Production and properties of high purity TeO2− WO3−(La2O3, Bi2O3) and TeO2− ZnO−Na2O−Bi2O3 glasses

TeO₂–WO₃ (TW), TeO₂–WO₃–La₂O₃ (TWL), TeO₂–WO₃–La₂O₃–Bi₂O₃ (TWLB) and TeO₂–ZnO–Na₂O–Bi₂O₃ (TZNB) glasses were produced by high-purity oxide mixtures melting in platinum or gold crucible at 800 °C in the atmosphere of purified oxygen. The total content of Cu, Mn, Fe, Co and Ni impurities was not more than 0.1–0.5 ppm wt in the initial oxides and glasses. The stability of TZNB glasses to crystallization, characterized by (T_x ? T_g) value more than 150 °C, was demonstrated by DSC measurements at heating rate 10 K/min. In the case of La₂O₃-containing glasses the thermal effects of both crystallization and fusion of the crystallized phases were not observed. The hydroxyl groups absorption coefficients of pure tellurite glasses at the maximum of the absorption band (λ ~ 3 μm) were in the region of 0.012–0.001 cm^?1. The optical absorption losses, measured by the laser calorimetry method at λ = 1.56 and 1.97 μm, did not exceed 100 dB/km.     

Magnetic behavior and microstructure of x%V2O5·(100−x)%As2O3 glasses

The magnetic properties and microstructure of x%V₂O₅·(100−x)%As₂O₃ glasses with x varying in the range 40 to 90 mol% were investigated in order to elucidate their magnetic ordering. Weak antiferromagnetic interactions between V⁴⁺ ions were observed. Glasses with x ⩾ 60 separated into two glassy phases. The effect of microstructure on magnetic properties of these glasses was investigated. Phase separation increases with increasing V₂O₅ content and produces a broadening of the EPR line width of glasses with high vanadium content (x > 70). The c = V⁴⁺/V_total ratio of x%V₂O₅·(100−x)%As₂O₃ glasses, determined from EPR and chemical analysis, are considerably greater than those usually reported for x%V₂O₅·(100−x)%P₂O₅ glasses.     

Band gap determination by absorption spectrum fitting method (ASF) and structural properties of different compositions of (60−x) V2O5–40TeO2–xSb2O3 glasses

Glasses with compositions (60?x) V₂O₅–40TeO₂–xSb₂O₃ with 0 ? x ? 10 (in mol%) have been prepared using usual melt quenching method. The position of the absorption edge and hence the values of the optical band gap was found to depend on the glass composition. Using the Tauc model, the absorption spectrum fitting method (ASF) was employed to obtain the optical band gap. This method requires only the measurement of the absorbance spectrum of the sample. For each sample, the width of the band tail was determined. Also, the density and glass transition temperature values indicate that the rigidity and packing of the samples increase with increase in Sb₂O₃ concentration.     

Raman spectroscopy studies of xNa2S+(1−x)B2S3 glasses and polycrystals

The Raman spectra of binary xNa₂S+(1−x)B₂S₃ glasses and polycrystals have been measured for the first time and are used to develop a structural model of the sodium thioborate glasses. The Raman spectra confirm our previous infrared (IR) experimental conclusions that the structure of vitreous (ν-B₂S₃) is comprised of B3(0) groups and six-membered rings. It was also found that as sodium sulfide is added to the glass in the low alkali (x<0.35) glass forming region, the B4 groups are formed at the expense of the B3(0) groups first and then from the six-membered ring groups. The Raman spectra are also consistent with the presence of a pyramidal structural arrangement of B4 groups with trigonally coordinated sulfur atoms. This structure could explain the existence of the super-stoichiometric amounts of B4 groups found using nuclear magnetic resonance (NMR). Glasses in the high alkali region (0.50<x<0.80) progressively change from being comprised of metathioborate rings to being comprised of B3(3) groups. The Raman spectra also confirms the IR spectra which saw no evidence of B3(2) groups in these sodium thioborate glasses.     

