Electrical properties and infrared spectra of TeO2-Fe2O3 glasses

The d.c. and a.c. electrical properties on TeO₂-Fe₂O₃ glasses with various compositions of PbO, B₂O₃ and SiO₂ were studied over a frequency range of 10²–10⁵ Hz and in the temperature range 300–500 K. The a.c. conductivity is proportional tow ⁿ, and the conduction mechanism is due to an electronic hopping process. The effects of composition and temperature on the dielectric constant and loss factor (tan ) were studied. The infrared absorption spectra of these glasses reveal that the addition of PbO, B₂O₃ and SiO₂ of these glasses does not introduce any new absorption band in the infrared spectrum of TeO₂-Fe₂O₃ glasses. These results prove the distribution of TeO₄ polyhedra which determines the network and basic oscillation of the building units in the tellurite glasses.     

Manifestation of Nd ions on the structure,Raman and IR spectra of (TeO<Subscript>2</Subscript>-MoO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>) glasses

The structure of [80TeO₂ + (20–x)MoO + xNd₂O₃] glasses, with x = 0, 4, 6, 10 and 12 mol%, is studied in this work. Raman scattering in the spectral range (−2000 to 3500 cm⁻¹) and IR absorption spectra have been measured for crystalline TeO₂ and glasses, and their assignments were discussed and compared. Many vibrational modes were found active in both Raman and IR and their assignments for crystalline TeO₂ and for the glasses were discussed in relation to the tetragonal structure of crystalline α -TeO₂. Nd₂O₃ was found to completely eliminate diffuse scattering and enhance the Raman scattering intensity. Anti-stokes Raman bands in the range −1460 cm^{− 1} to −1975 cm^{− 1} were observed for both (30Li₂O + 70B₂O₃+ xNd₂O₃) glasses and [80TeO₂ + (20−x)MoO + xNd₂O₃] glasses and were attributed to some emission processes due to the doping of the glasses with Nd₂O₃.     

Non-linear concentration-dependent electrical properties of some semiconducting vanadate glasses

Characterizations of (50 – x) P₂O₅-x M-50V₂O₅ (M = Bi₂O₃, Sb₂O₃, and GeO₂ and x=0 to 45 mol% M) and P₂O₅-Bi₂O₃ semiconducting oxide glasses have been made from studies of electrical conductivities (both a.c. and d.c.) in the temperature range 77 to 400 K. All these glasses showed some interesting non-linear variation of d.c. and a.c. conductivity, together with other properties for particular values of M (between 20 and 30 mol% M). Because the non-vanadate (1–x) P₂O₅-x Bi₂O₃ glasses also showed similar conductivity anomaly (minimum) around 25 mol% Bi₂O₃ with a corresponding maximum in the activation energy (W), it is concluded (in contradiction to earlier suggestions) that not only the ratio (= V⁵⁺/V⁴⁺) but also the network-former ions in the vanadate glasses make a substantial contribution to the anomalous concentration variation of the physical properties of these glasses. The electrical conduction in these glasses is found to be mainly due to hopping of polarons in the adiabatic approximation. At low temperature, the d.c. conductivity obeys Mott's T ^–1/4 behaviour. The a.c. conductivity obeying the general ^s law (exponent s lying between 0.85 and 0.98) supports the theory based on the hopping over the barrier model.     

Electron spin resonance in copper phosphate and copper tellurite glasses containing strontium

Two series of ternary copper phosphate and copper tellurite glasses containing strontium were prepared and the electron spin resonance spectra of glasses of compositions 65 (P₂O₅)-(35-x) CuO-xSrO and 65 (TeO₂)-(35-x) CuO-xSrO where x varied from 0–10 mol % were investigated. From the results and the chemical analyses of the samples it was found that a reduction in the copper (II) signal intensity in the glass samples as the proportion of alkaline earth metal is raised, corresponds to an increase in the reduced valency ratio, C, in the glasses.     

