Phases In Glass-ceramics Research Articles

Impact of Structural Motifs on the Ionic Diffusion Mechanism in Sulfide-Based Solid Electrolytes

Sulfide-based solid electrolytes, such as lithium thiophosphate (LPS) with compositions (Li2S) 𝑥 (P2S5)1− 𝑥 and lithium Germanium thiophosphate (LGPS [Li10GeP2S12]), exhibit high ionic conductivity, rendering them promising for solid-state batteries (SSBs). However, their practical application is limited due to their low electrochemical stability and grain boundary resistance. To overcome these challenges, we explore the formation of glass-ceramic phases within the lithium thiophosphate family. Our investigation centers on the mechanism of ionic diffusion in LPS (with three compositions) and LGPS (with two distinct crystal systems) in their crystalline and glass-ceramic phases. Employing ab initio molecular dynamics (AIMD) simulations, we identify and classify the structural motifs responsible for the diffusion of Li-ions. Notably, Li2P2S6 (x = 0.5) exhibits a high activation energy for diffusion, while Li7P3S11 (x = 0.7) demonstrates elevated Li-ion diffusivity in its crystalline phase. Interestingly, the transport properties do not vary with compositions suggesting that the ion mobility is independent of the underlying structural motifs present in the glass-ceramic phases of LPS. Our structural similarity analysis also reveals a similar Li environment in the glass-ceramic phase, regardless of LPS compositions. Furthermore, increasing the crystallinity in glass-ceramic Li7P3S11 increases the amount of P2S7 4- motifs, and its percolation changes the Li environment creating a conduction pathway for Li-ion diffusion. In the case of LGPS, disorder within the glass-ceramic phase significantly diminishes ion transport similar to the behavior observed in LPS. However, the tetragonal and triclinic crystal structures reveal distinct ionic diffusion mechanisms in terms of conduction pathways. Our study emphasizes the importance of structural motifs to devise the optimal strategy for designing solid electrolyte materials. Figure 1

The effect of ZrO2 on the structure, properties and crystallization behavior of transparent lithium disilicate based glass-ceramics

The effects of ZrO2 on the parent glass network structure, crystallization behavior, and properties of lithium aluminosilicate glass-ceramics by various amounts of ZrO2 were investigated. The main crystalline phases of transparent glass-ceramics are quartz solid solution and Li2Si2O5. The increase of ZrO2 addition promotes an increasing of Q3(Zr) tetrahedral proportion in the glass network, resulting a reduction of ZrO2 nucleus. The increase of ZrO2 content also effectively improves the fracture toughness of glass-ceramics, but reduces the transmittance significantly. In this work, the glass with the 1 mol% ZrO2 nucleated at 545 °C for 2 h and crystallized at 800 °C for 2h possesses the excellent comprehensive properties, which exhibited the Vickers hardness of 6.91 GPa, the fracture toughness of ∼1.40 MPa·m1/2, and the transmittance at 550 nm of 90 %. It provides significant potential applications in the display protective cover.

Flash sintering glass–ceramic treatment of Sr-contaminated soil waste

Effective disposal of radioactive waste is crucial for safe development of nuclear energy. In this study, flash sintering technology is used for the first time to quickly solidify simulated Sr-contaminated soil waste. The waste can be converted into a glass–ceramic phase by heating the waste at 1100 °C for 1 min during flash sintering. The phase evolution during flash sintering as a function of density and amorphous fraction was systematically investigated. Additionally, the microstructural evolution of the matrices and the leaching behavior of simulated waste elements (e.g., Sr) were evaluated. This study explores the feasibility of using flash sintering for treating radioactive contamination waste.