Bi precipitates in Na2O–B2O3 glasses

Bi particles of different sizes were produced in Na₂O–B₂O₃ glasses by melt quenching and heat treatment technique. Melting temperature of Bi particles was measured by differential scanning calorimetry and X-ray diffraction. Measured melting temperatures of Bi particles are lower than bulk Bi melting temperature. Results of transmission electron microscopy were analyzed for the dependence of melting temperature on particle radius. The pressure and surface energy effect on melting temperature is estimated. The melting behavior of Bi particles in Na₂O–B₂O₃ glasses depends on the difference in the interfacial energies between the solid particle/glass and liquid particle/glass, and liquid particle/glass, σ_sm−σ_lm, which is estimated to be 255×10⁻³ J m⁻².     

Mixed alkali effect in physical and optical properties of Li2O–Na2O–WO3–B2O3 glasses

Glasses with composition xLi₂O-(30 ? x)Na₂O–10WO₃–60B₂O₃ (where x = 0, 5, 10, 15, 20, 25 and 30 mol%) have been prepared using the melt quenching technique. In the present work, the mixed alkali effect (MAE) has been investigated in the above glass system through density and modulated DSC studies. The density and glass transition temperature of the present gasses varies non-linearly, the exhibiting the mixed alkali effect. From the optical absorption studies, the values of direct optical band gap, indirect optical band gap energy (E_o) and Urbach energy(ΔE) have been evaluated. The values of E_o and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The electronic polarizability of oxide ions, optical basicity and the Yamashita–Kurosawa's interaction parameter have been examined to check the correlation among them and bond character. Based on good correlation among electronic polarizability of oxide ions, optical basicity and the Yamashita–Kurosawa's interaction parameter, the present Li₂O–Na₂O–WO₃–B₂O₃ glasses were classified as normal ionic (basic) oxides.     

Optical properties and structure of amorphous films Agx(As0.33S0.67−ySey)100−x

As₃₃S_67−ySe_y, where y = 0, 16.75, 33.5, 50.25 and 67, amorphous thin films were prepared by a vacuum thermal evaporation technique. The films with known silver concentrations and good optical quality were prepared by thermal vacuum evaporation of a silver film on the top of As₃₃S_100−ySe_y films with sequential step-by-step optically- and thermally-induced diffusion and dissolution (OIDD) of silver. The range of silver content was x = 0–25 at.%. The kinetics of OIDD of silver were measured optically by monitoring the change of thickness of the undoped part of the chalcogenide during broadband illumination. Compositions of the reaction products have been determined by scanning electron microscope with energy-dispersive X-ray microanalyser EDS. Optical properties $(T\text{,}n\text{,}{E}_{\text{g}}^{\text{opt}})$ of thin films were measured and/or calculated by the Swanepoel method [R. Swanepoel, J. Phys. E: Sci. Instrum. 16 (1983) 1214]. The refractive index increase with increasing silver and selenium concentration has been shown. The difference of the refractive index (Δn) between undoped and silver doped films was ∼0.4 and between As₃₃S₆₇ and As₃₃Se₆₇ was films ∼0.42. Non-linear indices of refraction were estimated according to Tichy’s formula [H. Ticha, L. Tichy, J. Optoel, Adv. Mat. 4 (2002) 381]. The values of non-linear refractive index grew with increasing silver and selenium content. The difference of optical bandgap, $\mathrm{\Delta }{E}_{\text{g}}^{\text{opt}}$, between undoped As₃₃S₆₇ and fully doped films with Ag and Se was ∼1 eV. Raman spectroscopy showed a decrease in S–S or Se–Se bonds with increasing silver content.     

