Thermally stimulated discharge current (TSDC) and dielectric constant of semiconducting glasses

In this paper the results of thermally stimulated discharge current (TSDC) and dielectric constant for 40PbO-60Bi₂O₃ glass thermoelectrets are presented. Measurements of TSDC and dielectric constant, ǵe, have been carried out in the temperature range 30–300°C. The thermoelectrets were prepared at different polarizing fields. The various observed peaks in the thermograms are discussed on the basis of space charge polarization. The trap energy is evaluated from the Garlick-Gibson plot of initial rise method. Similarly other parameters such as relaxation time, charge release etc are evaluated.     

Electrical and dielectric analysis of phosphate based glasses doped with alkali oxides

In this work, new phosphate glasses with the molar composition 20.7P₂O₅–17.2Nb₂O₅–13.8WO₃–34.5A₂O–13.8B₂O₃ where A = Li, Na and K were prepared using the melt quenching technique. These types of glasses have potential to absorb hydrogen in its structure, which makes them promising materials to be used as electrolytes in intermediate temperature fuel cells. Additionally, niobium phosphate glasses can also have applications such as glass fibers, optical lenses, hermetic sealing and electrodes. The structure of the obtained samples was analyzed using Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), and Raman spectroscopy and the morphology by Scanning Electron Microscopy (SEM). The DTA measurements revealed values of glass transition temperature around 415 °C, and the Raman analysis showed that the amount of alkali and niobium oxides included on the studied compositions, successfully disrupted the P–O–P chains characteristic of the phosphate glasses. Dc (σ_dc) and ac (σ_ac) conductivities and dielectric spectroscopy measurements were performed as function of the temperature (200–370 K) which presented conductivity predominantly ionic (σ_electronic/σ_ionic of about 10^− 4). The dielectric spectroscopy was measured in the frequency range 100–1 MHz.     

Vibrational spectra of some binary semiconducting oxide glasses

The frequency-dependent complex relative permittivities of binary semiconducting V₂O₅-P₂O₅ glasses containing various amounts of vanadium have been measured at ambient temperature in the infrared region by power reflection spectroscopy. The measured values of the static constant, ₀, and high frequency constant, _x, are used to calculate the small polaron binding energy,W _p and the activation energy for conduction in the vanadium phosphate glasses, and comparisons are made with published data.     

Nonequilibrium and hysteretic low temperature dielectric response to strain in glasses

We present data on the nonequilibrium ac dielectric response of amorphous insulators to the application of a quasi-dc mechanical strain field below 150 mK. The behavior of the system after perturbation by a strain field is analogous to that observed after the application of a dc electrical field. In the current theoretical framework the nonequilibrium response is due to a time dependent density of states correction resulting from TLS-TLS interactions. In addition, an anomalous hysteresis in fast strain and electric field sweeps is reported which may represent the predicted dynamical response of relaxing independent TLS.     

Properties and structure of semiconducting sodium iron germanoborate glasses

Several properties of semiconducting Na₂B₄O₇–GeO₂–Fe₂O₃ glasses have been measured. These properties include Mössbauer, density, d.c. conductivity, thermal expansion coefficient, glass transition temperature (T _g), and softening temperature (T _s). The d.c. conductivity was found to decrease as the iron content increases while the activation energy increases with increasing iron content in the glasses. From the conductivity temperature relation, it was found that the small polaron hopping model was applicable at temperature above _D/2 (_D: the Debye temperature); and the electrical conduction at T>_D/2 was due to non-adiabatic small polaron hopping of electrons between iron ions. The parameters obtained from the fits of the experimental data to this model appear reasonable and are consistent with the glass composition. Dilatometric measurements indicated that the thermal expansion coefficient decreases with the increase of iron content whereas both of the (T _g) and the (T _s) increase with increasing iron content. Different behaviors were observed in the Fourier transform infrared (FTIR) absorption spectra as a result of the progressive replacement of GeO₂ by Fe₂O₃. In the case of 20 and 25 mol % GeO₂, simultaneous existence of [GeO₄] and [GeO₆] polyhedra can be observed in the glass network. Below 20 mol % GeO₂, all germanium participating into the glass network is tetrahedrally coordinated, that is [GeO₄]. It is also indicated that, with the increase of iron content, boron attains an enhanced state for its coordination number to increase from 3 to 4, and consequently the tetrahedral [BO₄] units increase at the expense of the trigonal [BO₃] units, indicating the increase of the bridging character. The results of the measured properties were correlated with those from the FTIR spectroscopy.     

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.     