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.     

Ac conductivity of BaTiO3 containing (90V2O5-10P2O5) oxide glasses dispersed with nanocrystalline particles

The frequency dependent AC conductivity (_ac) of some new multicomponent (1 – x) (90V₂O₅-10P₂O₅) + xBaTiO₃ (x = 0.1 to 0.9) type glasses containing nanocrystalline BaTiO₃ particles (observed from the transmission electron microscopic study) has been reported in the temperature range 80–400 K. The behavior of _ac is broadly similar to what has been observed previously in many other amorphous semiconductors and polymers (namely nearly linear frequency dependence and weak temperature dependence). Analysis of the experimental conductivity data shows that Long's overlapping large polaron tunneling (OLPT) mechanism is the most probable mechanism of conduction for the present BaTiO₃ doped glasses. The Quantum mechanical tunneling (QMT) model and the classical hopping of electrons over a barrier can, however, explain the AC conductivity data only below _D/2–160 K (_D is the Debye temperature). Reasonable values of the relaxation time and barrier heights related to the models have been obtained from the fits of the conductivity data.     

Crystallization and properties of CaO-P2O2-B2O3 glasses

Glasses were prepared with compositions (50–0.5 x) CaO.(50–0.5 x) P₂O₅ · x B₂O₃ with B₂O₃ contents (x) from 0 to 45 mol%. The glass transformation temperature (T _g), dilatational softening temperature (T _D) and Vickers hardness (H _V) initially increased with x, but showed maxima at about x=20 for T _g and T _D and at about x=35 for H _V. The thermal expansion coefficient decreased with x, levelling off at about 35 mol% B₂O₃. The maximum tendency to crystallize occurred at around 25 mol% B₂O₃. Volume nucleation (and hence glass-ceramic formation) and surface nucleation were obtained for x between 15 and 25 mol%. The first phase to appear was BPO₄, which was probably homogeneously nucleated. Subsequently the 4CaO · P₂O₅ phase was heterogeneously nucleated on the BPO₄. For 10 x 35 only surface nucleation was observed. The kinetics of nucleation were investigated in the 20 mol% B₂O₃ glass. The changes in properties and crystallisation behaviour with B₂O₃ content were related to short-range structural information. Infrared spectra and literature data indicated a threedimensional network of B-O-B and B-O-P linkages in the glasses.     

Thermal conductivity of the vitreous system (ZnO) x −(P2O5)1−x

Glasses of the system (ZnO)_x–(P₂O₅)_1–x have been prepared by melting ZnO with anhydrous P₂O₅ in open crucibles. These glasses had compositions ranging from 20 to 70 mol % ZnO (chemically analysed ZnO mol %). Measurements of the thermal conductivity for the present glass system have been made in the temperature range 305 to 630 K. The thermal conductivity of this glass system is mainly due to lattice thermal vibrations. The thermal conductivity data are found to be fairly sensitive to the ZnO mol % content. It is observed from these data that the present glass system can be divided into three compositional regions. This behaviour is qualitatively explained in terms of changes in glass structure.     

A study of electron spin resonance of copper phosphate glasses containing tellurium oxide

Electron paramagnetic resonance in glasses of compositions (P₂O₅)_100–x-(CuO)_x and (P₂O₅)₅₀-(TeO₂)_50–x-(CuO)_x where x varied from 20 to 40 mol% has been investigated. The distribution of the copper between the two main valency states is determined from measurements of e.s.r. arising from the Cu²⁺ centres. The study of e.s.r. enables the distribution of copper in the glasses between the different valency states to be determined and thus indirectly provides evidence for hopping conduction in the glasses. From the results of e.s.r. and the chemical analysis of the samples it is found that the reduced valency ratioC, i.e. the ratio of the concentration of Cu⁺ ions to that of total copper in the glass, increases with increasing CuO content.     