Structure and properties of ceramic solid solutions Li x Na1 − x Ta y Nb 1 − y O3 (x = 0–0.05, y = 0–0.04)

The structure of Li_0.03Na_0.97Ta _y Nb_{1 ? y} O₃ ceramic solid solutions and the processes of its disordering with a change in composition and temperature have been studied by full-profile X-ray diffraction analysis and Raman spectroscopy. It was established that at room temperature the structure of Li_0.03Na_0.97Ta_0.05Nb_0.95O₃ solid solutions is close to the NaNbO₃ structure and has a space group P21ma with four formula units per unit cell. It was shown that the oxygen octahedra in the Li _x Na_1?x Ta_0.1Nb_0.9O₃ solid solutions (0, 0.15, 0.03, 0.04, 0.05) are slightly distorted and their geometry is identical to that of octahedra in the NaNbO₃ structure. The temperature dependence of the intensities of lines in the Raman spectrum of Li_0.03Na_0.97Ta_0.4Nb_0.6O₃ solid solutions corresponding to vibrations of Li⁺ and Na⁺ cations in the cuboctahedral structural voids revealed a strong disordering in the alkali metal sublattice at a temperature above 322°C. This may indicate the essential stepwise increase in the Li⁺ cation mobility and may result in a change in the kinetic and energetic characteristics of ion charge transport.     

Structural role and coordination environment of Fe in Fe2O3–PbO–SiO2–Na2O composite glasses

The structural role, coordination geometry and valence of Fe in a series of Fe₂O₃–PbO–SiO₂–Na₂O glasses are studied by means of Fe-K-NEXAFS and EXAFS spectroscopies. Parameters for the study are the concentration of the Fe and Pb-oxides, the SiO₂/Na₂O ratio and the cast temperature. The EXAFS and NEXAFS results reveal that the role of Fe³⁺ depends on the concentration of Fe₂O₃. More specifically, in most of the studied quaternary systems, the Fe³⁺ ion is a glass former, i.e. the Fe atoms belong to FeO₄ tetrahedra that participate in the formation of the glassy network. The role of Fe as an intermediate oxide is identified only in one sample with 20 wt% Fe₂O₃, where ～80 at.% of the Fe atoms are tetrahedrally coordinated with O atoms, while the remaining ～20 at.% of the Fe atoms occupy octahedral sites. It is also revealed that the tetrahedral coordination of Fe in the vitreous matrix is destroyed when a number of parameters is altered, such as the T_cast, the (Fe + Si)/O and the SiO₂/Na₂O ratio.     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.     

Dielectric properties,conductivity, UV–visible and infrared spectroscopy of PbO P2O5 NaF glasses containing WO3

Homogeneous (50P₂O₅–(30 ? x)PbO–20NaF–xWO₃ where x = 0.0, 5, 10 and 15 mol%) glasses were synthesized using a melt-quenching method. The short range structures of the phosphate samples were examined by Fourier transform infrared spectroscopy. The infrared spectral studies have pointed out the existence of conventional PO₄, WO₄ and WO₆ structural units in the glass network, the number of WO₄ tetrahedra decreases as WO₃ concentration increases. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range of 190–1100 nm. The values of the optical band gap E_op for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of the dielectric constant have been determined. The type of electronic transitions in the present glass system is indirectly allowed and the high values for the refractive index and dispersion are recorded due to the high polarizability of tungsten ions. The results of refractive indices as determined reveal the homogeneity of samples and were found to depend on the glass composition. The electrical properties of the glasses were investigated by ac conductivity from 0.12 to 100 kHz for temperatures ranging from room temperature to 600 K. The study of dielectric properties suggested increase in the insulating character of the glass system with increase in the content of WO₃. The ac conductivity in the high temperature region seems to be connected mainly with the polarons involved in the process of transfer from W⁴⁺ to W⁵⁺ ions.     

