The glass transition temperature and infrared absorption spectra of: (70−x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Glasses of the system: (70−x) TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (T_g) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO₂ by Li₂O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm⁻¹. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.     

Studies of some mechanical and optical properties of: (70 − x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Specimens of the glassy system: (70 − x)TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by the melt-quenching. An ultrasonic pulse-echo technique was employed, at 5 MHz, for measuring: the ultrasonic attenuation, longitudinal and shear wave velocities, elastic moduli, Poisson ratio, Debye temperature and hardness of the present glasses. It is found that the gradual replacement of TeO₂ by Li₂O in the glass matrix up to 30 mol% leads to decrease the average crosslink density and rigidity of prepared samples which affects the properties, i.e., the hardness, ultrasonic wave velocities and elastic moduli are decreased, while the Poisson ratio and the ultrasonic attenuation are increased. Also, optical absorption spectra were recorded in the range, 200-800 nm for these glasses. The obtained results showed that a gradual shift in the fundamental absorption edge toward longer wavelengths occurred. Values of both of the optical energy gap, E_opt, and width tails, ΔE, are determined. It is observed that E_opt is decreased and ΔE increased with the increase of Li₂O in the glass matrix up to 30 mol%. The compositional dependences of the above properties are discussed and correlated to the structure of tested glasses.     

The comparative structure, properties, and ionic conductivity of LiI + Li2S + GeS2 glasses doped with Ga2S3 and La2S3

The well known and characterized fast ion conducting (FIC) LiI + Li₂S + GeS₂ glass-forming system has been further optimized for higher ionic conductivity and improved thermal and chemical stability required for next generation solid electrolyte applications by doping with Ga₂S₃ and La₂S₃. These trivalent dopants are expected to eliminate terminal and non-bridging sulfur (NBS) anions thereby increasing the network connectivity while at the same time increasing the Li⁺ ion conductivity by creating lower basicity [(Ga or La)S_4/2]⁻ anion sites. Consistent with the finding that the glass-forming range for the Ga₂S₃ doped compositions is larger than that for the La₂S₃ compositions, the addition of Ga₂S₃ is found to eliminate NBS units to create bridging sulfur (BS) units that not only gives an improvement to the thermal stability, but also maintains and in some cases increases the ionic conductivity. The compositions with the highest Ga₂S₃ content showed the highest T_gs of ∼325 °C. The addition of La₂S₃ to the base glasses, by comparison, is found to create NBS by forming high coordination octahedral LaS₆³⁻ sites, but yet still improved the chemical stability of the glass in dry air and retained its high ionic conductivity and thermal stability. Significantly, at comparable concentrations of Li₂S and Ga₂S₃ or La₂S₃, the La₂S₃-doped glasses showed the higher conductivities. The addition of the LiI to the glass compositions not only improved the glass-forming ability of the compositions, but also increased the ionic conductivity glasses. LiI concentrations from 0 to 40 mol% improved the conductivities of the Ga₂S₃ glasses from ∼10⁻⁵ to ∼10⁻³ (Ω cm)⁻¹ and of the La₂S₃ glasses from ∼10⁻⁴ to ∼10⁻³ (Ω cm)⁻¹ at room temperature. A maximum conductivity of ∼10⁻³ (Ω cm)⁻¹ at room temperature was observed for all of the glasses and this value is comparable to some of the best Li ion conductors in a sulfide glass system. Yet these new compositions are markedly more thermally and chemically stable than most Li⁺ ion conducting sulfide glasses. LiI additions decreased the T_gs and T_cs of the glasses, but increased the stability towards crystallization (T_c − T_g).     

Spectroscopic properties of Er-doped xGeO2-(80 − x)TeO2-10ZnO-10BaO glasses

Erbium-doped glasses with composition xGeO₂-(80 − x)TeO₂-10ZnO-10BaO were prepared by melt-quenching technique. The phonon sideband spectra and the optical absorption band edges for the host matrix were confirmed by means of the spectral measurements. Standard Judd-Ofelt calculations have been completed to these glasses. The dependence of up-conversion and infrared emission under 980 nm excitation on the glass composition was studied. The quantum efficiencies for the ⁴I_13/2 → ⁴I_15/2 transition of trivalent erbium in the glasses were estimated.     

