical properties through in-situ controlled nanocrystallization of V2O5–TeO2 glass

V2O5–TeO2 glass–ceramics (VTGC) were prepared by controlled annealing of the V2O5–TeO2 glass (VTG), which illustrates a parent glass matrix with a single charge carrier. The annealing proceeded at six temperatures selected between the glass transition and the maximum of the first crystallization process to obtain various nanocrystallite sizes. Heat treatment caused an increase in DC conductivity by 2.5–3.5 (250–285 °C) order of magnitude. Using thermal analysis, the crystal growth process was determined to be 1D. Structural studies show that the obtained materials are partially amorphous and polycrystalline with nanometer-sized crystallites. Subtle thread-like structures were observed using conductive AFM. The activation energy of the conduction process decreased from 0.38 eV in VTG to 0.18–0.11 eV (250–285 °C) in VTGC. The radii of crystallites were calculated based on the theoretical model of electron hopping between connected semiconducting nanocrystallites and vary between 1.7 and 2.8 nm (250–285 °C). Thermoelectric studies indicate constant carrier concentration. Features characteristic of small polaron hopping-governed materials were observed. We suggest V3O7 nanocrystals as conductive media in VTGC.Graphical abstract

Physical and Thermoelectric Properties of Ternary Semiconducting NiO–V2O5–TeO2 Glasses

Five samples of ternary semiconducting 65V2O5 –xNiO–(35–x) TeO2 glasses, with 5 ≤ x ≤ 25 (x in mol%), were prepared using a press-quenching method from a glass melt. The thermoelectric Power (TEP), density, oxygen molar volume (Vm) and x-ray diffraction (XRD) were analyzed. TEP measurements were conducted within the temperature range of 300 – 506 K for the mentioned glass compositions. Information on the creation of polarons and the disorder energy arising from random fields was gathered. By applying Heikes’ equation and the small polaron model theory to the TEP, the results obtained from experimental data were effectively explained. The study revealed that an increase in the NiO content in the glass led to a rise in density and a consistent decrease in molar volume. All glasses exhibited a singular phase structure.

Investigation of the glass forming regularity and thermal behavior of lead-free V2O5-TeO2-RO (R = Ca, Sr, Ba) low temperature sealing glass for electronics packaging

Lead-free V2O5-TeO2 glass systems are promising new sealant materials for electronics vacuum packaging, with low-melting temperature and unique light absorption. The glass forming regularity, structure and corresponding properties of the V2O5-TeO2-RO (R=Ca, Sr, Ba) glass system are systematically studied and analyzed in this paper. The results show that there is a wide glass forming region for the V2O5-TeO2-RO glass system, and with the increase of TeO2/V2O5 molar ratio, the thermal stability of V2O5-TeO2-SrO glass with the RO content of 20 mol% increases and the coefficient of thermal expansion increase from 11.2 to 15.86 × 10–6/°C due to transformation process of glass network structure from the [VO4] to transition state [TeO3 + 1] and [TeO3] group. The higher initial crystallization temperature of 40 mol%V2O5-40 mol%TeO2-20 mol%SrO glass is conducive to the flow of the glass slurry during the sealing process, obtaining a sealing device with good airtightness at extremely low temperatures of 350 °C.

Increasing the conductivity of V2O5-TeO2 glass by crystallization: structure and charge transfer studies

In the present paper, V2O5-TeO2 glass was prepared by the melt-quenching technique. Crystallization of glass with a vanadium content higher than 35%mol results in an increase in electrical conductivity by a few orders of magnitude and a decrease in activation energy from ~0.40 to ~0.12 eV. In this work, a critical review of existing charge transfer models was presented on the example of V2O5-TeO2 glass and glass–ceramics. Schnakenberg’s and Friedman-Triberis’ charge transfer models were found to be applicable to both glass and glass–ceramics. Optical phonon frequencies obtained from Schnakenberg’s model are in agreement with FTIR studies. Values of activation energies obtained from the Schnakenberg model decrease after crystallization. Friedman-Triberis’ model shows an increase in the density of states near the Fermi level from 1019 eV−1 cm−3 in glass, to 1021 eV−1 cm−3 in glass ceramics. Structural studies show that the main crystallizing phase is Te2V2O9 which occurs with the V2O5 shell in glasses with compositions 50–50%mol and 45–55%mol. It is concluded that crystallization results in the reduction of vanadium ions in the remaining glass matrix which leads to an increase in the V4+/V5+ ratio and therefore, an increase in electrical conductivity.