Growth and characterization of lead-free Ba(1−x)CaxTi(1−y)ZryO3 single crystal

A lead-free Ba_(1?x)Ca_xTi_(1?y)Zr_yO₃ (BCZT) single crystal (x=0.08, y=0.26) was grown by the Czochralski (CZ) method in a mixed flux of TiO₂ and ZrO₂. The composition of as-grown BCZT was analyzed by electron probe micro-analysis. The structure, dielectric properties and phase transition were investigated at different temperatures. The X-ray diffraction results confirmed that the structure of the as-grown BCZT crystal was cubic both at 25 °C and 500 °C. The temperature dependence of the dielectric constant and Raman spectra characterization revealed that there was a phase transition from cubic to tetragonal, which happened between 200 K and 250 K. With increasing frequency, the Curie temperature shifted towards high temperature.     

Electromechanical and electro-optic properties of xBiScO3–yBiGaO3–(1−x−y)PbTiO3 single crystals

Single crystals in the xBiScO₃–yBiGaO₃–(1−x−y)PbTiO₃ (BS–BG–PT) system were grown by the high temperature solution method using Pb₃O₄ and Bi₂O₃ as the flux. The dielectric permittivity (ε_r) at room temperature for unpoled tetragonal crystals was determined to be 500–600 with dielectric loss tangents less than 0.3%. The Curie temperature was found to be around ∼420–450°C, with a dielectric maximum, exhibiting relaxor behavior. The longitudinal piezoelectric coefficient (d₃₃) was found to be ∼300 pC/N for 〈0 0 1〉 oriented tetragonal crystals with electromechanical coupling factor (k₃₃) of 75%, with a shear mode, d₁₅∼290 pC/N and k₁₅∼45%, lateral mode, d₃₁∼−55 pC/N and k₃₁∼−37%. The remnant polarization (P_r) was 46 μC/cm² with a coercive field (E_c) of 43 kV/cm at 1 Hz and DC field of 60 kV/cm. The linear electro-optic (E-O) coefficients of poled crystals determined using an automated scanning Mach–Zehnder interferometer method at room temperature and wavelength of 632.8 nm were r₃₃=36 and r₁₃=4 pm/V, respectively.     

Micro-structural studies of GeSe2–Ga2Se3–MX (MX = CsI and PbI2) glasses using Raman spectra

Microstructure of the chalcohalide glasses: GeSe₂–Ga₂Se₃–CsI and GeSe₂–Ga₂Se₃–PbI₂ ternary system were investigated by Raman spectra, lifetime of Dy³⁺ infrared emission and glass transition temperature (T_g). The evolution of the Raman spectra shows that the fundamental structural groups of these studied glasses consist of [Ge(Ga)Se₄] tetrahedral and some complex structure units [Ge(Ga)I_xSe_4?x](x = 1–4). The x value varied when the different iodide was added in Ge–Ga–Se matrix. For GeSe₂–Ga₂Se₃–CsI glasses, the [Ge(Ga)I_xSe_4?x](x = 1–4) mixed-anion tetrahedral and [Ga₂I₇]^? units occurred. For GeSe₂–Ga₂Se₃–PbI₂ glasses, the [Ge(Ga)I₂Se₂], [Ge(Ga)I₃Se] units can be formed. The changes of Dy³⁺ infrared emission lifetime and T_g support the results. Additionally, [PbI_n] structural units will be formed in GeSe₂–Ga₂Se₃–PbI₂ glasses due to high form-ability of these units when the PbI₂ content is high.     

Structural role of MgO and PbO in MgO–PbO–B2O3 glasses as revealed by FTIR; a new approach

FTIR spectra of three MgO–PbO–B₂O₃ glass series have been analyzed. There is a decrease in the fraction N₄ of four coordinated boron with increasing the MgO content, at the expense of PbO. A new technique has been presented to make use of the N₄ data and follow the change in the modifier and former fractions of PbO and MgO. These fractions change markedly, at different rates, with the glass composition. The fraction of modifier MgO is always less than the MgO content, which suggests a former role of this oxide in the studied glasses. The ability of the glass to include MgO increases with increasing PbO content.