Preparation and characterization of glasses in the Ag2S + B2S3 + GeS2 system

The glass forming range of the Ag₂S + B₂S₃ + GeS₂ ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag-B-Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS_4/2 and AgBS_4/2, and trigonal units, BS_3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS_3/2 and Ag₃B₃S₃S_3/2 six membered rings, are also observed in these glasses at higher Ag₂S modification levels because the further addition of Ag₂S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag₂S goes into the GeS₂ subnetwork to form Ag₃S₃GeS_1/2 groups before going to the B₂S₃ subnetwork. In doing so, it is suggested that B₁₀S₂₀ supertetrahedra exist in Ag₂S + B₂S₃ and Ag₂S + B₂S₃ + GeS₂ glasses. Significantly B-S-Ge bonds form in the B₂S₃ + GeS₂ glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.     

The structure and optical properties of GeO2-GeS2 glasses

Oxy-chalcogenide glasses with compositions of xGeO₂-(100 − x)GeS₂, where 0 ? x ? 100 mol%, have been prepared and studied in terms of their structures and optical properties. X-ray fluorescence spectroscopy shows that Ge:S ratio can deviate from GeS₂ by ∼10 at.%, depending critically upon the preparation conditions. Raman scattering spectroscopy suggests that stoichiometric GeO₂-GeS₂ glasses have a heterogeneous structure in the scale of 1-100 nm. The optical gaps are nearly constant at 3.0-3.5 eV for glasses with 0 ? x ? 80 mol% and abruptly increase to ∼6 eV in GeO₂. This dependence suggests that the optical gap is governed by GeS₂ clusters, which are isolated and/or percolated. Composition-deviated glasses appear as orange and brown, and these glasses seem to have more inhomogeneous structures.     

Structure and properties of glasses in the MI + M2S + (0.1Ga2S3 + 0.9GeS2), M = Li, Na, K and Cs, system

The structure and properties of glasses in the MI + M₂S + (0.1Ga₂S₃ + 0.9GeS₂), M = Li, Na, K and Cs, system were studied using Raman, IR spectroscopy, DSC and density measurements to help better understand the ionic transport in these glasses. The glass forming ranges of these ternary glasses were compared to those of the binary alkali sulfide and germanium sulfide systems. The more extensive glass forming range in the Na₂S system was used to examine the more extensive changes of structure and properties of these glasses as a function of Na₂S content. As expected, non-bridging sulfurs (NBS) form with the addition of alkali sulfide. Unlike their oxide counterparts, however, the alkali sulfide doped glasses appear to support longer-range super-structural units. For example, evidence that the adamantine-like structure exists in the K₂S and Cs₂S modified glasses is found in the Raman spectra of the glasses. The structural role of the alkali iodide addition was also explored since the addition of alkali iodide helps to improve the conductivity. For most of these glasses, as observed in many other oxide glasses, the added MI dissolves interstitially into the glass structure network without changing the alkali sulfide network structure. In 0.6Na₂S + 0.4(0.1Ga₂S₃ + 0.9GeS₂) glasses, however, the added NaI may affect the glass structure as it causes systematic changes in the frequency of the Ge-S network mode as seen in the Raman spectra.     

Structure and properties of lithium thio-boro-germanate glasses

Structural studies of the ternary xLi₂S + (1 − x)[0.5B₂S₃ + 0.5GeS₂] glasses using IR, Raman, and ¹¹B NMR show that the Li₂S is not shared proportionately between the GeS₂ and B₂S₃ sub-networks of the glass. The IR spectra indicate that the B₂S₃ glass network is under-doped in comparison to the corresponding composition in the xLi₂S + (1 − x)B₂S₃ binary system. Additionally, the Raman spectra show that the GeS₂ glass network is over-modified. Surprisingly, however, the ¹¹Boron static NMR gives evidence that ∼80% of the boron atoms are in tetrahedral coordinated. A super macro tetrahedron, B₁₀S₁₈⁻⁶ is proposed as one of the structures in these glasses in which can account for the apparent low fraction of Li₂S present in the B₂S₃ sub-network while at the same time enabling the high fraction of tetrahedral borons in the glass.     

