Correlation Between Crystallization Behavior and Network Structure in GeS2–Ga2S3–CsI Chalcogenide Glasses

Diagram of the phase transformation behavior of GeS₂–Ga₂S₃–CsI glasses is realized in this article and the structure‐property dependence of the chalcogenide glasses is elucidated using differential scanning calorimetry and Raman spectroscopy. We observe the compositional threshold of crystallization behavior locates at x = 6–7 mol% in (100?x)(0.8GeS₂–0.2Ga₂S₃)–xCsI glasses, which is confirmed by the thermodynamic studies. Structural motifs are derived from the Raman result that [Ge(Ga)S₄], [S₂GeI₂], [S₃GaI], and [S₃Ga–GaS₃] were identified to exist in this glass network. Combined with the information of structural threshold, local arrangement of these structural motifs is proposed to explain all the experimental observations, which provides a new way to understand the correlation between crystallization behavior and network structure in chalcogenide glasses.     

Glass Formation and Characterization Studies in the TeO2–WO3–Na2O System

Glass formation behavior of the TeO₂–WO₃–Na₂O system was studied by using conventional melt‐quenching technique. A wide glass formation range was determined for the first time in the literature and thermal, physical, and structural characterization of sodium‐tungsten‐tellurite glasses were realized using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. Glass transition (T_g) and crystallization (T_c/T_p) temperatures, glass stability (?T), density (ρ), molar volume (V_M), oxygen molar volume (V_O), and oxygen packing density (OPD) values and structural transformations in the glass network were investigated according to the equimolar substitution of TeO₂ by Na₂O+WO₃ and changing Na₂O or WO₃ at constant TeO₂.     

Correlating Structure with Threshold Behavior of Chalcogenide Glasses Within Ge–Sn–Se Ternary System

A systematic investigation of the optical and structural properties of chalcogenide glasses in Ge–Sn–Se ternary system is presented. We have found a threshold behavior of optical property, namely, existence of transitional composition of the Ge–Sn–Se glasses, with progressive replacement of Se by Sn. Calculation of mean coordination number indicates that the transition‐like feature of optical property is associated with the evolution of chemical ordering of the Ge–Sn–Se network. Analysis of Raman spectra of the glasses explains that the interaction between Se–Se bonds, Sn(Se_1/2)₄ tetrahedra, and Sn–Sn homopolar bonds is the origination of such optical phenomenon.     

The Effect of PbS on Crystallization Behavior of GeS2‐Ga2S3‐Based Chalcogenide Glasses

Glass‐ceramics of PbS‐doped 80GeS₂·20Ga₂S₃ were fabricated by heat treatments of base glasses at T_g+30°C for different durations. They exhibited improved mechanical properties such as hardness and resistance to crack propagation, and meanwhile retained their excellent infrared transmission. X‐ray diffraction and Raman results indicated that Ga₂S₃ and GeS₂ crystals were precipitated inside glassy matrix. The crystallization kinetics of base glass was investigated using differential scanning calorimetry under nonisothermal conditions. Compared with the previous work concerning on 80GeS₂·20Ga₂S₃ glass, there exists some different features of crystallization behavior. Such variation is discussed and correlated with the network structure and crystallization kinetics in this glass system.     

A Comparative Study of Purification Routes for As2Se3 Chalcogenide Glass

Chalcogenide glasses have been widely studied due to their extraordinary transparency in the mid-infrared region. Their transparency, combined with tailorable thermo-mechanical properties, makes them ideal candidates for various optic applications. Extrinsic impurities within the glass matrix can impede their integration in components where low optical loss is a requirement. Additionally, chalcogenide materials typically exhibit low mechanical strength due to the comparatively weaker average bond strength of constituents. Here, we report findings of efforts to explore various purification methods on As₂Se₃ glasses to improve their optical and mechanical properties. These methods involve oxides removal by thermal treatment of the reagents, and addition of AlCl₃ impurity-getters in the melt followed by distillation. We show that these techniques yield very effective results on the removal of hydroxyls, water, and oxide impurities. We also observe a recurrent increase in the Se-H vibrational band, with the concentration of the Se-H species escalating to several tens-of-ppm, depending on the purification method. These increases are associated with the preferential dissociation of hydrogen-containing species. Investigations of the structural, thermal, and mechanical properties of the glass were compared as a function of purification method, and the influence of impurity content on these material attributes is presented.     

Glass Formation and Crystallization Behavior of a Novel GeS2–Sb2S3–PbS Chalcogenide Glass System

In the present work, a large glass-forming region was found in the novel GeS₂–Sb₂S₃–PbS system, in which up to 58 at.% PbS could be incorporated without deteriorating the thermal and physical properties of glasses. Infrared (IR) transmitting glass ceramics with a large amount of small-sized crystals (<100 nm) were then produced by choosing sub-stable compositions and annealing at fairly low temperatures (15°–30°C above T _g) for long durations (up to 100 h). Crystals were identified by X-ray diffraction as Pb₂GeS₄, PbGeS₃, PbS, PbSb₂S₄, etc., depending on base glass compositions. Compared with base glasses, glass ceramics showed much improved thermal shock resistance and fracture toughness, making them good candidate materials for IR optics.     

Formation of Bi2ZnB2O7 Nanocrystals in ZnO–Bi2O3–B2O3 Glass Induced by Femtosecond Laser

We report on the formation of Bi₂ZnB₂O₇ crystal structures with designated patterns in ZnO–Bi₂O₃–B₂O₃ glass by femtosecond laser direct writing. The crystallization mechanism in glass is investigated by crystallization kinetics analysis and simulation of the three‐dimensional temperature field distribution. The crystallized regions show larger third‐order optical nonlinearity than the unirradiated region in glass by Z‐scan technique. This finding is of great potential in application of nonlinear optical integrated devices and development of new nonlinear materials.     

Enhanced Up‐Conversion Luminescence in Er3+‐Doped 25GeS2·35Ga2S3·40CsCl Chalcogenide Glass–Ceramics

Enhanced luminescence in rare‐earth‐doped chalcogenide glass–ceramics is of great interest for the potential integrated optoelectronic devices. However, fundamental mechanism on the enhancement of luminescence upon crystallization remains largely unknown. We report the fabrication and characterization of wide transmission chalcogenide glass and glass–ceramics based on the 25GeS₂·35Ga₂S₃·40CsCl:0.3Er glass composition, and discuss the mechanism of enhanced luminescence. By monitoring the ⁴I_9/2–⁴I_15/2 of Er³⁺ transition, up‐conversion luminescence of 12 times higher was observed in glass–ceramics compared with that in base glass. Electron paramagnetic resonance (EPR) and Raman scattering spectroscopies were employed to obtain the information of selective environment of Er³⁺ ions and microstructural evolution with the crystallization progress. Both of them evidenced that the enhanced up‐conversion luminescence was mainly related to the local environmental evolution from a mixed chlorine‐sulfur coordination to a low phonon energy chlorine coordination in the residual glassy matrix of glass–ceramics.     

A Study on Crystallization Kinetics of Thermoelectric Bi2Se3 Crystals in Ge–Se–Bi Chalcogenide Glasses by Differential Scanning Calorimeter

Novel glass‐ceramics with embedded thermoelectric Bi₂Se₃ crystals were prepared from glass matrices in the Ge₂₀Se_100?xBi_x (x = 5, 10, 12 mol%) system. Based on DSC results performed at different heating rates, characteristic activation energies (E_c) and Avrami exponents (n) were obtained and analyzed by using Kissinger's relation, Ozawa's method, Augis–Bennett approximation and Matusita–Sakka theory. XRD results showed that pure Bi₂Se₃ crystalline phase precipitated upon annealing at different temperatures for various time. The crystal size and crystalline fraction in the samples could be tuned by controlling the annealing time.     

Phase Evolution of SiO2–Al2O3–ZnO–CaO–ZrO2–TiO2‐Based Glass with Added Y‐PSZ Particles

Yttria partially stabilized zirconia Y‐PSZ/glass‐ceramic composites were prepared by reaction sintering using powder mixtures of a SiO₂–Al₂O₃–ZnO–CaO–ZrO₂–TiO₂‐based glass and yttria partially stabilized zirconia (Y‐PSZ). The glass crystallized during sintering at temperatures of 1173, 1273, and 1373 K to give a glass‐ceramic matrix for high‐temperature protecting coatings. With the increasing firing time, the added zirconia reacted with the base glass and a glass‐ceramic material with dispersed zircon particles was prepared in situ. Furthermore, the added zirconia changed the crystallization behavior of the base glass, affecting the shape, amount, and distribution of zircon in the microstructure. The bipyramid‐like zircon grains with imbedded residual zirconia particles turned out to have two growth mechanisms: the inward growth and the outward growth, and its rapid growth was mainly dominated by the later one. For comparison, the referenced glass‐ceramic was prepared by sintering using exclusive glass granules and its crystallization behavior at 1173–1373 K was examined as well. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were used to characterize the crystallization behavior of the base glass and the phase evolution of the Y‐PSZ/glass‐ceramic composites.     