V2O5-P2O5-TeO2 glass anodes for Li-ion batteries

Understanding the role of network formers in affecting the electrochemical performances of the glass anodes for Li-ion batteries (LIBs) is of great importance for developing novel glass anode materials. In this work, we substitute the network former P2O5 for partial amount of TeO2 in V2O5-TeO2 glass composition and probe the effect of this substitution on both the microstructure and performances of the LIB anodes. The network structure of the glass before and after discharging/charging cycles is revealed at atomistic level by advanced Solid-State Nuclear Magnetic Resonance spectroscopy and X-ray photoelectron spectroscopy. The results show that, upon the insertion/extraction of Li+ ions, the structural network of the glass anode is irreversibly disassociated into many polyhedral species that congregate to form different kinds of nanoclusters. The substitution of P2O5 for TeO2 promotes the formation of Li2Te and the reduction of V5+ to V4+, and thereby enhances the capacity of the glass anodes.

Polarizability, Optical Basicity, and Photon Attenuation Properties of Ag2O–MoO3–V2O5–TeO2 Glasses: The Role of Silver Oxide

Polarizability, Optical Basicity, and Photon Attenuation Properties of Ag2O–MoO3–V2O5–TeO2 Glasses: The Role of Silver Oxide

Glass anodes for lithium ion batteries: Insight from the structural evolution during discharging/charging

AbstractGlasses are promising anode materials for Li‐ion batteries (LIBs) owing to their unique open network structures and the absence of grain boundaries. Upon discharging/charging, both the capacity and cycle life of the glass anodes can be affected through their structural evolutions. This review article highlights the recent research advances in improving and understanding the electrochemical performances of various types of glass anodes. Both the SnO‐ and GeO2‐based glass anodes suffer from the high initial capacity loss and short cycle life. The origin of the first‐cycle irreversible capacity loss is discussed primarily from the structural evolution with cycles, that is, forming metallic Sn/Ge in the glass matrix. Recently, significant breakthroughs have been achieved in enhancing cycling stability and capacity of the anode materials by means of the disorder‐order engineering with respect to the V2O5–TeO2 glass systems. In addition, the most recent advances in the applications of dual‐phase glass anodes in LiBs are reviewed. This article gives an overview of the applications of the glass anodes, as well as deals with the structural factors affecting their electrochemical performances. A deeper understanding of these factors will enable further steps toward improvement and application of the glass anodes for LIBs.

Tellurium nanoparticles enhanced electrochemical performances of TeO2-V2O5-Al2O3 glass anode for Lithium-ion batteries

Recently we developed a superior V2O5-TeO2 (VT) glass anode for Lithium-ion batteries (LIBs) by the disorder/order engineering. In this work, we investigate the effect of Al2O3 doping on the physical, thermal and electrochemical properties of the V2O5-TeO2 glass anode. To do so, we prepared the glass samples with the composition of xAl2O3-(100-x) (TeO2-V2O5) (x = 3, 5, 8, and 10 mol%) (AVT). The results show that there exists a critical Al2O3 content, i.e., 5 mol% Al2O3, which gave LiBs the highest capacity of 202 mA h g−1 after 1000 cycles of discharging/charging under the current density of 1 A g−1 and the lowest charge-transfer resistance before cycling. The disorder-order transition was found to take place in the AVT glass anodes, accompanied by formation of tellurium nanocrystals after 1000 cycles at 1 A g−1. Both the Te nanocrystals and the glass matrix synergistically enhanced the capacity and the cycling stability of the AVT glass anode. These findings are useful for designing and developing new types of glass anodes with high capacity and long cycling life for LiBs.

The study of glass transition temperature in Sb–V2O5–TeO2 glasses at different heating rates

The glass transition of xSb–(60 − x)V2O5–40TeO2 glasses with 0 < x <15 (in mol%) at different heating rates (φ = 3–12 K/min) has been studied using differential scanning calorimetry. The glass transition temperature (Tg) and crystallization temperature (Tcr) of these glasses have been determined. The effects of the heating rate and the Sb content on Tg have been discussed. It has been observed that the transition region shifts to higher temperatures when the measuring time is reduced. The compositional dependence of Tg has been determined and so an empirical equation has been deduced relating the glass transition temperature with the Sb concentration. Also, the value of glass-forming tendency has been studied for the present glasses.

Crystallization kinetic of Sb–V2O5–TeO2 glasses investigated by DSC and their elastic moduli and Poisson’s ratio

Ternary tellurate glasses of the form xSb–(60−x)V2O5–40TeO2 (0≤x≤15 in mol%) were prepared by using the usual melt quenching method. Differential scanning calorimetry (DSC) at different heating rates (φ) was used to thermal analyze and to gain more insight in to the thermal stability, glass forming tendency and so calorimetric behavior of the present glasses. The glass transition temperature (Tg), the temperature corresponding to the onset of crystallization (Tx) and also the crystallization temperature (TCr) were obtained at different heating rates, to estimate the key kinetic parameter of activation energy of crystallization (ΔE) by using different empirical formulas. Also some other thermal parameters such as thermal stability and glass forming tendency were determined. It was found that Tg, Tx and TCr increase with increase in Sb content and also with increase in heating rate. Moreover, Makishima–Makenzie’s theory was employed to evaluate the Poisson’s ratio and elastic moduli, indicating a strong relation between elastic properties and the structure of glass. From the mechanical and thermal data and also the values of oxygen molar volume (VO⁎), it was founded that the glass systems can be divided in to “two compositional regions”; so, results indicate that glasses with 10≤x≤15 (especially for x=12) are more thermal stable and strong glasses, which make them as more useful and promising materials in technological advantages and device manufacturing.