Effect of ZnO/Li2O ratio on the structure and properties of Li2O-ZnO-SiO2-P2O5 glass-ceramics sealants

In order to meet the sealing temperature of copper alloy below 1000 °C, a kind of Li2O-ZnO-SiO2-P2O5-(B2O3+Al2O3+K2O) (LZS) glass-ceramics with high expansion coefficient and high resistivity was synthesized via the melting method and then crystallized through controlled cooling. The network structure, thermal properties, crystal phase transition, thermal expansion coefficient, and high-temperature resistivity have been investigated. As the mass ratio of ZnO/Li2O increases, the network structure of the LZS glass is strengthened, leading to an increase in the glass transition and crystallization temperature. Moreover, the predominant crystal phases in LZS glass-ceramics transit from Li2SiO3 to Zn[Zn0.1Li0.6Si0.3]SiO4 and subsequently to Zn2SiO4. At a ZnO/Li2O ratio of 3, a cristobalite phase with a high expansion coefficient emerges. The change in crystal phase results in a variation in the coefficient of thermal expansion (CTE) of glass-ceramics, ranging from 13.2 to 11.2 × 10−6 K−1. At a ZnO/Li2O ratio of 3, the softening temperature of glass-ceramics is minimized. Moreover, as the ZnO/Li2O mass ratio increases, the resistance of crystallized glass decreases first and then increases. The maximum resistivity is achieved at a ZnO/Li2O mass ratio of 5. By optimizing the mass ratio of ZnO/Li2O, it is determined that when the mass ratio of ZnO/Li2O is 3, the CTE is 12.4 × 10−6 K−1, and the softening temperature (Ts) is 679.8 °C, which is the best material for sealing applications.

Advancing the prediction of crystalline phases in glass-ceramics via machine learning

Lithium aluminosilicate (LAS) glass-ceramics are widely utilized in diverse application, owing to their outstanding properties such as high transparency, high fracture toughness and ultra-low thermal expansion. The development of LAS glass-ceramics has traditionally relied on the phase diagram to identify primary crystalline phases. However, this approach is limited by constrained composition ranges and unknown heating treatment parameters, hindering the efficient development of high-performance glass-ceramics. In this study, we establish a comprehensive small-scale database of LAS glass-ceramics, comprising 751 samples characterized by 27 compositions, nucleation temperature, nucleation time, crystallization temperature, crystallization time and 13 crystalline phases. We employ five algorithms, i.e. Random Forest (RF), eXtreme Gradient Boosting (XGBoost), Classification and Regression Trees (CART), K-Nearest Neighbors (K-NN) and Multi-Layer Perceptron (MLP) Classifier to predict the potential crystalline phases. Our results demonstrate that RF achieves the best overall performance, with the highest accuracy of 0.8609, the lowest hamming loss of 0.0142, and the highest micro F1 score of 0.9234. This work advances the understanding and prediction of crystalline phases in LAS glass-ceramics, providing valuable insights for the development and optimization of these materials.

Impact of adding Na2SiF6 on the crystal phase and copper valence state in glass ceramics made from leftover granite for use as architectural ornamentation

Abstract The accumulation of granite waste can result in the occupation of a considerable amount of land resources. Using granite waste as glass ceramics for architectural decoration represents a potential solution to this issue. The microstructure, valence state, and crystalline phase of copper ions were examined by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The findings demonstrated that the concentration of Na2SiF6 affects the valence condition of Cu ions in crystallized glass. The crystalline phases of the sample containing 1.84 wt% Na2SiF6 consisted of forsterite (MgSiO3) and diopside (CaMgSi2O6), and the Cu+ accounted for 39.9% of the total Cu ions in the sample which showed a grey-black color. For the sample containing 3.67 wt% Na2SiF6, the crystalline phases consisted of richterite (Na, F) syn (Na (Na, Ca) Mg5Si8O22F2), cuprite (Cu2O), and forsterite, its Cu+ accounted for 39.9%, and the sample appeared orange-red. With the increase of Na2SiF6 content, the percentage of Cu+ in the total Cu ions showed an increasing trend, and the corresponding red color of the samples gradually deepened.