Insulator-like electrical transport in structurally ordered Al65Cu20+xRu15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5) icosahedral quasicrystals

Low-temperature resistivities, in zero-field and 8 T field, and magnetoresistance have been measured down to 1.4-300 K for stable icosahedral quasicrystals Al₆₅Cu_20+xRu_15−x (x = 1.5, 1.0, 0.5, 0.0 and −0.5). The analysis of the magnetoresistance data shows an overwhelming presence of anti weak-localization effect (τ_so ∼ 10⁻¹² s). But the sample with x = −0.5 shows anomalous magnetoresistance and the anti weak-localization effect breaks down (τ_so to be 10⁻¹⁵ s). The in-field σ-T between 5 K and 20 K, for x = 1.0, 0.5, 0.0 and −0.5 samples, and between 1.4 K and 40 K for x = 1.5 sample, follow a power-law behavior with an exponent of 0.5 and above ∼30 K the exponent ranges from 1.17 to 1.58. The observed power-laws basically characterize the presence of critical regime of the metal-insulator (MI) transition, dominated by electron-electron and electron-phonon inelastic scattering events respectively. In samples with x = 1.0, 0.5, 0.0 and −0.5 the in field σ-T has been found to follow ln σ-vs-T^1/4 below 5 K, which indicates the presence of variable range hopping. The observed transport features indicate the occurrence of proximity of metal-insulator transition in these Al-Cu-Ru quasicrystal samples.     

Transport property and structural characterization studies on (1 − x)[0.75AgI:0.25AgCl]:xTiO2 conducting composite electrolyte system

Transport property and structural investigation have been carried out on newly synthesized Ag⁺ ion conducting composite electrolyte system. The composite electrolyte system (1 − x)[0.75AgI:0.25AgCl]:xTiO₂, where 0 ? x ? 0.5 (in molar weight fraction) has been synthesized by melt quenching and annealing methods. The chemical compound TiO₂ (second phase dispersoid) dispersed in different compositions in a quenched (0.75AgI:0.25AgCl) mixed system/solid solution; this solid solution was used as a first phase host salt in place of AgI. The different preparation routes were adopted for the composite electrolyte system. Composition x = 0.1 exhibited highest conductivity at room temperature. The composite system 0.9[0.75AgI:0.25AgCl]:0.1TiO₂ was synthesized at different soaking times by melt quenching method. The system exhibited optimum conductivity at 20 min soaking time (σ_rt ≈ 1.4 × 10⁻³ S/cm). The ac conductivity has been measured from Z′-Z″ (Cole-Cole) complex impedance plots using impedance spectroscopic (IS) technique. The electrical conductivity as a function of temperature and frequency has been studied, and activation energy E_a, was calculated from Arrhenius plots for all compositions (0 ? x ? 0.5). The dc conductivity value has been evaluated from Log σ vs. log f plots. Structural characterization studies were carried out by X-ray diffraction (XRD) and differential thermal analysis (DSC) techniques.     

Spectrometric and ellipsometric studies of (1 − x)TiO2 · xLn2O3 (Ln = Nd, Sm, Gd, Er, Yb) thin films

Spectrometric and ellipsometric studies of (1 − x)TiO₂ · xLn₂O₃ (Ln = Nd, Sm, Gd, Er, Yb; x = 0.33, 0.5) thin films at room temperature were performed. The obtained dispersion dependences of refractive indices are successfully described by the optical-refractometric relation. The dependence of optical pseudogap and refractive indices on composition and molar mass of the films is investigated. The influence of compositional disordering on the energy width of the exponential absorption edge is studied.     

Optical properties of Cr ion in lithium metasilicate Li2O · SiO2 transparent glass-ceramics

The optical properties of Cr³⁺ ions in lithium metasilicate (Li₂O · SiO₂) transparent glass-ceramics were investigated. The main crystalline phase precipitated was the lithium metasilicate (Li₂O · SiO₂) crystal. The percent crystallinity and crystalline size were ranging 65-75% and 20-35 nm, respectively. The color changes drastically to deep pink from emerald green upon crystallization. New and strong absorption bands appeared and the absorption intensity increases by about 10 times that in glass. These new absorption bands are found to be derived from Cr³⁺ ions in octahedral sites in the lithium metasilicate crystal lattice. Cr³⁺ ions substitute for three Li⁺ ions and occupy the distorted octahedral site between single [SiO₄]_n chains of lithium metasilicate crystal. The ligand field parameters can be estimated: 10Dq = 13 088 cm⁻¹, B = 453 cm⁻¹, Dq/B = 2.89 and C = 2036 cm⁻¹. The near-infrared luminescence centered at 1250 nm was not detected in the deep pink glass-ceramics unlike emerald green glass.     