Effect of V2O5–TeO2 Glass Addition on Dielectric Properties of CaCu3Ti4O12 Ceramics Prepared by Solid State Method

CaCu3Ti4O12 (CCTO) is well known to have colossal dielectric constant in the range of 105. However, CCTO has considerably high dielectric loss values (tanδ > 0.1) at room temperature and 1 kHz. In this work, addition of glass to CCTO was suggested in order to improve its dielectric properties. The effect of V2O5–TeO2 (VT) glass addition on microstructure and dielectric properties of CCTO ceramics were investigated. Dielectric measurements were carried out for (1 − x) CCTO-(x) V2O5–TeO2 (x = 0, 0.03, 0.05, 0.10) samples in the frequency range of 102–106 Hz using impedance spectrometer. Electron micrographs showed that low melting VT glass addition facilitated the grain growth of CCTO. As VT glass amount increased, dielectric constant decreased. The drop, though within reasonable values (~105), may related to the presence of grain boundary glassy phase which itself has low dielectric constant. However, the dielectric loss of the composite has decreased after VT glass addition. The low melting V2O5–TeO2 glass aided in liquid phase sintering and improved the grain boundary resistance which resulted in decreased leakage currents.

Transport and dielectric properties of V2O5-MnO-TeO2 glasses

The frequency (1-10 kHz) and temperature (80-350 K) dependences of the ac conductivity and dielectric constant of the V2O5-MnO-TeO2 system, containing two transition-metal ions, have been measured. The dc conductivity dc measured in the high-temperature range (200-450 K) decreases with addition of the oxide MnO. This is considered to be due to the formation of bonds such as V--O--Mn and Mn--O--Mn in the glass. The conductivity arises mainly from polaron hopping between V4+M and V5+ ions. It is found that a mechanism of adiabatic small-polaron hopping is the most appropriate conduction model for these glasses. This is in sharp contrast with the behaviour of the Mn-free V2O5-TeO2 glass, in which non-adiabatic hopping takes place. High-temperature conductivity data satisfy Mott's small-polaron hopping model and also a model proposed by Schnakenberg in 1968. A power-law behaviour ( ac = Aωs , with s < 1) is well exhibited by the ac conductivity σac data of these glasses. Analysis of dielectric data indicates a Debye-type relaxation behaviour with a distribution of relaxation times. The MnO-concentration-dependent σac data follow an overlapping large-polaron tunnelling model over the entire range of temperatures studied. The estimated model parameters are reasonable and consistent with changes in composition.

Structure of vanadium tellurite glasses studied by neutron and X-ray diffraction

Details of the Te–O first-neighbor distances in V2O5–TeO2 glasses were obtained by neutron diffraction experiments with a measuring range up to Qmax=400nm−1 (Q is the magnitude of scattering vector). A sharp Te–O peak at 0.191nm and a second broad component at about 0.21nm were resolved. Quantitative analyses of the areas of both peak components for a compositional series of four samples support the model of a change of TeO4 trigonal bipyramids to TeO3 trigonal pyramids upon V2O5 additions. In glasses of up to ∼10mol% V2O5 each VOn polyhedron introduced is accompanied by the formation of a TeO3 unit. The number of TeO3 units increases further for glasses of higher V2O5 concentrations but the increase is less than that of the number of V sites.

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

The structures of V2O5-TeO2 glasses are investigated by means of 125Te and 51V 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 V2O5 content. The structures of V2O5-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 V2O5 content. Both chains consisting of tellurite structural units and those consisting of vanadate structural units contribute to the formation of the glass network in V2O5-TeO2 glasses.

Relaxation studies on V2O5-TeO2 glasses using heterogeneous conductor model

The dielectric modulus spectra of glasses in the system V2O5-TeO2 have been studied as a function of frequency in the temperature range 230 to 330K. A heterogeneous conductor model developed recently with the assumption of a sinusoidally varying local conductivity in the conducting phase has been successfully applied to analyse the data in this glass system. The Kohlrausch-Williams-Watts (KWW) stretched exponential function has also been used to fit the measured modulus spectra. The exponentβ is found to be correlated to the conductivity fluctuation in the conducting phase as assumed in the heterogeneous model.