Small polaron transport in V2O5–NiO–TeO2 glasses

Semiconducting glasses of the V₂O₅–NiO–TeO₂ system were prepared by the press-quenching method and their d.c. conductivities in the temperature range 300–450 K were measured. The d.c. conductivities at 395 K for the present glasses were determined to be 10^–7 to 10^–1 S m^–1, indicating that the conductivity increased with increasing V₂O₅ concentration. A glass of composition 67.5V₂O₅–2.5NiO–30TeO₂ (mol %) having a conductivity of 2.47×10^–2 S m^–1 at a temperature of 395 K was found to be the most conductive glass among the vanadium-tellurite glasses. From the conductivity–temperature relation, it was found that a small polaron hopping model was applicable at the temperature above _D/2 (_D: the Debye temperature); the electrical conduction at T>_D/2 was due to adiabatic small polaron hopping of electrons between vanadium ions. The polaron bandwidth ranged from 0.06 to 0.21 eV. The hopping carrier mobility varied from 1.1×10^–7 to 5.48×10^–5 cm² V^–1 s^–1 at 400 K. The carrier density is evaluated to be 1.85×10¹⁹–5.50×10¹⁹ cm^–3. The conductivity of the present glasses was primarily determined by hopping carrier mobility. In the low-temperature (below _D/2) regime, however, both Mott's variable-range hopping and Greaves intermediate range hopping models are found to be applicable.     

Effects of Al2O3 addition on the sinterability and ionic conductivity of nasicon

The effects Al₂O₃ doping on the sintering behaviour and ionic conductivity of nasicon have been investigated using formulations of Na_3+2x Zr₂Si₂Al _x P_1–x O₁₂ where Al³⁺ ions were substituted to P⁵⁺ sites within the range 0x0.2. The density of Na_3+2x Zr₂Si₂Al _x P_1–x O₁₂ was increased with increasing amount of Al₂O₃ doping due to the enhanced liquid-phase sintering. The relative density of Na_3.4Zr₂Si₂Al_0.2P_0.8O₁₂ reached a maximum value of 96% when sintered at 1200°C for more than 7 h. The maximum conductivity of 0.24 ^–1 cm^–1 at 300°C was obtained for the composition with x=0.1 when sintered at 1200°C for 10 h.     

Direct current electrical conduction in lead tungsten phosphate glasses

Measurements have been made on d.c. electrical conductivity of semiconducting lead tungsten phosphate glasses (X mol% WO₃–(60–x) mol% PbO–40 mol% P₂O₅;x= 10, 20, 30, 40, 50 and 60) of six different compositions over a temperature range of 240 to 500 K. It is shown that the conduction can be described by a small polaron hopping model. When the WO₃ content is 30 mol% the d.c. conductivity _dc decreases and the activation energyW increases with increasing WO₃ content and the glass samples exhibit predominant ionic conduction, however, when the WO₃ content is > 30 mol%, _dc increases andW decreases with the increase of tungsten ion concentration and the glass samples exhibit electronic conduction. The electronic conduction in these glasses havingx > 30 mol% seems to be adiabatic. Greaves variable range hopping has been found to be valid. The value of the electron wavefunction decay constant a is of the order of 16 nm^–1. A minimum in the d.c. conductivity has been observed when the PbO concentration is 30 mol%.     

Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation

Electrical conductivities, , of the Li₂O-La₂O₃-SiO₂ glasses were investigated as functions of Ta₂O₅ doping and Ta ion-implantation. A linear relationship between logarithm and the inverse of the sample temperature, T, was found in 2 to 4 mol% Ta₂O5 doped Li₂O-La₂O₃-SiO₂ glasses. The conductivity increases as Ta₂O₅ content increases at sample temperatures above 100°C. Fluences of 50 keV Ta ions per cm² from 5 × 10¹⁶ to 2 × 10¹⁷ were implanted into 0% and 2% Ta₂O₅ containing Li₂O-La₂O₃-SiO₂ glass samples. The activation energy of the conductivity was deduced from the relation between log and 1/T. It was found in implanted samples that the conductivity increased, but the activation energy and T _k–100 decreased, where T _k–100 is the sample temperature when the conductivity reaches 100 × 10^–1 S/cm. However, the Ta₂O₅ containing implanted samples show higher conductivities, lower activation energies and lower T _k–100. X-ray photoelectron spectroscopy (XPS) was used to study the structural modification introduced by implantation. Bridging oxygen (BO) and non-bridging oxygen (NBO), were observed in all samples. The changes in relative concentrations of BO and NBO before and after implantation clearly indicate the structure modification which results in the increase of the conductivity. It was clearly demonstrated in this study that both doping Ta₂O₅ and implanting Ta ions enhance the conductivity of Li₂O-La₂O₃-SiO₂ electrode glasses.     

Glass formation region and lithium ion conduction in the oxyfluorophosphate glasses

Oxyfluorophosphate glasses containing about 80 mol% of [LiF+Li₂O] show unusually high lithium ion conductivity at elevated temperatures. A detailed investigation has been carried out on the glasses prepared by both conventional cooling and a rapid quenching technique. Chemical analysis of the glasses reveals fluorine loss during melting and it becomes difficult to make glasses with exact predetermined compositions. Electrical conductivity of the glasses, determined from complex impedance analysis increases with Li₂O content. A glass with nominal composition 70 LiF15 Li₂O15 Al(PO₃)₃ shows the highest conductivity (~ 1.3×10^–3 ohm^–1 cm^–1 around 200° C) among all the compositions studied. An interesting feature of the impedance plot is the near perfect semicircle for bulk relaxation indicating a narrow distribution of relaxation times. This has been explained on the basis of a relatively small proportion of lithium ions which are mobile. The electrical conductivity of the glasses is found to be essentailly independent of dissolved water content. The infrared spectra of these glasses (2 to 50m region) could not produce much useful structural information.     

Incorporation of LiNbO3 crystals into tellurite glasses

Transparent tellurite glasses containing 5–10 m diameter LiNbO₃ crystals (3–7 wt%) have been successfully prepared using an incorporation method in which LiNbO₃ crystals are directly dispersed into the 80TeO₂-15Li₂O-5Nb₂O₅ glass. The dissolution behaviour of the LiNbO₃ crystals greatly depends on the Li₂O: Nb₂O₅ ratio in the matrix glasses. In the 80TeO₂-10Li₂O-10Nb₂O₅ matrix glass, the crystals remaining after incorporation have the composition LiNb₃O₈. A small difference in the refractive indices, n, between the TeO₂-based glasses (n=2.07) and the incorporated LiNbO₃ crystals (n=2.296) is a significant reason for the transparency. It is feasible to prepare the highly transparent TeO₂-based glasses containing a large amount of LiNbO₃ crystals by controlling the incorporation process.     

Effect of heat treatment and irradiation on electrical conductivity and crystallization in the BaO-B2O3-Fe2O3 glass system

A glass system was prepared according to the formula 75 mol % B₂O₃-(25 –x) mol % BaO –x mol % Fe₂O₃, wherex = 0, 1, 2.5, 5, 7.5 and 10. The glasses were subjected to heat treatment at 550° C for 2, 6, 12, 18 and 24 h. The glasses were also irradiated using-rays at a dose of 4.805 × 10⁴ rad h^–1 for 12, 18 and 24 h. An X-ray diffraction technique was used to identify the separated crystalline phases. The electrical conductivity and activation energy of untreated, heat-treated and irradiated samples were measured and calculated. The rate and the dimensions of crystallization were also calculated by using the Avrami equation. It was found that-Fe₂O₃ is the separated phase when a sample containing 7.5 mol% Fe₂O₃ is heat treated for 24h;-Fe₂O₃ and Fe₂O₃ are the separated phases when the sample containing 10 mol% Fe₂O₃ is heat treated for 6, 12 and 18 h, with the addition of BaO when the sample is heat treated for 24 h. A miminum value for the electrical conductivity of glass samples was found to occur around an Fe₂O₃/BaO ratio of 0.425. The rate of crystallization in the sample containing 10 mol% Fe₂O₃ is 1.30607 × 10^–3 and the geometry of crystallizationn is 1.2238, which indicates that the crystallization was in one dimension.     