Large dielectric properties of niobate-titanate glass ceramics prepared by powder sintering method

Niobate-titanate glass-ceramics with large dielectric constant were prepared by the dual optimization strategy employed——glass powder sintering method and simultaneous introduction of multiple nucleating agents. The study delved into the crystallization and microstructure of the glass ceramics, with a subsequent characterization of their dielectric and ferroelectric properties. In this investigation, the crystalline phase underwent a transformation from the Pb2Nb2O7 phase of G700 glass ceramics to the coexistence of (Pb, Sr)TiO3 and (Ba, Sr, Pb)Nb2O6 phase of G1100 glass ceramics. The crystal phase content exhibited a notable increase from 29 % to 82 %. The relative density of the glass ceramics reached a high of 99.4 %. The maximum dielectric constant recorded was 1493, accompanied by a maximum energy efficiency of up to 88.0 %. These results underscore the potential of glass ceramics as a promising material for Multilayer Ceramic Capacitor (MLCC) dielectric layers.

High-alumina and low-lithium glass-ceramics modulated by heat treatment and its structural evolution mechanism

In this work, one high-alumina and low-lithium glass-ceramic was successfully developed. The crystal phase, structure and properties of glass-ceramics were precisely modulated by heat treatment. DSC, XRD, TEM and SEM were used to investigate crystallization behavior and the results show that a high alumina content can refine crystal particles. Additionally, FTIR, SAXS NMR and XPS were used to investigate the effect of heat treatment on structure and its modulation mechanism was systematically analyzed. The findings indicate that crystallinity is positively correlated with the glass network polymerization degree. Moreover, the properties of product were evaluated using Vickers hardness and transmittance tests, revealing that the mechanical properties of glass-ceramics could be improved while maintaining transmittance with appropriate heat treatment. Ultimately, this method of heat treatment to modulate glass-ceramics properties provides valuable guidance for high-performance glass-ceramics development.

Production of glass-ceramics from fluorinated sludge: Structure, properties and leaching risk

Fluorinated sludge (FS) is a solid waste with massive discharge. To mitigate environmental pollution and optimize resource utilization, FS was employed in the fabrication of glass-ceramics. The impacts of different FS additions (40–60 wt%) and sintering temperatures (1000–1150°C) on the crystalline phase, microstructure, properties and leaching performance of glass-ceramics were discussed. Crystallization kinetics were studied to analyze the crystallization mechanism of glass-ceramics. The results showed that the predominant crystalline phases of glass-ceramics were anorthite and fluorite. The increasing sintering temperature facilitated the growth of crystals and the polymerization of glass network, resulting in improved densification. When the FS addition was 50%, sample sintered at 1100°C with a flexural strength of 47 MPa exhibited the best comprehensive performance: a density of 2.29 g/cm3, Vickers hardness of 584 HV. FS addition has resulted in an increase in the activation energy of glass-ceramic. The main pattern of crystallization was volume crystallization in glass-ceramic. The F− leaching concentration of all glass-ceramics is lower than 1 mg/L, which will not cause environmental pollution. Only when the FS addition was above 55%, there was a leaching risk for Cu and Zn in the sample due to its poor acid resistance. It is a promising way for FS to manufacture glass ceramics as a high-value construction material.

Effects of CaO/SiO2 ratio and CaCl2 content on the densification, microstructure, and properties of sintered CaO–MgO–Al2O3–SiO2–CaCl2 glass-ceramic

The effects of CaO/SiO2 ratio (basicity) and CaCl2 addition amount on the properties of CaO–MgO–Al2O3–SiO2–CaCl2 glass-ceramics (GC) were investigated. When sintered at 825 °C, the increase in basicity from 0.35 to 0.75 reduced the porosity of GCs from 1.1 to 0.8 vol%, but the increase of CaCl2 addition amount from 5 to 10 wt% increased the porosity from 0.8 to 7.0 vol%. The main crystalline phase of GC changed from augite (Ca(Mg0·7Al0.3) (Si1·7Al0.3)O6) to Ca10Al12Cl2Si5O37 by increasing the CaCl2 addition amount to 7.5 wt%. The increase in CaCl2 addition had adverse effects on the bending strength and Vickers hardness, while the rise in basicity deteriorated the bending strength but had little impact on the Vickers hardness. This study may have a guiding significance for preparing slag-based GCs and treating CaCl2-containing wastes.

