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In this study, we investigate and compare the optical (linear/nonlinear) characteristics of lead borate and bismuth borate glasses. The refractive indices were measured using a Brewster’s angle setup, and the optical band gaps were determined experimentally by analyzing the optical absorption edge in Ref. 32. Molar refraction and electronic polarizability exhibit similar behavior. The metallization varies from 0.630 to 0.568 for lead borate glasses and from 0.526 to 0.435 for bismuth borate glasses as the PbO/Bi₂O₃ content increases. The transmission coefficients decreased from 0.884 to 0.846 for PbB glasses and from 0.818 to 0.751 for BiB glasses. The dielectric constant changed from 2.755 to 3.276 for PbB glasses and from 3.094 to 4.884 for BiB glasses. The optical electronegativity decreased from 0.964 to 0.792 for PbB and from 0.857 to 0.760 for BiB. The linear dielectric susceptibility increased from 0.139 to 0.181 for lead borate glasses and from 0.214 to 0.309 for bismuth borate glasses. The nonlinear optical susceptibility changed from $0.647\times 10^{-13}$ to $1.829\times 10^{-13}$esu for PbB and from $0.359\times 10^{-12}$ to $1.551\times 10^{-12}$esu for BiB, showing an increase of more than fivefold. The nonlinear refraction index varied from $1.470\times 10^{-12}$ to $3.810\times 10^{-12}$esu for lead borate glasses and from $0.704\times 10^{-11}$ to $2.646\times 10^{-11}$esu for bismuth borate glasses. The results indicate that bismuth borate is superior to lead borate for optical applications.

Structural changes induced by heat treatment of yttrium-aluminosilicate glasses doped with gadolinium were studied by thermal differential analysis, X-ray diffraction and Gd³⁺ electron paramagnetic resonance (EPR). A small amount of yttrium was replaced by gadolinium in the host glass because yttrium and gadolinium cations are quite similar, and gadolinium can be used as a structural sensor by electron paramagnetic resonance measurements. EPR results evidence small changes in the surroundings of Gd³⁺ ions in the heat treated samples, as compared with the as prepared ones.

Jamming of hard spheres is a new critical phenomenon whose exponents are different from those of the other known transitions. These exponents have been recently computed in a mean field approximation whose limits of validity are not known. Even if their values are in very good agreement with the ones obtained by accurate numerical simulations, the deep reasons for this success are not understood.

In this paper, after a brief presentation of the state of the art on the glass transition and jamming, I will discuss how this breakthrough can be the starting point of possible progresses in the following directions: the computation of the upper critical dimension for jamming, harmonic oscillations for soft spheres at low temperature, off-equilibrium behavior and quantum glassy effects.

Glasses and disordered materials are known to display anomalous features in the density of states, in the specific heat and in thermal transport. Nevertheless, in recent years, the question whether these properties are really anomalous (and peculiar of disordered systems) or rather more universal than previously thought, has emerged. New experimental and theoretical observations have questioned the origin of the boson peak (BP) and the linear in T specific heat exclusively from disorder and two-level systems (TLS). The same properties have been indeed observed in ordered or minimally disordered compounds and in incommensurate structures for which the standard explanations are not applicable. Using the formal analogy between phason modes (e.g., in quasicrystals and incommensurate lattices) and diffusions, and between amplitude modes and optical phonons, we suggest the existence of a more universal physics behind these properties. In particular, we strengthen the idea that linear in T specific heat is linked to low energy diffusive modes resulting from fundamental symmetries, and that a BP excess can be induced in crystals either by gapped optical-like modes and/or by anharmonic diffusive (Akhiezer) damping.

Mixed alkali borate xNa₂O-(30-x)K₂O-70 B₂O₃(5≤x≤25) glasses doped with 0.5 mol% of gadolinium ions have been investigated by using electron paramagnetic resonance (EPR) and optical absorption techniques, as a function of alkali content, to look for the "mixed alkali effect" on the spectral properties of the glasses. The EPR spectrum consists of three prominent features with effective g-values, g≈5.6, 2.8 and 2.0, and two weak features at g≈3.3 and 4.3. The three EPR signals at g≈2.0, g≈2.8 and g≈5.6 are attributed to Gd³⁺ ions located at sites with weak, intermediate and strong cubic symmetry fields, respectively. In principle these sites may be of network forming and network modifying types. Ionic radius considerations suggest that gadolinium ions cannot substitute the much smaller boron ions and thus only the network modifier site is acceptable. The number of spins (N) participating in resonance and its paramagnetic susceptibility (χ) for g≈5.6 resonance line have been calculated. It is interesting to note that N and χ increase with x and reach a maximum around x=15 and thereafter decrease showing the mixed alkali effect in these glasses. From ultraviolet absorption edges, the optical band gap energies were evaluated. It is interesting to note that the optical band gap energies for these glasses decrease slightly with increasing x and reach a minimum around x=10, and thereafter increase showing the mixed alkali effect. Optical band gap energies (E_opt) obtained in the present work vary from 2.20–3.35 eV for both the direct and indirect transitions. The physical parameters of the glasses have been evaluated with respect to the composition.