Electrical Conduction and Structure of Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;-TeO&lt;sub&gt;2&lt;/sub&gt; Glasses (Part 2)

The structure of V2O5-TeO2 glasses containing Fe2O3 was investigated. Addition of Fe2O3 extended the glass formation region up to 80mol% V2O5. The Mossbauer spectra indicated that Fe ions were 3-valent and tetrahedrally coordinated. An IR absorption peak or the shoulder attributed to V=O was observed. The O1s photoelectron spectra were measured using MgKα emission and analyzed. Two O1s spectra were separated, and the difference in the binding energies of these two peaks was about the same as that between O1s spectra of bridging oxygen, BO, and of non-bridging oxygen, NBO, or of double-bonded oxygen, DBO. The high energy peak corresponded to BO and the low energy peak to NBO and DBO. These results suggest that these glasses have a layerlike vanadate network structure.

Electrical Conduction and Structure of Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-V&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;-TeO&lt;sub&gt;2&lt;/sub&gt; Glasses (Part 1)

V2O5-TeO2 glasses containing more than 80mol% V2O5 were obtained by moderate quenching of melts with addition of Fe2O3. These glasses are semiconductive by the small polaron hopping mechanism. The hopping process has been concluded to be adiabatic for [V2O5]≥50mol%. Fe ions, as well as V ions, seem to contribute to the hopping conduction, as suggested for Fe2O3-V2O5-P2O5 glasses. Dc conductivity of the tellurite glasses was more than 1 order of magnitude higher than that of phosphate glasses for [V2O5]≥70mol%. However, conductivities of both glasses were in the same order for [V2O5]≅80mol%. Relatively low conductivity of the tellurite glasses containing about 80mol% V2O5 was attributed to the very low value of the fraction of reduced V ion.

Spectroscopic, electrical and EPR studies of binary semiconducting oxide glasses containing 50 mol% V2O5

Recent measurements on the V2O5-GeO2 glass system consisting of an equimolar mixture of V2O5 and GeO2 revealed that increase in electrical conductivity of these glasses upon annealing could be attributed to the increase in V4+ and V3+ content which accompanied the microstructure formation. In the present work we report a similar study on V2O5-TeO2 and V2O5-P2O5 glass systems. It was found that in tellurite glass V3+ content increased upon annealing and V4+ content remained unchanged. In phosphate glass some increase in V4+ and no significant change in V3+ contents were observed. V3+ and V4+ contents in glasses could be best estimated from optical and electron paramagnetic resonance spectra, respectively.

Dielectric relaxation and modulus of V2O5—TeO2glasses

Abstract The dielectric behaviour of V2O5—TeO2 glasses in the composition range 10 to 80 mol.% V2O5 is reported for the temperature region 77 to 500 K and the frequency region 0.1 to 100 kHz. The variation of dielectric constant έ’ with temperature and frequency in the region where the measured a.c. conductivity approaches the d.c. conductivity indicates a bulk dielectric relaxation. The data have been analysed in terms of conventional dipolar dielectric relaxation with a distribution of dielectric relaxation times and in terms of conductivity relaxation using dielectric modulus M* = 1/e* plots. The d.c. conductivity, dielectric relaxation and conductivity relaxation have the same activation energy of 0.21–0.42 eV for decreasing V2O5 content and a frequency factor v 0 of 5 × 1010 Hz. The difference between this value and the 1012 Hz expected for phonon frequencies is attributed to a tunnelling contribution. The dielectric modulus approach is satisfactory for electronic glasses with respect to the calculat...

AC conductivity of V2O5-TeO2glasses

The electrical conductivity and dielectric constant of V2O5-TeO2 glasses of compositions 10-80 mol% V2O5 have been measured in the frequency range 0.1-100 kHz and in the temperature range 77-400K. A frequency dependence according to the relation sigma ( omega )=A omega s has been observed, and values of the exponent s are less than unity (between 0.95 and 0.80 depending on the composition). The data of AC conductivity have been analysed in the light of different theoretical models based on quantum-mechanical tunnelling (QMT) and hopping over the barrier (HOB). The analysis shows that neither QMT nor HOB models can explain the data quantitatively. A linear dependence of the conductivity and a temperature-independent s at low temperatures, and a non-linear increase of conductivity at higher temperatures for higher frequencies agree respectively with QMT and HOB models. It is difficult to estimate the absolute value of tau 0 (characteristic relaxation time of the system) or to arrive at a definite conclusion about the conduction mechanism by the Butcher and Morys model (1973) owing to experimental uncertainties in the measured values epsilon '( omega ) and the lack of knowledge of epsilon infinity . A detailed investigation of epsilon ' as a function of composition for these glasses has been made. A non-linear variation of dielectric constant with concentration has been observed. The abnormally high dielectric constant ( approximately 30) of the low composition V2O5-TeO2 glasses may be attributed to the characteristic role played by the glass former, TeO2.