Optimized growth of LiZnBO3 monoclinic phase in lithium zinc borate glass ceramics for electrode material

Glass-ceramics (GCs) of glass composition 20ZnO.30Li2O.50B2O3 were prepared via controlled heat treatment at hold times of 2h, 4h, 6h and 8h at crystallization peak temperature (846K). The effect of the hold time of heat treatment on the physical, structural, optical, and electrochemical properties was studied. XRD study revealed the formation of a pure LiZnBO3 crystalline phase. FTIR study revealed the transformation of BO4 units to BO3 units with an increase in the time of heat treatment. Optical band gap energy has been estimated from Diffuse Reflectance spectroscopy and, its values range from 3.26eV–3.36eV. Electrochemical properties were studied using Cyclic Voltammetry and compared with parent glass composition. The GC 20ZnO.30Li2O.50B2O3 heat treated for 8h exhibits the highest value of specific capacitance (∼48 mAh/gV) and energy density (∼18 J/g) indicating that it can be used as an electrode material in Li-ion batteries.

Effect of thermal poling in sodium tantalum phosphate glass-ceramics

Eu3+-doped sodium tantalum phosphate glass-ceramics containing bronze -like perovskite crystalline phase Na2Ta8O21 were obtained with different crystalline states (degree of crystallinity and average crystallite size) by a suitable control of the heat-treatment time and temperature of the precursor glass. Luminescence properties of Eu3+ in these materials are in agreement with a progressive insertion of the rare earth ions in the sodium tantalate Na2Ta8O21 phase, as probed by a clear decrease of the intensity ratio between transitions [5D0 →] 7F2/7F1 and narrowing of characteristic emission bands. Thermal poling insights were performed on these glassy and glass-ceramic materials and the experimental conditions had to be carefully optimized in the glass-ceramics to avoid electrical sparks and sample break associated with dielectric breakdown of the samples. Suitable and stable thermal poling treatments could be performed at 250 °C and 900 V under N2 atmosphere on both glass and glass-ceramics. These first insights pointed out a lower migration kinetic of sodium ions when compared to the precursor glass as well as a lower content of depleted ions, since part of sodium is supposed to be “frozen” inside the crystalline phase in glass-ceramics. Despite these lower kinetic poling conditions, a poled sodium depleted layer whose thickness depends on the poling time was successfully formed at the anode side. Reflectance infrared spectroscopy was also used to investigate the structural changes in the poled layer. These IR data pointed out that structural changes induced by thermal poling are mainly promoted in the phosphate network rather than tantalate units in both glass and glass-ceramics in agreement with a selective sodium migration from the remaining glassy phase. Macroscopic induced SHG measured by the Maker fringes technique is also consistent with the EFISH model and quantitative simulations of these data allowed to estimate second order nonlinear optical susceptibilities χ(2) ten to twenty times lower in the glass-ceramics than in the precursor glass. Such electric behavior is discussed in terms of dielectric properties of heterogeneous materials and interfacial polarization mechanisms between crystallites and glassy phase.

Preparation and characterization of MgO-Al2O3-SiO2 glass-ceramics with different MgO/Al2O3 ratio and La2O3 addition

MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by traditional melting and sintering method, and the effects of MgO/Al2O3 ratios and La2O3 contents on the microstructure and physicochemical properties of MAS glass-ceramics were studied. Herein, differential scanning calorimetry (DSC), X-ray diffraction (XRD), fourier-transform infrared spectrophotometer (FTIR), Field-emission scanning electron microscopy (FESEM), density, corrosion resistance, dielectric properties and thermal expansion coefficient (CTE) were carried out to evaluate the properties of both parent glass and glass-ceramics samples. The results show that adjusting the MgO/Al2O3 ratio from 0.69 to 0.47 can increase the characteristic temperatures of transition temperature (Tg) and crystallization peak temperature (Tp) in MAS parent glass. The reduction of MgO/Al2O3 ratio could promotes the precipitation of α-cordierite phase (Mg2Al4Si5O18), and the grain size of α-cordierite phase were increased from 200 to 500 nm. When the MgO/Al2O3 ratio was 0.63, the MA-2 sample has the highest flexural strength of 127.46 MPa. Furthermore, we also investigated the influence of La2O3 addition on the structure and properties of MAS glass-ceramics by employed MA-2 sample as a reference. The results show both the Tg (742–748 °C) and Tp (936–943 °C) of parent glass exhibit a slightly increasing with the La2O3 content was increased from 0.0 to 2.0 wt%. The La2O3 addition show a negligible influence on the crystal phase and morphology of MAS glass-ceramics. With increasing of the La2O3 content, the MAS glass-ceramics samples have a larger density (2.58–2.76 g/cm3) and a better chemical stability, and the CTE (6.12–8.17 × 10−6/°C), εr (5.04–6.17), and the flexural strength (127.46–150.15 MPa) also show an increased change trends. The prepared MAS glass-ceramics can be packaged with high expansion coefficient chips (such as GaAs) and is expected to become a potential candidate of dielectric materials for electronic devices, especially for high frequency applications in integrated circuits.

Monitoring decomposition of Eu3+ doped LaPO4 nanocrystals in glass using Eu3+ as an optical probe for applications in temperature sensing

The methods to directly introduce crystals of known chemistry, size, and optical properties into a glass matrix are useful to circumvent some limitations related to the control of the growth of crystalline phases in glass-ceramics. The emission spectrum of LaPO4:Eu3+ is characteristic for highly symmetrical coordination of Eu3+ and very distinct from the emission spectrum of Eu3+ in amorphous host, which allows for its application as an optical probe. Here, Eu3+ - doped LaPO4 crystals were prepared using solid state reaction and added into various phosphate glass melt before quenching. From the changes in the micro-luminescence spectra, the decomposition occurs along with the diffusion of the Eu3+ ions into the glass confirming that the measurement of the micro-luminescence allows one to precisely track the crystal's decomposition inside the composite. It is demonstrated, for the first time to our knowledge, that the thermometric sensitivity of the Eu3+ ions can be enhanced by adding the LaPO4:Eu3+ crystals into phosphate fluoride glasses due to special separation of the crystallites during the composite preparation and also to the reduction of the self-absorption of the 5D1→7F1 emission. The composite material is promising for applications in temperature sensing.

Study on glass-ceramic prepared by zinc leaching residue and solidification mechanism of heavy metals

Zinc leaching residue is a hazardous solid waste with difficult treatment, high hazard and high yield, and it is a great challenge to treat it efficiently, harmlessly and economically among the various methods available. This paper introduced a micro-crystallization method to process zinc leaching residue into glass-ceramics with excellent performance and high value. The heavy metals in the raw material were well solidified in the glass-ceramics, eliminating the high hazard of heavy metals and other components. The bending strength, compressive strength, and Vickers hardness of the glass-ceramics prepared at the sintering temperature of 950 °C were 69.2 MPa, 434.3 MPa, and 6.66 GPa, respectively, while the water absorption, density, and acid and alkali corrosion resistance were excellent. The relationship between the microstructure and properties of glass-ceramics was investigated using traditional analytical techniques such as XRD, Raman, and SEM, and the mechanism of solidification of heavy metals Pb, Zn and Mn in glass ceramics were innovatively researched by the modified BCR sequential leaching test and XPS analysis. Anorthite and diopside ferrian were the two main crystalline phases in glass-ceramics. The sintering temperature affected the formation and growth of crystals, and determined the crystal size and crystallization rate, thus affecting the properties of glass-ceramics. Part of the heavy metal was solidified in the amorphous phase in the glass-ceramic, and the other major part entered the crystal as an impurity substitution to form a solid solution at a specific location. The zinc leaching residue based glass-ceramic had been studied, which was pioneering and with excellent performance and environmental safety. Thus, the safe and economical treatment of these hazardous wastes promotes the clean, green and efficient development of related industries.