Thermodynamic Modeling of the HfO2–La2O3–Al2O3 System

Based on phase equilibria, thermodynamic, and crystal structure data, the thermodynamic modeling of HfO₂–La₂O₃–Al₂O₃ system is presented. Liquid phase is described by the modified quasichemical model considering the short‐range ordering in liquid solution. Solid solutions are described by the ionic sublattice model considering respective crystal structure. The model (La³⁺, Hf⁴⁺)₂(Hf⁴⁺, La³⁺)₂(O^2?, Va)₆(O^2?)₁(Va, O^2?)₁ successfully describes the structure defect, homogeneity range, and thermodynamic property of pyrochlore solid solution. A set of optimized model parameters is obtained which reproduces most experimental data well. Isothermal sections, liquidus and solidus projections, and Scheil reaction scheme are constructed.     

Microwave Processing for Improved Ionic Conductivity in Li2O–Al2O3–TiO2–P2O5 Glass‐Ceramics

Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) was synthesized using a glass‐ceramics approach through crystallization in a conventional box furnace and a modified microwave furnace. The microstructure of samples that were microwave processed at 1000°C showed a larger average grain size (0.87 μm) when compared with the grain size of conventionally processed samples (0.30 μm) at the same temperature. Microwave processing led to significant enhancement of the conductivity when compared with conventional processing for all crystallization temperatures investigated. The highest total conductivity achieved was of glass microwave processed at 1000°C, with a conductivity of 5.33 × 10^?4 S/cm. This conductivity was five times higher than that of LATP crystallized conventionally at the same temperature.     

Crystallization Kinetics and Dielectric Properties of a Low‐Fire CaO–Al2O3–SiO2 Glass + Alumina System

The crystallization kinetics and dielectric properties of a low‐dielectric, low‐temperature, cofirable ceramic system comprised of CaO–Al₂O₃–SiO₂ (CAS) glass and alumina have been investigated. Crystalline phases including pseudowollastonite (CaSiO₃), anorthite (CaAl₂Si₂O₈) and cristobalite (SiO₂) are formed during firing the pure CAS glass. The crystallization kinetics of both pseudowollastonite and cristobalite exhibit Avrami‐like behavior, and the results show apparent activation energies close to that of diffusion of alkali ions in the glass. With added alumina content greater than a critical value, the above crystalline phases are completely suppressed but more anorthite is formed. This result is attributed to the rapid dissolution kinetics of alumina into the CAS glass. As the degree of crystallization increases with firing time, the dielectric loss of the composite decreases significantly, however, with dielectric constant remaining relatively unchanged.     

Er2O3 Doping Effect on Varistor Properties and Multiimpulse Stress Behavior of ZnO–PrO1.83–CoO–Cr2O3–Dy2O3 Ceramics

The Er₂O₃ doping effects on varistor properties and impulse aging behavior of the ZnO–PrO_1.83–CoO–Cr₂O₃–Dy₂O₃ ceramics were investigated in the range of 0–2.0 mol%. The nonlinear coefficient increased from 42 to 56 with an increase in the amount of Er₂O₃. The clamp voltage ratio (K) decreased with an increase in the amount of Er₂O₃. The varistors doped with 2.0 mol% in the amount of Er₂O₃ exhibited the best clamping characteristics, with K = 1.43–1.83 at an impulse current of 1–50 A. The varistors doped with 0.25 mol% in the amount of Er₂O₃ exhibited the strongest electrical stability, with the variation rate of the breakdown field of ?0.5%, the variation rate of the nonlinear coefficient of ?5.5%, and the variation rate of the leakage current of ?1.5% after applying 400 times at an impulse current of 400 A     

Glass Formation in the PbO–GeO 2 System

The glass-forming region in the PbO–GeO2 system is studied. To increase the glass-forming limit in this system, the tempering rate of the samples has to be increased using special methodological practices. The dependence of the temperature of the synthesis of lead germanate glass on the PbO content is obtained. It is shown that the corrosion of alumina crucibles proceeded during the synthesis of lead germanate glass. The dependence of the thickness of the corroded layer of the alumina crucible wall on the time of the synthesis of the glass of the 55PbO · 45GeO2 composition, mol % at 900°С is obtained. It is proved that the obtained glass is X-ray amorphous within the whole range of compositions in the PbO–GeO2 system.     

Thermal and optical properties of La2O3–Ga2O3– (Nb2O5 or Ta2O5) ternary glasses

La₂O₃–Ga₂O₃–M₂O₅ (M = Nb or Ta) ternary glasses were fabricated using an aerodynamic levitation technique, and their glass‐forming regions and thermal and optical properties were investigated. Incorporation of adequate amounts of Nb₂O₅ and Ta₂O₅ drastically improved the thermal stabilities of the glasses against crystallization. Optical transmittance measurements revealed that all the glasses were transparent over a wide wavelength range from the ultraviolet to the mid‐infrared. The refractive indices of the glasses increased and the Abbe number decreased upon substituting Ga₂O₃ with Nb₂O₅, and the decrease in the Abbe number was significantly suppressed when Ta₂O₅ was incorporated into the glass. As a result, excellent compatibility between high refractive index and lower wavelength dispersion was realized in La₂O₃–Ga₂O₃–Ta₂O₅ glasses. Analysis based on the single‐oscillator Drude–Voigt model provided more systematical information and revealed that this compatibility was due to an increase in the electron density of the glass.     

Influence of Microwave‐Assisted Pechini Method on La0.80Sr0.20Ga0.83Mg0.17O3–δ Ionic Conductivity

With the aim of investigating the microwave influence on the electrolyte material properties, La_0.80Sr_0.20Ga_0.83Mg_0.17O_2.815 was prepared by both a conventional and a microwave‐assisted sol–gel Pechini method. With respect to the conventional Pechini method (hereafter SGP), the microwave assisted process (hereafter MWA‐SGP) guaranteed a faster procedure, reducing the time needed to remove the excess solvents to complete the polyesterification reaction from some days to a few hours. In fact, when a MWA‐SGP method was used, powders having higher phase purity were obtained. The sintering process at 1,450 °C of the powders prepared by both methods yielded pellets with similar density values (≥92% of theoretical). Nevertheless, only by microwave‐assisted process single‐phase products were obtained and no secondary phases such as tetragonal LaSrGaO₄ and LaSrGa₃O₇ were detected. These by‐products have been demonstrated to be detrimental for conductivity. Indeed, pellets obtained by MWA‐SGP method showed oxygen ionic conductivity values higher (about 30–40%) than those checked for SGP samples, thus demonstrating the important role of the microwave process on reducing time and costs and on improving the electrolyte properties.     

Formation Behavior and High Electrical Conductivity of Metastable Lithium Iron Silicate Crystals in Rapid Quenching of Li2O–Fe2O3–SiO2 Melts

The formation behavior of spinel‐type LiFeSiO₄ crystals in the quenching of melts in the Li₂O–Fe₂O₃–SiO₂ system was examined. It was found that high quenching rates of 10³ ~ 10⁶ K/min are favorable for the formation of LiFeSiO₄ crystals. The rapid quenched samples showed high electrical conductivities of the order of 10^?2–10^?4 S/cm at room temperature and low activation energy for conduction of 0.1–0.2 eV. Both valences of Fe²⁺ and Fe³⁺ were present in the melt‐quenched samples, and rapid‐quenched samples showed ferrimagnetism. It is proposed that the chemical composition of LiFeSiO₄ formed in the rapid quenching of melts would be spinel‐type Li_1 + xFe³⁺_1 ? xFe²⁺_xSiO₄. Because the Li_1 + xFe³⁺_1 ? xFe²⁺_xSiO₄ crystalline phases are metastable, the rapid quenching technique is necessary for their synthesis. The effects of quenching rate and composition on the formation of spinel‐type LiFeSiO₄ and on the electrical conductivity of quenched samples were discussed.     

Conduction Mechanisms in BaTiO3–Bi(Zn1/2Ti1/2)O3 Ceramics

Polycrystalline BaTiO₃–Bi(Zn_1/2Ti_1/2)O₃ (BT–BZT) ceramics have superior dielectric properties for high‐temperature and high‐energy density applications as compared to the existing materials. While it has been shown that the addition of BZT to BT leads to an improvement in resistivity by two orders of magnitude, in this study impedance spectroscopy is used to demonstrate a novel change in conduction mechanism. While nominally undoped BT exhibits extrinsic‐like p‐type conduction, it is reported that BT–BZT ceramics exhibit intrinsic n‐type conduction using atmosphere‐dependent conductivity measurements. Annealing studies and Seebeck measurements were performed and confirmed this result. For BT, resistivity values were higher for samples annealed in nitrogen as compared to oxygen, whereas the opposite responses were observed for BZT‐containing solid solutions. This suggests a fundamental change in the defect equilibrium conditions upon the addition of BZT to the solid solution that lowered the carrier concentration and changed the sign of the majority charge carrier. This is then also linked to the observed improvement in resistivity in BT–BZT ceramics as compared to undoped BT.