Electrical and dielectric properties of MnF2–ZnF2–NaPO3 glasses

Direct electrical conductivity and dependencies of complex electrical modulus vs. temperature and frequency have been measured on glasses from the MnF₂–ZnF₂–NaPO₃ system. These glasses are sensitive to atmospheric humidity and as a consequence, the electrical conductivity increases up to temperature of 50 °C. A hydrated layer is created by the effect of water and leads to the significant increase of the electrical conductivity in the case of 0MnF₂–20ZnF₂–80NaPO₃ glass. This behavior is governed by Arrhenius relation where the values of activation energy are increasing and values of the electrical conductivity are decreasing with the amount of MnF₂. Dielectric measurements show that a heterogeneous phase is formed in the bulk of glasses. This may be seen when plotting complex electrical modulus in the complex plane. The records made by the light microscope confirmed the occurrence of the other phase in the bulk of glasses.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Optical properties of new low-phonon SnF2–PbF2–ZnF2 glasses

New fluoride glasses were developed in the SnF₂–PbF₂–ZnF₂ system. Additions of 5 mol% of CsCl or 6–15 mol% of AlF₃ were found to stabilize the glass formation. The IR absorption of the glasses and the optical properties of the europium ions doped in the glasses were compared with those of a fluorozirconate glass as a representative fluoride glass. The IR spectra showed that the new glasses have the peak of the phonon energy at 400 cm⁻¹, which is about 100 cm⁻¹ lower than that of the fluorozirconate glass. The results of the fluorescence measurement of the europium ions revealed that the multi-phonon relaxation rate in these glasses is smaller than that in the fluorozirconate glass.     

Spectroscopic properties and ab initio calculations on the structure of erbium–zinc-borate glasses and glass ceramics

Glasses in the (Er₂O₃)_x·(B₂O₃)_(60 ? x)·(ZnO)₄₀ system (0 ≤ x ≤ 15 mol%) have been prepared by the melt quenching technique. X-ray diffraction, FTIR spectroscopy, UV-VIS spectroscopy and ab initio calculations studies have been employed to study the role of Er₂O₃ content on the structure of the investigated glass system.X-ray diffraction and infrared spectra of the glasses reveal that the B–O–B bonds may be broken with the creation of new non-bridging oxygen ions facilitating the formation of Er–O–B linkages. The excess of oxygen can be accommodated in the network by the conversion of sp² planar [BO₃] units to the more stable sp³ [BO₄] tetrahedral structural units. The linkages of the [BO₄] structural units can polymerize in [B₃O₉]^? 9 cyclic trimeric ions which will produce the ErBO₃ crystalline phase. An increase of the efficiency corresponding to the ⁴I_15/2 state to ⁴I_11/2 state (4f–4f) transitions of Er^+ 3 ions was observed for the erbium oxide richest glasses.Ab initio calculations on the structure of the matrix network show the thermodynamic instability of the [BO₄], [ZnO₄] and [Zn₄O] structural units. Formation of three-coordination oxygens was necessary to compensate shortage of oxygens from zinc ions.     

Effects of Fe2O3 replacement of ZnO on elastic and structural properties of 80TeO2–(20 − x)ZnO–xFe2O3 tellurite glass system

Ternary tellurite glasses with the chemical formula 80TeO₂–(2 ? x)ZnO–xFe₂O₃ (x = 0–15 mol%) have been prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5 MHz and Fourier transform infrared (FTIR) spectroscopy, respectively. Both longitudinal and shear velocity showed a large increase of 3.40% and 4.68%, respectively, at x = 5 mol% before a smaller increase for x > 5 mol%. Interestingly, longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young's modulus (E) recorded similar trends with increase in Fe₂O₃. The initial large increases in shear and longitudinal velocity and related elastic moduli observed at x = 5 mol% are suggested to be due to structural modification which enhances rigidity of the glass network. FTIR analysis showed increase in bridging oxygen (BO) as indicated by the relative intensity of the TeO₄ assigned peaks and increase in intensity of the FeO₆ assigned peak (~ 451 cm^? 1) which indicates that Fe acts as a modifier in the glass network. The increase in rigidity of the glass system is suggested to be due to the increase of BO together with the formation of strong covalent FeO bond. Quantitative analysis based on the bulk compression and ring deformation models showed that the k_bc/k_exp value decreased gradually from 2.41 (x = 0 mol%) to 2.02 (x = 15 mol%) which infers that the glass system became a relatively more open 3D network as Fe₂O₃ was increased.     

Nucleation and growth of needle-like fluorapatite crystals in bioactive glass–ceramics

The nucleation behaviors of glass–ceramics with different Ca–mica (Ca_0.5Mg₃AlSi₃O₁₀F₂)/fluorapatite ratios were investigated. By using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscope with an energy dispersive spectrometer (SEM/EDS), the effect of CaO and P₂O₅ addition on the nucleation behaviors was studied. Results showed that the addition of CaO and P₂O₅ promoted nucleation process and led to the formation of different nucleation phases. After further heat treatment, Ca₅(PO₄)₃F crystals were of needle-like morphology, instead of particle-like reported in previous studies. This can be attributed to the one-dimensional rapid growth of fluorapatite along the c-axis. The values of the Avrami parameter, n, and the dimensionality of crystal growth, m, are found to be 2 and 1, respectively, which indicated that the bulk nucleation is the dominant mechanism in crystallization, and one-dimensional growth of fluorapatite is preferred. Since needle-like fluorapatite crystals are of the same morphology to hydroxyapatites in human bones, the glass–ceramics thus prepared show excellent bioactivity in vivo.     

Synthesis and bioactive properties of macroporous nanoscale SiO2–CaO–P2O5 bioactive glass

A macroporous nanoscale bulk bioactive glass (SiO₂–CaO–P₂O₅ system) was prepared by sol–gel co-template method. Porosimeter analysis showed that the as-synthesized bioactive glasses (BGs) had a porosity of 85% and exhibited a multimodal pore size distribution, nanopores (10–40 nm) and macropores (100 nm–10 μm). Morphological and structural characterizations showed the pores were interconnected with pore walls of about 250 nm in width and 1 μm in length. In vitro bioactivity test indicated that the as-synthesized bulk BGs exhibited faster apatite layer formation capability than the conventional sol–gel BGs. Additionally, the deposited layer was identified as hydroxycarbonate apatite, which is similar to the inorganic part of human bone.     

Preparation of lithium ion conducting glasses and glass–ceramics for all-solid-state batteries

Highly lithium ion conducting glasses and glass–ceramics were prepared by a mechanical milling technique in the Li₂S-based sulfide and oxysulfide systems. The Li₂S–P₂S₅ glass–ceramics showed ionic conductivity as high as 3.2 × 10^?3 S cm^?1 at room temperature. All-solid-state batteries using these sulfide-based materials as a solid electrolyte showed excellent charge–discharge performance with high capacity and high cycleability. The cells with the combination of the SnS–P₂S₅ glassy electrode and the Li₂S–P₂S₅ glass–ceramic electrolyte worked as a secondary battery, which was a first step of glassy monolithic cells with a common glass network.     

Single-crystal growth of Ti–Nb–Ta–Zr–O alloys and measurement of elastic properties

Single crystals of β-type Ti alloy system Ti–Nb–Ta–Zr–O have been grown successfully in an Ar gas flow by a floating zone method. The growth orientations were determined approximately by using seed crystals with the desired orientations. The various growth conditions were realized by choosing the gas purity, the gas flow rate, and the growth rate as variables. Composition analysis of the grown crystals was done to check any variation from the values of the raw material along with the bulk homogeneity, followed by measurements of the lattice parameter and the hardness, which provides the following results: (1) the composition of oxygen varies with respect to the flow rate, or is increased as the purity is degraded, (2) the lattice parameter is increased with increasing composition of oxygen, (3) which is also the case with the hardness. Measurements of Young's moduli were performed to investigate the elastic properties. The results indicate that the crystals exhibit the anisotropy which was expected previously. The elastic constants were estimated from the moduli, giving the ideal stress 1.7–1.9 GPa which is on a level with the real strength. Additionally, the tensile stress–strain curve for the crystallographic direction 〈1 1 0〉 exhibited nonlinear elasticity and hysteresis.     

Crystallization of bismuth oxide nano-crystallites in a SiO2–PbO–Bi2O3 glass matrix

SiO₂–PbO–Bi₂O₃ glasses having the composition of 35SiO₂–xPbO–(65 ? x)Bi₂O₃ (where x = 5, 20 and 45; in mol%) have been prepared using the conventional melting and annealing method. Differential scanning calorimetry (DSC) was employed to characterize the thermal behavior of the prepared glasses in order to determine their crystallization temperatures (T_cr). It has been found that T_cr decreases with the decrease of Bi₂O₃ content. The amorphous nature of the prepared glasses as well as the crystallinity of the produced glass–ceramics were confirmed by X-ray powder diffraction (XRD) analysis. SiPbBi₂O₆ glass nano-composites, comprising bismuth oxides nano-crystallites, were obtained by controlled heat-treatment of the glasses at their (T_cr) for 10 h. Transmission electron microscopy (TEM) of the glass nano-crystal composites demonstrates the presence of cubic Bi₂O₃ nano-crystallites in the SiPbBi₂O₆ glass matrix. Nano-crystallites mean size has been determined from XRD line width analysis using Scherrer's equation as well as from TEM; and the sizes obtained from both analyses are in good agreement. These sizes varied from about 15 to 170 nm depending on the chemical compositions of parent glasses and, consequently, their structure. Interestingly, replacement of the Bi₂O₃ by PbO in the glass compositions has pronounced effect on the nature, morphology and size of the formed nano-crystallites. Decrease of the Bi₂O₃ content increases the size of the nano-crystallites, and at the lowest Bi₂O₃ extreme, namely 20 mol%, introduces minority of the monoclinic Bi₂O₄ in addition to the cubic Bi₂O₃. The crystallization mechanism is suggested to involve a diffusion controlled growth of the bismuth oxide nano-crystallites in the SiPbBi₂O₆ glass matrix with the zero nucleation rate.     

Electrical and dielectric properties of glass system NaPO3–KHSO4

Glass samples have been prepared in the NaPO₃–KHSO₄ binary system with the classical melting, casting and annealing steps. Electrical and dielectrical properties of glass samples were studied. Measurements of DC and AC conductivity and complex electrical permittivity of xNaPO₃–(100 ? x)KHSO₄ glass system were carried out at temperatures ranging from room temperature to temperature located 15 °C below glass transition temperature T_g. Results showed that changes of NaPO₃ concentration considerably affect values of observed parameters. DC conductivity of glass increases as NaPO₃ concentration grows until concentration x = 60. However, beyond this value a sharp decrease of DC conductivity was observed. In addition relaxation times showed abrupt changes at concentration x = 60, corresponding to the lowest relaxation times at the temperature 90 °C.     

Preparation and third-order optical nonlinearity of glass ceramics based on GeS2–Ga2S3–CsCl pseudo-ternary system

Chalcohalide glass-ceramics based on GeS₂–Ga₂S₃–CsCl pseudo-ternary system were prepared by heat treatment method. X-ray diffraction and scanning electron microscope studies confirmed the formations of Ga₂S₃ and GeS₂ phase grains with sizes of 2–5 and 80 nm, respectively. Z-scan technology was employed to investigate the third-order nonlinear optical characteristics of both precursor glass and its glass ceramics at 800 nm. The results show that nonlinear refractive index n₂ as well as nonlinear absorption coefficient β increase after heat treatment, which is due to quantum effects, and the largest n₂ of the glass ceramics is 4.3 × 10^? 11 esu which is 4 times larger than that of the host.     

Dielectric and optical properties of surface crystallized TeO2– LiNbO3 glasses

Glasses with composition (100 − x) TeO₂–x LiNbO₃ (10⩽x⩽50) were prepared by conventional melt-quenching. The glass-formation ability, dielectric and optical properties of these glasses were studied. LiNbO₃ microcrystallites were directly precipitated on the surface of the glass, with the composition 50 TeO₂ – 50 LiNbO₃, by a single step heat treatment. The polar nature and second-order optical non-linearity of the transparent surface crystallized glasses are manifested in their strong pyroelectric response, ferroelectric hysteresis and intense second harmonic generation of 1064 nm wavelength radiation.     

Effect of lead oxide on optical properties of Dy3+ ions in PbO–H3BO3–TiO2–AlF3 glasses

The effect of lead oxide (PbO) on optical properties of Dy³⁺-doped PbO–H₃BO₃–TiO₂–AlF₃ (LBTAFDy) glasses is investigated. The LBTAFDy glasses were prepared with different PbO contents ranging from 30 to 60 mol%. The Judd–Ofelt intensity parameters (Ω_{λ = 2, 4, 6}) are obtained by the least square fit analysis. It is found that the Ω₂ parameter and yellow-to-blue intensity ratio (Y/B) of the Dy³⁺ emission depend on the PbO content in LBTAFDy glass. The structural asymmetry around the Dy³⁺ ion and the DyO covalency are responsible for the changes in Ω₂ parameter and Y/B ratio. The variation of decay time of ⁴F_9/2 emission level with the PbO content also supports the changes in structural asymmetry and DyO covalency in LBTAFDy glass.     

The effect of composition and temperature on the amount and type of nanoferrite particles inserted in Fe2O3–ZnO–MgO–SiO2 glass–ceramics

Glass–ceramics with the composition 2Fe₂O₃.1ZnO.1MgO.96SiO₂ [4ZnMgFe] and 2Fe₂O₃.2ZnO.3MgO.93SiO₂ [7ZnMgFe] (mol%) were prepared using the sol–gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron diffraction (ED) and Mössbauer spectroscopy (MS) were used to investigate the glass–ceramics structure. The samples contain ferrite nanoparticles embedded in a glass matrix. However, zinc ferrite nanoparticles seems to be the preferential crystalline phase formed. The amount of ferrite particles depends on treatment temperature and sample composition. The Mössbauer spectroscopy measurements show that ferrite nanoparticles can exhibit a ferrimagnetic behaviour combined with superparamagnetism.     

Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO₂–xBi₂O₃–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi₂O₃ content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi₂O₃ content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi_0.864Te_0.136O_1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.     

Microstructural characteristics and crystallization of CaO–P2O5–Na2O–ZnO glass ceramics prepared by sol–gel method

Porous phosphate-based glass ceramics prepared by the sol–gel method were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential thermal analysis (DSC). The 48CaO–45P₂O₅–2ZnO–5Na₂O glassy system can remain fully amorphous up to 550 °C. After heat treated at 650 °C, the obtained porous bodies consisted of dense struts and macropores where β-Ca₂P₂O₇ and Na₂CaP₂O₇ phases crystallized from the glass matrix. When treated at 750 °C, Ca₄P₆O₁₉ and NaZn(PO₃)₃ precipitated homogeneously as new phases among the residual glass matrix. The material was assessed by soaking samples in phosphate-based buffer solution (PBS) solution to determine the solubility and observe apatite formation.     

Corrosion of electrocast AZS refractories by CAS glass–ceramics melting

Extensive corrosion experiments on electrocast alumina–zirconia–silica (AZS) refractories by molten CaO–Al₂O₃–SiO₂ (CAS) and Na₂O–CaO–SiO₂ (NCS) glasses were carried out at various temperatures under static condition. The features and mechanism of the corrosion were compared and analyzed. The changes of microstructure and phase composition of refractories in the course of the melt corrosion were also studied. X-ray diffraction (XRD), scanning electron microscope (SEM) and chemical analysis were used to characterize the corroded refractory materials and reacted melts. The reasons of alumina–zirconia–silica bricks corroded are the meltdown of their own composition, penetration or permeation of alkali oxide in the glass melt and scouring of the glass melt. The results show that the refractories resistance against corrosion of the oxides like Na₂O, K₂O or CaO is weak, and that the corrosion mechanism of NCS/AZS is different from that of CAS/AZS. In a static condition, CaO–Al₂O₃–SiO₂ melts corroded alumina–zirconia–silica brick more severely than Na₂O–CaO–SiO₂. The result provides useful reference to a prospective selection of refractory materials in glass and glass–ceramics manufacture.     

Glass formation and third-order optical nonlinear properties within TeO2–Bi2O3–BaO pseudo-ternary system

Tellurite glasses from TeO₂–Bi₂O₃–BaO pseudo-ternary system were prepared using a conventional melt-quenching method and its glass-forming region was determined. A series of glasses were selected and their third-order optical nonlinearities (TONL) were measured by employing the Z-scan method at a wavelength of 800 nm with femtosecond laser pulses. The results showed that glass former Te⁴⁺ ions exhibited positive influences on the TONL and glass modifiers Ba²⁺ ions behaved similarly; low concentrated Bi³⁺ ions as glass modifiers weakened the nonlinearities, but an excess amount of Bi³⁺ behaved oppositely. FTIR measurements demonstrated that chemical bonds especially Te–O_eq vibrated at a high energy level remarkably promoted the TONL susceptibility χ⁽³⁾, and the glass sample with the highest Bi₂O₃ content exhibited the largest χ⁽³⁾ value which was due to the presence of BiO₃ polyhedra.