Non-adiabatic polaron hopping conduction in semiconducting V2O5-Bi2O3 oxide glasses doped with BaTiO3

BaTiO₃-doped (5–40 wt %) 90V₂O₅-10Bi₂O₃ (VB) glasses have been prepared by a quick quenching technique. The d.c. electrical conductivities, _d.c., of these glasses have been reported in the temperature range 80–450 K. The electrical conductivity of these glasses, which arises due to the presence of V⁴⁺ and V⁵⁺ ions, has been analysed in the light of the small-polaron hopping conduction mechanism. The adiabatic hopping conduction valid for the undoped VB glasses (with 80–95 mol % V₂O₅), in the high-temperature region, is changed to a non-adiabatic hopping mechanism in the BaTiO₃-doped VB glasses. At lower temperatures, however, a variable range hopping (VRH) mechanism dominates the conduction mechanism in both the glass systems. Such a change-over from adiabatic to non-adiabatic conduction mechanism is a new feature in transition metal oxide glasses. Various parameters, such as density of states at the Fermi level N(E_F), electron wave-function decay constant, , polaron radius, r _p, and its effective mass, m _p ^* , etc., have been obtained for all the glass samples from a critical analysis of the electrical conductivity data satisfying the theory of polaron hopping conduction.     

Structural study of semiconducting and superionic conducting silver vanadate glasses

A structural study of semiconducting and superionic conducting silver vanadate glasses, containing 40 mol% Agl and 1 mol %⁵⁷Fe₂O₃, is performed by means of Mössbauer spectroscopy. Distinct composition dependency of Mössbauer parameters ( and ) of Fe³⁺ ions, having a minimum when Ag₂O content is 30 mol %, suggests that increasing Ag₂O content results in a gradual change of the glass matrix from a two-dimensional layer structure composed of VO₅ tetragonal pyramids to a chain structure composed of VO₄ tetrahedra. An increase in the Mössbauer parameters observed when the Ag₂O content is higher than 30 mol %, corresponding to a metavanadate structure (Ag₂O/V₂O₅=1), indicates a reverse change of the glass matrix into a complicated two- or three-dimensional network structure composed of VO₄ tetrahedra. These conclusions are in good agreement with those obtained from a distinct composition dependency of glass transition temperatures (T _g). Composition dependency of electrical conductivity at room temperature suggests that the structural change of glass matrix primarily affects the semiconductivity caused by a step-by-step electron hopping from V⁴⁺ to V⁵⁺ ions.     

Optical properties of samarium doped zinc-tellurite glasses

Glasses with the composition, (Sm₂ O ₃) _x (ZnO)_(40-x)(TeO ₂)₍₆₀₎, were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been explained.     

掺稀土离子玻璃的光放大效应

光放大材料是光纤放大器的主要组成部分，它决定光纤放大器的光放大功率。本文介绍了掺稀土离子如Er^3 、Nd^3 、Pr^3 及Dy^3 等玻璃的光放大原理以及影响光放大的各种因素。稀土离子本身存在的多种发射跃迁、无辐射跃迁，稀土离子间相互作用以及玻璃基质都影响稀土离子的光放大跃迁效率。上述分析对掺稀土离子玻璃的光放大材料性能的改进和新材料的设计可提供有益的指导。     

Ag doped chalcogenide glasses and their applications

Ag-doped chalcogenide glasses and amorphous thin films, their preparation, properties, photodoping, photoinduced surface deposition and applications, are reviewed, expanding on the results obtained recently. The progress obtained is not only connected with better understanding of their structure, chemical bonding and properties but also in application of Ag-containing glasses and films in solid-state batteries, electrochemical sensors and optoelectronics (gratings, microlenses, waveguides, optical memories, non-linear effects).     

Synthesis and characterization of cadmium doped lead-borate glasses

Cadmium doped lead-borate glasses were prepared from the melts in appropriate proportions of PbO₂, H₃BO₃ and (15–40 mol%) CdO mixture in the temperature range 700–950°C. The infrared spectra of the glasses in the range 400–4000 cm^-1 show their structures. No boroxol ring formation was observed in the structure of these glasses. Furthermore, doped cadmium atoms were not seen in tetrahedral coordination. But the conversion of three-fold to four-fold coordination of boron atoms in the structure of glasses was observed.     

Infrared spectra of zinc doped lead borate glasses

The infrared spectra of zinc-doped lead borate glasses (10–30 mol% ZnO) were measured over a continuous spectral range (400–4000 cm⁻¹) in an attempt to study their structure systematically. No boroxol ring formation was observed in the structure of these glasses. The formation of Zn in tetrahedral coordination was not observed. The conversion of three-fold to four-fold coordinated boron took place.     