Structure of partially reduced xPbO (1 − x)SiO2 glasses: combined EXAFS and MD study

We have studied the structure of partially reduced lead-silicate glasses using combined EXAFS (extended X-ray absorption fine structure) and MD (molecular dynamics) methods. The analysis was performed for glasses of x[(1 − p)Pb pPbO] (1 − x)SiO₂ composition, x = 0.3, 0.5, 0.7, where parameter (1 − p) describes the degree of reduction, i.e. the content of the granular metallic phase, appearing as the result of the reduction process (e.g. annealing in hydrogen atmosphere). In the EXAFS experiment (1 − p) was expressed via the time of reduction realized at 400 °C (1.5 h, 24 h, 70 h), whereas in the MD simulations it was determined precisely by using proper numbers of particles (corresponding to (1 − p) = 0.0, 0.25, 0.5, 0.75 and 1.0). In the paper we describe in detail the local structure around lead atoms and its changes in the function of glass composition and reduction degree. The tendency for agglomeration of Pb⁰ into clusters, the formation of the granular metallic phase, and continuity of silica and lead oxide subnetworks are discussed. A good agreement between EXAFS-extractcd and MD-extracted parameters of the short-range structure encouraged us to preform a medium-range order analysis, based on the MD simulations only. Moreover, combining the EXAFS and MD methods we could correlate the reduction time (technological parameter) with the degree of reduction (1 − p) and the actual state of the granular structure. The latter relation may be useful for controlled production of reduced glasses of pre-requcstcd physical properties.     

Spectroscopic and magnetic behavior of xNd2O3(1−x)(3Bi2O3 · PbO) glasses

Glasses of the xNd₂O₃(1−x)(3Bi₂O₃ · PbO) system with 0?x?0.30 were obtained and studied by IR spectroscopy, X-ray photoelectron spectroscopy (XPS), density and magnetic susceptibility measurements. IR and density measurements show that the addition of neodymium ions produces structural changes and the neodymium ions play a network modifier role in the host glass matrix. XPS investigation permitted following the evolution of the structural disorder, of the degree of polymerization of bismuthate chains and of the fraction of bridging oxygens with respect to the neodymium ion concentration of the studied glasses. Magnetic susceptibility data show that the Nd³⁺ ions are present as isolated species for x?0.05 and as both isolated and exchange coupled species for higher x values.     

Structure and electrical conductivity of new Li2O-CeO2-B2O3 glasses

Fourier transformation infrared spectra, density and DC electrical conductivity of 30Li₂O · xCeO₂⋅(70 − x)B₂O₃ glasses, where x ranged between 0 and 15 mol%, have been investigated. The results suggested that CeO₂ plays the role of network modifier up to 7.5 mol%. At higher concentrations it plays a dual role; where most of ceria plays the role of network former. The density was observed to increase with increasing CeO₂ content. The effect on density of the oxides in the glasses investigated is in the succession: B₂O₃ < Li₂O < CeO₂. Most of CeO₂ content was found to be associated with B₂O₃ network to convert BO₃ into B O₄⁻ units. The contribution of Li⁺ ions in the conduction process is much more than that due to small polarons. The conductivity of the glasses is mostly controlled by the Li⁺ ions concentration rather than the activation energy for CeO₂ > 5 mol%. Lower than 5 mol% CeO₂ the conductivity is controlled by both factors. The dependence of W on BO₄⁻ content supports the idea of ionic conduction in these glasses.     

Glass formation in and structural investigation of Li2S + GeS2 + GeO2 composition using Raman and IR spectroscopy

Li₂S + GeS₂ + GeO₂ ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO₂ concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S⁻) sulfurs are observed in Raman and IR spectra of binary Li₂S + GeS₂ glasses. Additions of GeO₂ to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S⁻) remain constant in intensity up to high GeO₂ concentrations. At higher concentrations of GeO₂ (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO₂ concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge⁴⁺ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li₂S + GeS₂ + GeO₂ glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.     