Glasses of the system x(CuO)(50-x)PbO:50V₂O₅ were prepared by melt quenching in the range x=0 mol% to 15 mol%. Measurements are reported for DC electrical conductivity for the above compositions in the temperature range 300–500 K. The experimental results are analyzed with reference to various theoretical models proposed for DC electrical conduction in amorphous semiconductors. The analysis shows that at high temperatures the temperature dependence of DC conductivity is consistent with Mott's model of phonon-assisted hopping conduction, variable range hopping mechanism and Schnakenberg's model mechanism. The high-temperature thermoelectric power was satisfactorily explained by Heikes' relation and the data also showed evidence of small polaron formation in these glasses.

Glasses of x(ZnO)(50 - x)PbO:50V₂O₅ system were prepared by melt-quench process in the range x = 0 mol% to 15 mol%. Measurements are reported for DC electrical conductivity as well as thermo electrical power for these samples in both glass and crystalline forms in the temperature range of 27°C and 227°C. The ESR studies of these samples at room temperature are reported. These spectra are characterized by well-resolved eight-line powder pattern. It is observed that the ESR spectra obtained in the crystalline form, the hyperfine structure is nearly smeared out and the spectra are characterized by a relatively broad line with an isotropic g value. The experimental results are analyzed with reference to Mott's model. The analysis shows that at high temperatures the temperature dependence of DC conductivity is consistent with Mott's model for both glass and crystalline samples. The high-temperature thermoelectric power was satisfactorily explained by Heikes' relation and the data also showed evidence of small polaron formation for glass form samples and large polaron formation in crystalline samples. These results indicate that all the glass samples lead metavanadate are n-type at room temperature and the crystalline samples are p-type at room temperature.

We use complete spatio-temporal characterization of an ultrashort pulse to study self-phase modulation and other propagation effects in a sample of SF59 optical glass. The goal of this work is to perform accurate experimental measurements of the optical parameters of material samples. From the measured dependence of the self-induced phase shift on the transverse coordinate, we deduce a value of the coefficient n₂ of the intensity-dependent refractive index that is in good agreement with previous measurements. We also observe that the spectrum of the transmitted pulse can be explained only approximately in terms of the solution to the nonlinear Schrödinger equation.

The precursor glasses in (mol%) 25.53Li₂O-21.53Ta₂O₅-35.29SiO₂-17.65Al₂O₃ (LTSA) and 25K₂O-25Nb₂O₅-50SiO₂ (KNS) glass systems were prepared by the melt-quench technique. Ferroelectric LiTaO₃ (LT) and KNbO₃ (KN) crystallites containing bulk nano glass-ceramics have been prepared by controlled crystallization of these precursor glasses respectively. Second harmonic generations (SHG) at 532 nm in both the glass-ceramics have been realized under fundamental beam of Nd³⁺:YAG laser source (1064 nm). The SHG power output has been found to increase up to 14 and 62.4 nJ with variation of rotation angle for LT and KN bulk nano glass-ceramics respectively due to orientation of ferroelectric domains under applied field.

With in glass forming region of Li₂O–WO₃–B₂O₃ glass system, a particular composition 40Li₂O–5WO₃–(55–x) B₂O₃: xV₂O₅ (with x ranging from 0.2 to 0.8, all are in mol.%) is chosen. The DSC traces are obtained to identify the glass transition temperature (T_g) and the glass forming ability of all the glass samples. The ESR and IR spectra portray the local structure of the glass system and valance states of the vanadium ions in the glass matrix. As the content of V₂O₅ increases up to 0.6 mol.% in the glass system, a gradual conversion of vanadium ions from V⁵⁺ state to V⁴⁺ state is observed, causing the depolymerization in the glass matrix by the transformation of several glass forming units BO₄ → BO₃ and WO₄ → WO₆.

The glass composition 40Li₂O–5WO₃–(55−x)B₂O₃: xV₂O₅ for x = 0.2, 0.4, 0.6 and 0.8 is chosen for the present study. The glass samples were synthesized by conventional melt-quenching technique. The dielectric properties such as constant (ε′), loss (tan δ) and ac conductivity (σ^ac) are carried out as a function of temperature (30–270°C) and frequency (10²–10⁵ Hz). The glass sample (at x = 0.6) exhibited highest ac conductivity (σ^ac) and spreading factor (β) among all the samples. All glasses exhibited mixed conduction (both electronic and ionic) at high temperatures. The frequency exponent s denotes the ac conduction mechanism is associated with both QMT model (at low temperatures) and CBH model (at high temperatures).

Modern levitation furnaces are enabling melting and freezing of refractory materials like Al₂O₃ to be studied in depth with synchrotron radiation techniques. Whilst α-Al₂O₃ is a close packed Debye-like solid, liquid Al₂O₃ has smaller coordination numbers and the structure has network-like characteristics. Under contactless conditions, substantial under cooling can be achieved. Melting involves a significant decrease in density which is approximately recovered on recrystallization, both of which can be followed with high speed video imaging. Freezing occurs with a burst of energy — recalescence — which substantially raises the temperature momentarily. Using Rietveld refinement the density of α-Al₂O₃ and the mean square displacement of the average atom 〈μ²〉 can be followed up to the melting point and upon freezing using in situ X-ray diffraction. As melting is approached 〈μ²〉 for α-Al₂O₃ exceeds the harmonic approximation of the Lindemann–Galvarry law and for liquid Al₂O₃ above the melting point 〈μ²〉 appears to be greater still. On freezing from the undercooled state α-Al₂O₃ is initially decompressed with the T - P point falling on the melting curve extrapolated to negative pressures.