The effects of semiconducting screens on the dielectric loss of liquid nitrogen impregnated taped cable insulation

The effect of semiconducting screens on the dielectric loss of liquid nitrogen impregnated taped insulation has been studied. Three mechanisms for the screen loss are considered, that is, (a) — particles from the screen oscillating in the butt gaps or in the interstices of a cellulose structured materials, (b) — a screen electrical resistivity effect, not as yet fully understood but which explains much of the phenomena observed for different tape materials; (c) — loss due to partial discharges, this has been shown to be predominant near dielectric breakdown.Mechanism (a) which is favoured for conventional (ambient) paper/oil dielectrics does not appear to be a major factor in the present situation.Most of the tests are in conjunction with six layers of Tyvek tape insulation, increase in the number of tape layers of different dielectric materials with carbon-black screens produce a general trend for the overall loss (carbon-black screen plus dielectric itself) to decrease towards the loss for the unscreened dielectric.     

Surface nucleated crystallization in Ge15Te80As5 semiconducting glasses

The crystalline morphology of electrically conductive surface layers in thermally annealed bulk samples of Ge₁₅Te₈₀As₅ glass has been studied using a scanning electron microscope. Results confirm previous suggestions that crystallization is surface nucleated. Two regions of different crystalline morphology are observed and result from a two-stage crystallization process. Selected-area electron diffraction on extracted particles was used to identify the crystalline phases. The crystallites near the inner glassy material are Te, the first phase to segregate upon annealing. The crystalline material near the sample surface is more dense and contains two phases: GeTe (second-stage crystallization product) and crystalline Te. Energy Dispersive X-Ray Analysis with spacial resolution of 2–3 μm and accuracy of ±10% has shown that the “average” composition is the same for these crystalline regions and for the glassy material.     

Absorption and emission properties of Ho doped lead-zinc-borate glasses

This paper reports on the affect of lead content on the absorption and emission spectra of the Ho³⁺ ion doped lead-zinc-borate glasses in the composition (mol%) of (20 − x)PbO-20ZnO-(59 + x)B₂O₃-1.0Ho₂O₃ where x = 0, 5,10,15 of PbO content with λ_exc = 405 nm. The experimental absorption band energies have satisfactorily been correlated with the theoretical results with an r.m.s deviation of zero with the following correction factors obtained by a least square fit analysis: ΔE¹ = 348.495936 cm^− 1, ΔE² = 1.436043 cm^− 1, ΔE³ =  46.481575 cm^− 1, Δξ_4f = − 28.512979 cm^− 1, Δα = 55.508936 cm^− 1, Δβ = − 1394.339908 cm^− 1 and Δγ = 1208.424336 cm^− 1. By applying the Judd-Ofelt intensity parameter Ω₂ has been found to be linearly decreasing with the PbO content from 5 to 10 mol% and then increasing. And also radiative (A, A_T, β, τ_r) characteristic factors of the luminescent transitions (⁵I₈ ← ⁵F_3,4,5 and ⁵S₂) of the glasses have been evaluated. Stimulated emission cross-sections (σ_p^E) of the measured emission transitions of holmium glasses have also been computed.     

Thermal and optical properties of tellurite glasses doped erbium

Er³⁺-doped tellurite glasses with molar compositions of 75TeO₂–20ZnO–(5 − x) Na₂O–xEr₂O₃ (x = 0, 0.5, 1, 2, 3, and 4 mol%) have been elaborated from the melt-quenching method. The effects of Er₂O₃ concentration on the thermal stability and optical properties of tellurite glasses have been discussed. From the differential scanning calorimetry (DSC) profile, the glass transition temperature T _g, and crystallization onset temperature T _x are estimated. The thermal stability factor, defined as ∆T = T _x − T _g, was higher than 100 °C. It suggests that tellurite glass exhibits a good thermal stability and consequently is suitable to be a potential candidate for fiber drawing. Furthermore, the stability factor increases with Er₂O₃ concentration up to 2 mol% then presents a continue decrease suggesting of beginning of crystallization of highly doped tellurite glasses. The refractive index and extinction coefficient data were obtained by analyzing the experimental spectra of tanΨ and cos∆ measured by spectroscopic ellipsometry (SE). The complex dielectric functions (ε = ε₁ + iε₂) of the samples were estimated from regression analysis. The fundamental absorption edge has been identified from the optical absorption spectra and was analyzed in terms of the theory proposed by Davis and Mott. The values of optical band gap for direct and indirect allowed transitions have been determined. An important decrease of the optical band gap was found after Er doping. It was assigned to structural changes induced from the formation of non-bridging oxygen. The absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach’s tail. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions.