Network structure of molybdenum lead phosphate glasses: Infrared spectra and constants of elasticity

Molybdenum lead phosphate glasses doped with La₂O₃ of the system xMoO₃-5La₂O₃-50P₂O₅-(45−x)PbO, with 0≤x≤25 mol%, have been synthesized and studied by FTIR, ultrasonic and differential scanning calorimetry (DSC) in order to investigate the role of MoO₃ content on their atomic structure. The constants of elasticity and Debye temperatures of the glasses have been investigated using sound velocity measurements at 4 MHz. According to the IR analysis, the vibrations of the phosphate structural units are shifted towards higher wavenumbers associated with the formation of bridging oxygens. The change in density with MoO₃ content reveals that the molybdate units are less dense than the lead units. The observed compositional dependence of the constants of elasticity is interpreted in terms of the effect of MoO₃ on the different phosphate bonds. It is assumed that MoO₃ plays the role of a former by increasing the ultrasonic velocity and the constants of elasticity of the phosphate glasses.     

Influence of valence states and co-ordination of cobalt ions on dielectric properties of PbO-Bi2O3-As2O3:CoO glass system

The glasses of the composition (40−x) PbO-15Bi₂O₃-45As₂O₃-xCoO, with 0≤x≤0.6 mol% in the steps of 0.1 were synthesized. The dielectric properties viz., dielectric constant, loss and ac conductivity over moderately larger ranges of frequency and temperature were investigated. The results were analyzed with the aid of the data on optical absorption and IR spectra. The analysis indicated that there is an increase in the insulating strength of the glasses with increase in the concentration of CoO up to 0.4 mol%.     

Crystallization kinetics of Li2O-PbO-V2O5 glasses

Lead vanadate glasses of the system 5Li₂O−(45−x) PbO−(50+x) V₂O₅, with x=0, 5, 10, and 15 mol% have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC using continuous-heating techniques. In addition, from dependence of the glass-transition temperature (T_g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined and the crystallization mechanism was characterized. The results reveal the increase of the activation energy for glass transition which was attributed to the increase in the rigidity, the cross-link density and the packing density of these glasses. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of Li_0.30V₂O₅, Li_0.67O₅V₂, LiV₆O₁₅, Li₄O₄Pb, and O₇Pb₂V₂ in a remaining amorphous matrix.     

Structural investigation of xAg2O·(100−x)·[2B2O3·As2O3] glasses doped with manganese ions

Structural analysis of x[(100−y)Ag₂O·yMnO]·(100−x)[2B₂O₃·As₂O₃] glasses, with x=10 mol% and 0≤y≤10 mol%, was performed by means of FT-IR and FT-Raman spectroscopies. The purpose of this work is to investigate the structural changes that appear in the xAg₂O·(100−x)·[2B₂O₃·As₂O₃] glasses with the addition and increase in manganese ions content. FT-IR measurements revealed the presence of pyro-, ortho-, di-, tri-, tetra- and penta-borate groups and structural units characteristic to As₂O₃ in the structure of the studied glasses. FT-IR spectroscopy measurements also show that BO₃ units are the main structural units of the glass system. The presence of structural units characteristic to Ag₂O were not directly evidenced by FT-IR spectroscopy. In addtition, the FT-Raman analysis evidenced the presence of boroxol rings in the structure of the studied glasses.     

Spectroscopic study of ZnO doped CeO2-PbO-B2O3 glasses

Glass samples of compositions xZnO-xCeO₂-(30−x)PbO-(70−x)B₂O₃ with x varying from 2% to 10% mole fraction are prepared by the melt quench technique. The structural and optical analysis of glasses is carried out by XRD, FTIR, density and UV-visible spectroscopic measurement techniques. The FTIR spectral analysis indicates that with the addition of ZnO contents in glass network, structural units of BO₃ are transformed into BO₄. It has been observed in our previous work that band gap decreases from 2.89 to 2.30 eV for CeO₂-PbO-B₂O₃ glasses with cerium content varying from 0% to 10% [Gurinder Pal Singh, Davinder Paul Singh, Physica B 406(3) (2011) 640-644]. With the incorporation of zinc in CeO₂-PbO-B₂O₃ glasses, the optical band gap energy decreases further from 2.38 to 2.03 eV. This causes more compaction of the borate network, which results in an increase of density (3.39-4.02 g/cm³). Transmittance shows that ZnO in glass samples acts as a reducing agent thathelps to convert Ce⁴⁺→Ce³⁺ ions.     

FTIR structural investigation of gamma irradiated BaO–Na2O–B2O3–SiO2 glasses

Fourier transform infrared (FT-IR) spectra of xBaO–15Na₂O–(70−x)B₂O₃–15SiO₂ glass system with x=0, 5, 10, 15 and 20 (mol%) has been measured in the spectral range 400–4000 cm⁻¹ at room temperature in order to understand the characteristic frequencies of the chemical bonds and bonding mechanisms, which are susceptible to the structural and spectral changes. The effect of gamma irradiation in the dose range 0.1 kGy–60 kGy on the infrared absorption spectra of these glasses is also reported. The change in the glass structure due to the effect of composition is also discussed. It has been observed that irradiation of the glasses with the gamma rays increases the BO₃ groups and the non bridging oxygens which make the network loose.     

Bioactivity of SiO2-CaO-P2O5-Na2O glasses containing zinc-iron oxide

Glasses with composition x(ZnO,Fe₂O₃)(65 − x)SiO₂20(CaO,P₂O₅)15Na₂O (6 ≤ x ≤ 21 mol%) were prepared by melt-quenching technique. Bioactivity of the glasses was investigated in vitro by examining apatite formation on the surface of glasses treated in acellular simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma. Formation of bioactive apatite layer on the samples treated in SBF was confirmed by using Fourier transform infrared reflection (FTIR) spectroscopy, grazing incidence X-ray diffraction (GI-XRD) and scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer. Development of an apatite structure on the surface of the SBF treated glass samples as functions of composition and time could be established using the GI-XRD data. FTIR spectra of the glasses treated in SBF show features at characteristic vibration frequencies of apatite after 1-day of immersion in SBF. SEM observations revealed that the spherical particles formed on the glass surface were made of calcium and phosphorus with the Ca/P molar ratio being close to 1.67, corresponding to the value in crystalline apatite. Increase in bioactivity with increasing zinc-iron oxide content was observed. The results have been used to understand the evolution of the apatite surface layer as a function of glass composition and immersion time in SBF.     

Ultrasonic studies on alkali borate tungstate glasses

Longitudinal and shear ultrasonic wave velocities have been measured in different compositions of the glass system 20Li₂O-(80−x)B₂O₃-xWO₃ (0?x?12.5 mol%), at room temperature and at 4 MHz frequency. Elastic moduli, Debye temperature and Poisson's ratio have been obtained as a function of WO₃ content. Based on FTIR spectroscopy and theoretical bond compression model, quantitative analysis has been carried out in order to obtain more information about the structure of these glasses. The longitudinal ultrasonic wave velocity measurements showed a bend at about 2.5 mol% WO₃ content while shear ultrasonic wave velocity decreased monotonously with an increase of WO₃ content. Elastic moduli values decreased as WO₃ content increased from 0 to 2.5 mol%. Further increase of WO₃ beyond 2.5 mol% increased the elastic moduli values. It is suggested that these behaviours are mainly due to the presence of WO₃ in the network structure of these glasses as a network modifier when WO₃ content is between 0 and 2.5 mol%, and acts as a network former above 2.5 mol%.     

Meeting experimental challenges to physics of network glasses: Assessing the role of sample homogeneity

We introduce a Raman profiling method to track homogenization of Ge_xSe_100−x melts in real time, and show that 2 g melts reacted at 950 °C in high vacuum homogenize in 168 h on a scale of 10μm. Homogenization of melts is precursive to self-organization of glasses. In the present glasses, compositional variation of Raman active corner-sharing mode frequency of GeSe₄ units, molar volumes, and the enthalpy of relaxation at T_g, reveal the rigidity (x_c(1)=19.5(3)%) and the stress (x_c(2)=26.0(3)%) transitions to be rather sharp (Δx<0.6%). These abrupt elastic phase transitions are in harmony with rigidity theory and have a direct bearing on the physics of glasses.     

Optical characterization of Cu ion-doped zinc lead borate glasses

We have developed a new series of zinc lead borate (ZLB) glasses by varying ZnO content, to enhance UV transmission, in the chemical composition of xZnO-15PbO-(85−x)B₂O₃, where x=0, 5, 10, 15, 20, 25, 30, 35, 40 and 45 mol% ZnO. From the measurement of UV absorption spectra both the direct and indirect band gaps have been evaluated. Also different physical properties of a reference glass of 45ZnO-15PbO-40B₂O₃ have been studied. From the measurement of refractive indices at six different wavelengths, Cauchy's constants (A=1.578743209; and ) have been computed and a satisfactory correlation has been achieved between the theoretical and the experimental results. Absorption spectra of Cu²⁺(45−x)ZnO-15PbO-40B₂O₃ (where x=0.1, 0.2, 0.5 and 1.0 mol%) have shown two absorption bands at 428 nm (²B_1g→²E_g) and 777 nm (²B_1g→²B_2g). Emission spectra of (1.0 mol%) Cu²⁺:ZLB have revealed two emission transitions at 400 and 493 nm with excitations at 288 and 316 nm.     