So far only a handful of publications have been concerned with the study of the mixed alkali effect in borate glasses containing three types of alkali ions. In the present work, the mixed alkali effect (MAE) has been investigated in the glass system (40–x) K₂O–x Li₂O –10Na₂O–50B₂O₃.(0≤x≤40 mol%) through density and modulated DSC studies. The density and glass transition temperature of the present glasses varies non-linearly exhibiting mixed alkali effect. We report the mixed alkali effect in the present glasses through optical properties. From the absorption edge studies, the various values of optical band gap (E_o) and Urbach energy (ΔE) have been evaluated. The values of E_o and ΔE show non-linear behavior with compositional parameter showing the mixed alkali effect. The band gap energy based average electronic polarizability of oxide ions α_O2–(E_o), optical basicity A(E_o), and Yamashita–Kurosawa’s interaction parameter A(E_o) have been examined to check the correlations among them and bonding character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and interaction parameter, the present K₂O– Li₂O–Na₂O–B₂O₃ glasses are classified as normal ionic (basic) oxides.

Electron paramagnetic resonance (EPR) and optical absorption spectra of copper ions in xLiF-(50-x)Li₂O-20SrO-30Bi₂O₃ glass system have been studied. MDSC studies showed that the glass transition temperature decreases with LiF content. Optical absorption spectra of the pure glasses reveled that the cut off wave length increased and optical band gap energy decreased with increase in LiF content. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The Cu²⁺ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu²⁺ is d _{x2 y2} and the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d-d transition bands of Cu²⁺ ion. By correlating EPR and optical absorption data, the bond parameters are evaluated from various techniques.

Glasses having composition 20CdOxBi₂O₃(79.5-x)B₂O₃0.5Pr₆O₁₁ with x varying from 15 to 35 mol% have been synthesized. Optical absorption and fluorescence spectra were measured at ambient temperature. A close correlation is observed between the Bi₂O₃ content and the spectroscopic properties such as Judd-Ofelt intensity parameters Ω_λ = (λ = 2, 4, 6), radiative and structural properties of prepared glasses doped with Pr³⁺ ion. The variation of Ω₂ with Bi₂O₃ content has been attributed to changes in the asymmetry of the ligand field at the rare earth (RE) ion site (due to structural change) and to changes in RE-O covalency, whereas the variation of Ω₆ has been related to the variation in RE-O covalency. Following the luminescence spectra, various radiative properties like transition probability (A_rad), radiative lifetime (τ_r), branching ratio (β_r) and stimulated emission cross section (σ) have been calculated. The branching ratio for ³P₀ → ³F₂ transition of Pr³⁺ glass system arrive at 41 to 40%, respectively, and the predicted spontaneous radiative transition probability rates are high and varies from 14032 to 14864 s⁻¹. In addition, the glass stability is improved in which the substitution of B₂O₃ for Bi₂O₃ strengthens the glass network structure. The bismuth based glass as a host for Pr³⁺ ion doped suggesting their suitability for laser applications.

Ion conduction in noncrystals (glasses, polymers, etc) has a number of properties in common. In fact, from a purely phenomenological point of view, these properties are even more widely observed: ion conduction behaves much like electronic conduction in disordered materials (e.g., amorphous semiconductors). These universalities are subject of much current interest, for instance interpreted in the context of simple hopping models. In the present paper we first discuss the temperature dependence of the dc conductivity in hopping models and the importance of the percolation phenomenon. Next, the experimental (quasi)universality of the ac conductivity is discussed. It is shown that hopping models are able to reproduce the experimental finding that the response obeys time-temperature superposition, while at the same time a broad range of activation energies is involved in the conduction process. Again, percolation is the key to understanding what is going on. Finally, some open problems in the field are listed.

Thulium-doped potassium lanthanum gallate glasses (K₂O-La₂O₃-Ga₂O₃ or KLG) which are suitable to use in amplifiers has been fabricated and characterized. The density, the refractive indexes, the absorption and luminescence spectra were measured and analyzed. By using the Judd–Ofelt theory, the experimental oscillator strengths, the Judd–Ofelt intensity parameters Ω_t were determined, and some important radiative properties were calculated. Using a least-squares fitting approach, the Judd–Ofelt intensity parameters Ω_t were found to be Ω₂=7.26×10^-20cm², Ω₄=1.69×10^-20cm², and Ω₆=0.66×10^-20cm². The bandwidth of the ³H₄→³F₄ transition around 1.47μm in Tm³⁺-doped KLG glasses is ~92nm which is smaller than Tm³⁺-doped KBG glasses at ~120nm.