Doping of calcium titanate with chromium and indium

The lattice parameters and composition range of orthorhombic CaTi_{1 – x} Cr_xO_{3 –} solid solutions were determined by x-ray powder diffraction. Samples with the nominal compositions CaTi_{1 – y} In_yO_{3 –} , synthesized in the range y=0.05–0.3, consisted of two phases: CaTiO_{3 –} and a CaIn₂O₄-based phase. The compositions of the synthesized phases were checked by x-ray microanalysis. The electrical conductivity of the CaTi_{1 – x} Cr_xO_{3 –} (0 < × 0.2)solid solutions was measured as a function of oxygen partial pressure (0.21 × 10⁴ to 1.0 × 10^–11 Pa) at 900 and 1000°C. Cr doping of calcium titanate was shown to increase its conductivity. A mechanism of defect formation in doped calcium titanate was inferred from conductivity versus data.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 475–478.Original Russian Text Copyright © 2005 by Murashkina, Demina.     

Electron paramagnetic resonance of Cu2+ and VO2+ ions in phosphate glasses

Electron spin resonance (ESR) spectra ofx(CuO · V₂O₅ (1 –x) (Na₂O · P₂O₅) andx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) glasses for 0 x 40 have been studied at the X-band and at 300 K. It is found that forx 5, both Cu²⁺ and VO²⁺ are present, mostly as isolated species. Forx 10, broad resonance lines atg = 2.1524 forx(CuO · V₂O₅) (1 –x) (Na₂O · P₂O₅) and atg = 2.1448 forx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) are observed which may be mainly due to dipole-dipole type interaction between transition metal (TM) ions. Spin Hamiltonian parameters of TM ions have been calculated. Optical spectra of the sodium phosphate glasses doped with single TM ions have also been studied. The theoretical optical basicity, A_th, of these doped glasses has been calculated. It is found that for VO²⁺ ionsg ,g and increase whileA ,P and g _|/g decrease with increase in A_th. However, no significant change is observed in the spin Hamiltonian parameters of Cu²⁺ with the change in A_th.     

Dielectric, magnetic and spectroscopic properties of Li2O–WO3–P2O5 glass system with Ag2O as additive

Li₂O–WO₃–P₂O₅ glasses containing small concentrations of Ag₂O from 0 to 1 mol% were prepared. A number of studies viz., chemical durability, dielectric studies (constant ′, loss tan δ, a.c. conductivity σ_ac over a range of frequency and temperature), spectroscopic (infrared, optical absorption ESR spectra) and magnetic susceptibility studies of these glasses, have been carried out. The interesting variations observed in all these properties with the concentration of Ag⁺ ions have been analyzed in the light of different oxidation states and environment of tungsten ions in the glass network.     

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part II Electrical transport behavior

Electrical transport behaviour of the valence compensated system Ca_1–x La _x Ti_1–x Cr _x O ₃ (x 0.50) has been investigated by studying the Seebeck co-efficient, DC and AC conductivity as a function of temperature. Seebeck co-efficient, DC conductivity of different compositions has been measured in the temperature range 300 K–1000 K. AC conductivity for different compositions were determined in the temperature range 100–550 K and frequency range 10 Hz–10 MHz. Positive values of Seebeck co-efficient show that holes are the majority charge carriers. Conduction seems to occur by correlated barrier hopping of holes among Cr³⁺and Cr⁴⁺ions or V_O and V_O . Almost equal values of activation energies obtained for DC conductivity and dielectric relaxation process show that both the processes occur by the same mechanism.