Vibrational, EPR and optical spectroscopy of the Cu doped glasses with (90-x)TeO2-10GeO2-xWO3 (7.5 ≤ x ≤ 30) composition

Infrared, EPR and optical absorption studies on (90-x)TeO₂-10GeO₂-xWO₃ (7.5 ≤ x ≤ 30) glasses containing Cu²⁺ spin probe have been carried out. The Infrared spectral studies show that the structure of glass network consists of [TeO₄], [TeO₃]/[TeO_3 + 1], [WO₄], [WO₆] and [GeO₆] units in the disordered manner. Physical parameters such as density (ρ), molar volume (V_m), oxygen packing density (OPD), oxygen molar volume (V_o), optical basicity (Λ), oxide ion polarizability (α_O²⁻), inter ionic distances and the concentration of ions per unit volume of Te, Ge, W, Cu and O have been determined. The spin-Hamiltonian parameters (g_||, g_⊥ and A_||) of Cu²⁺ ions in the present glasses have been estimated from EPR spectra at 300 K. Bonding parameters such as α², β₁², β², Γ_σ, and Γ_π have been calculated from both optical absorption and EPR data. The observed variations in spin-Hamiltonian parameters and bonding parameters have been correlated to the structural modifications due to the WO₃ incorporation into the TeO₂ glass network at constant 10 mol% GeO₂ content.     

Electrical transport properties of 0.5Li2O-0.5M2O-2B2O3 (M = Li, Na and K) glasses

Transparent glasses in the system 0.5Li₂O-0.5M₂O-2B₂O₃ (M = Li, Na and K) were fabricated via the conventional melt quenching technique. The amorphous and glassy nature of the samples was confirmed via the X-ray powder diffraction and the differential scanning calorimetry, respectively. The frequency and temperature dependent characteristics of the dielectric relaxation and the electrical conductivity were investigated in the 100 Hz-10 MHz frequency range. The imaginary part of the electric modulus spectra was modeled using an approximate solution of Kohrausch-Williams-Watts relation. The stretching exponent, β, was found to be temperature independent for 0.5Li₂O-0.5Na₂O-2B₂O₃ (LNBO) glasses. The activation energy associated with DC conduction was found to be higher (1.25 eV) for 0.5Li₂O-0.5K₂O-2B₂O₃ (LKBO) glasses than that of the other glass systems under study. This is attributed to the mixed cation effect.     

Thermodynamical miscibility in 0.8[xB2O3-(1 − x)P2O5]-0.2K2O glasses

The thermodynamical miscibility in 0.8[xB₂O₃-(1 − x)P₂O₅]-0.2K₂O glasses has been studied by measuring the glass transition temperature and the mixing enthalpy. Measurements have been performed by differential scanning calorimeter and hydrofluoric acid solution calorimetry at 298 K. The enthalpies of mixing are significantly negative over the whole range of composition. The results are discussed in terms of intermolecular associations.     

RDF analysis, positron annihilation and Raman spectroscopy of xTiO2-(60 − x)SiO2-40Na2O non-linear optical glasses: III. Non-bridging oxygen bonds tracing and structure analysis

xTiO₂-(60 − x)SiO₂-40Na₂O glasses have proven an interesting linear and non-linear optical properties [M. Abdel-Baki, F. Abdel Wahab, F. El-Diasty, Mater. Chem. Phys. 96 (2006) 201]. The investigated glasses show one order of magnitude enhancement for the second-order index of refraction and third-order optical susceptibility over some TiO₂ silicate glasses. In this work, we continue studying these glasses using three different techniques to analyze the glass structures seeking to provide a deep insight for the relation between structure, compositions and the optical characteristics of these glasses. Radial Distribution Function analysis (RDF) combined Raman spectroscopy are used to study these glasses. Positron annihilation lifetime spectroscopy and Doppler broadening measurements are carried out to investigate the change in the glass structure as the incorporation of TiO₂ concentration into glass. The origin of the non-bridging oxygen (NBO) bonds has been traced to correlate their existence with the measured non-linear optical properties of the investigated glasses.