Optical absorption and thermoluminescence studies on LiF-Sb2O3-B2O3 glasses doped with Ni ions

20LiF-(30−x)Sb₂O₃-50B₂O₃:xNiO glasses with the value of x (ranging from 0 to 1.0 mol% in steps of 0.2) were prepared. A number of studies, viz. differential scanning calorimetry, optical absorption, magnetic susceptibility and thermoluminescence, on these glasses were carried out as a function of nickel ion concentration. An anomaly has been observed in all the properties of these glasses when NiO concentration is about 0.6 mol%. The results of these studies were analysed in the light of different environments of nickel ions in the glass network.     

Preparation and study of magnetic properties of silico phosphate glass and glass-ceramics having iron and zinc oxide

The magnetic properties of 25SiO₂–50CaO–15P₂O₅–(10−x)Fe₂O₃−xZnO (where x=0, 2, 5 mol%) glass and glass-ceramics have been studied. These glasses are prepared by melt quench technique and heat treated at 800 °C for 6 h. Electron Spectroscopy for Chemical Analysis (ESCA) revealed that the fraction of non-bridging oxygen decreases with the increase in zinc oxide content. Evolution of crystalline phases in glass-ceramics has been studied by X-ray diffraction (XRD). The microstructure as seen by scanning electron microscopy (SEM) exhibits formation of nanosize particles. Effect of controlled heat treatment on magnetic properties was studied by means of a Superconducting Quantum Interference Device (SQUID) magnetometer. Mössbauer spectroscopy at room temperature was also carried out to determine the state of iron ions in glasses and glass-ceramics. Isomer shift values of the glasses suggest that Fe³⁺ and Fe²⁺ are in tetrahedral coordination. The analysis of the glass without ZnO shows about 58 wt% of total iron ions is in the Fe³⁺ state. The samples on heat treatment show improved magnetic properties due to the formation of magnetic nanoparticles. Magnetic studies revealed the relaxation of magnetic particles and the increase in saturation magnetization with addition of 2 mol% ZnO. Increase in ZnO content results in decrease in the strength of dipolar interactions.     

Structure and elastic properties of TeO2-BaF2 glasses

Binary tellurite (100−x)TeO₂-xBaF₂ glasses for different compositions of BaF₂ (x=8, 10, 12, 15, 18 and 20 wt%) have been prepared by rapid quenching method. The velocities and attenuation during the propagation of the ultrasonic waves in all glasses were measured using a transducer operated at a fundamental frequency of 5 MHz at room temperature. A progressive increase in BaF₂ content leads to a decrease in ultrasonic velocities and density, which is followed by an increase in attenuation. The existence of depolymerisation of Te co-ordination leads to the transformation of TeO₄ trigonal bipyramid units through TeO₃₊₁ polyhedron to TeO₃ trigonal pyramid units. This is responsible for the observed decrease in the measured and determined parameters with the addition of the modifier content.     

Thermoluminescence of B2O3-Li2O glass system doped with MgO

Lithium borate (LiB) glasses in the system (100−x)B₂O₃-xLi₂O with x=20, 30, 40, 50, 60 and 70 mol% were prepared. The glasses were doped with different concentrations of the order of 10⁻¹, 10⁻², 10⁻³, 10⁻⁴ and 10⁻⁵ of MgO and their thermoluminescent (TL) response was investigated. The irradiations were performed using γ rays from a ⁶⁰Co source in the dose range from 0.1 to 25 kGy. The material displayed good sensitivity for γ-rays and intensity of TL signals is dependent on γ-ray dose and Li₂O content. For each dose level and investigated temperature range (50-350 °C), exactly single isolated glow peak appears in the temperature range of 165-205 °C depending on both Li₂O concentrations and time of exposure. The shape of the glow peak has altered significantly with increase in the gamma ray dose or Li₂O concentrations. The glass composition with x=50 mol% doped with 10⁻³ mol% of MgO presented the best TL response. The results of the present study indicated that the recorded single and isolated high temperature peak is a good candidate for TL dosimetric investigations. This indicates that 50 B₂O₃-50Li₂O-doped with 10⁻³ mol% of MgO is possibly used as materials for radiation dosimetry in the dose range of 0.1-20 kGy.     

Luminescence spectra and optical properties of TeO2-WO3-Li2O glasses doped with Nd, Sm and Er rare earth ions

New tellurite glass series of the form (70-x)TeO₂-20WO₃-10Li₂O-xLn₂O₃, where x=0, 1, 3 and 5 mol% and Ln=Nd, Sm and Er, were prepared. Density of the prepared glasses was measured and molar volume was calculated. Luminescence spectra of the prepared glasses were measured at room temperature using a micro-Raman spectrometer. The obtained luminescence intensity ratio was correlated with the rare earth ion concentration, the short distance between the identical rare earth ions r(Ln-Ln) and the glass density. Optical properties like refractive index, molar refractivity and optical polarizability were theoretically calculated in order to interpret the dependence of these properties on the rare earth ion content.     

Structural investigation of bismuth borate glasses under the influence of γ-irradiation through ultrasonic studies

The ultrasonic velocity and attenuation measurements for different compositions of irradiated heavy metal oxide (HMO) borate glasses xBi₂O₃ (1−x) B₂O₃ (where x=0.25, 0.30, 0.35, 0.40, 0.45) has been investigated at room temperature (303 K) using pulse echo overlap method. The elastic moduli, Debye temperature, Poisson's ratio and other acoustical parameters have been obtained from experimental data. Structural changes after irradiation have been investigated by using FTIR spectroscopy and ultrasonic studies. As the changes are strongly dependent on the internal structure of the absorbing substance, in the present investigation ultrasonic velocities before and after γ-irradiation in bismuth borate glasses are measured as a function of composition, from which the structural changes in the network former B₂O₃ and modifier Bi₂O₃ due to irradiation are obtained.     

Nanoscale intrinsic heterogeneities in Ag-Ge-Se glasses and their correlation with physical properties

Ag-Ge-Se glass forming system is dominated by liquid immiscibility. Glasses in the Se-GeSe₂-Ag₂Se triangle may have different morphologies according to their composition. In this work inhomogeneous morphology is observed in Ag_x(Ge_ySe_1−y)_100−x bulk glasses with y = 0.20, 0.25 at.% fraction. Electron microscopy reveals that the scale of heterogeneity strongly depends on the sample composition. The physical properties of these glasses are also dependent on their composition and can be easily correlated to their morphology. Accordingly, the electric conductivity evolves from semiconducting to ionic conductivity whereas a percolation transition occurs in a narrow Ag concentration range.Mössbauer spectrometry let us to analyse the local order of these intrinsically heterogeneous glasses employing ⁵⁷Fe as a probe.     

Effect of Li2O content on physical and structural properties of vanadyl doped alkali zinc borate glasses

The effect of Li₂O content in vanadyl doped 20ZnO+xLi₂O+(30−x)Na₂O+50B₂O₃ (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO²⁺ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g_⊥-g_∥) and Dt reveals that their values vary non-linearly with Li₂O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect.     

Effects of SrO/ZnO on structure and properties of UV-transmitting borophosphosilicate glass

UV-transmitting borophosphosilicate glasses series, 2Al₂O₃−xSrO-(18−x)ZnO-33.3P₂O₅-16.7B₂O₃-30SiO₂ glasses with x=0-18 mol% were prepared and studied. The substitution of SrO for ZnO increases the density and the thermal expansion coefficient (α), but decreases the molar volume (V_m). The glass transition temperatures (T_g) and softening points (T_d) vary within a small range. The relative chemical durability was determined by measuring the weight loss of a polished glass sample after immersion in deionized water at 50 °C for 24 h, the chemical durability of the glasses increases when x≤9, and drops when x>9. With the increasing SrO content, the UV transmittance of the glasses decreases mildly. The compositional dependence of E_opt shows a decrease trend with increasing SrO content. The structural changes with the glass compositions were examined by FT-IR and Raman spectra.     

Electrical switching and thermal studies on Ge22Te78−xIx chalcohalide glasses: The effect of iodine on network-topology

Investigations on the electrical switching behavior and thermal studies using Alternating Differential Scanning Calorimetry have been undertaken on bulk, melt-quenched Ge₂₂Te_78−xI_x (3≤x≤10) chalcohalide glasses. All the glasses studied have been found to exhibit memory-type electrical switching. The threshold voltages of Ge₂₂Te_78−xI_x glasses have been found to increase with the addition of iodine and the composition dependence of threshold voltages of Ge₂₂Te_78−xI_x glasses exhibits a cusp at 5 at.% of iodine. Also, the variation with composition of the glass transition temperature (T_g) of Ge₂₂Te_78−xI_x glasses, exhibits a broad hump around this composition. Based on the present results, the composition x=5 has been identified as the inverse rigidity percolation threshold at which Ge₂₂Te_78−xI_x glassy system exhibits a change from a stressed rigid amorphous solid to a flexible polymeric glass. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy () of Ge₂₂Te_78−xI_x glasses at x=5, which is suggestive of a thermally reversing window at this composition.