Crystallization behavior, thermal and fluorescence properties of germanate glass ceramic based on Ga2O3 replacing GeO2

This paper focuses on the effects of Ga2O3/GeO2 ratios and heat treatment on the structure, crystallization and fluorescence properties of Gd2O3-Ga2O3-GeO2-Nd2O3 glass system. According to the results, the glass network's structural stability suffers when the ratio of Ga2O3/GeO2 is low. As the ratio of Ga2O3/GeO2 continues to increase, Ga3+ ions are transformed into [GaO4] to participate in the construction of the glass network structure. The principal phase of glass-ceramics is GdGaGe2O7, and the secondary phase is Ga4GeO8, GeO2 and Gd3Ga5O12. Moreover, the glasses with high content of Ga2O3 is easier to prepare translucent glass-ceramics with uniform grain distribution and size. The emission spectrum intensity of glass-ceramics is obviously improved compared with that of glasses. In addition, it is found that the emission peak of Nd3+ ions generated by 4F3/2 → 4I11/2 electron transition is stably redshifted from 1060 nm to 1088 nm by microcrystallization, which means a small range of spectrum is adjustable.

Phase Transformations upon Formation of Transparent Lithium Alumosilicate Glass-Ceramics Nucleated by Yttrium Niobates

Phase transformations in the lithium aluminosilicate glass nucleated by a mixture of yttrium and niobium oxides and doped with cobalt ions were studied for the development of multifunctional transparent glass-ceramics. Initial glass and glass-ceramics obtained by isothermal heat-treatments at 700–900 °C contain YNbO4 nanocrystals with the distorted tetragonal structure. In samples heated at 1000 °C and above, the monoclinic features are observed. High-temperature X-ray diffraction technique clarifies the mechanism of the monoclinic yttrium orthoniobate formation, which occurs not upon high-temperature heat-treatments above 900 °C but at cooling the glass-ceramics after such heat-treatments, when YNbO4 nanocrystals with tetragonal structure undergo the second-order transformation at ~550 °C. Lithium aluminosilicate solid solutions (ss) with β-quartz structure are the main crystalline phase of glass-ceramics prepared in the temperature range of 800–1000 °C. These structural transformations are confirmed by Raman spectroscopy and illustrated by SEM study. The absorption spectrum of the material changes only with crystallization of the β-quartz ss due to entering the Co2+ ions into this phase mainly in octahedral coordination, substituting for Li+ ions. At the crystallization temperature of 1000 °C, the Co2+ coordination in the β-quartz solid solutions changes to tetrahedral one. Transparent glass-ceramics have a thermal expansion coefficient of about 10 × 10−7 K−1.

Effects of TiO2 content and crystallization treatments on elastic modulus of alkali-free aluminosilicate glass

In this work, we focused on studying the effects of TiO2 content and crystallization treatment on the elastic modulus of alkali-free aluminosilicate glass in the CaO–MgO–Al2O3–SiO2 (CMAS) system. Five groups of alkali-free CMAS parent glass with different TiO2 (0.30–1.50 wt%) components were designed, and several kinds of measurements including of Fourier-transform infrared spectrophotometer (FTIR), differential scanning calorimetry (DSC), x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and elastic modulus tests were carried out to evaluate the performance of both parent glass and glass-ceramics samples. The results show the elastic modulus of alkali-free parent glass decreased gradually with the TiO2 content increased from 0.30 to 1.50 wt%, the maximum value of elastic modulus was 91.62 ± 0.80 GPa for T-1# sample (0.30 wt% TiO2) and it decreased to 77.99 ± 1.73 GPa for T-5# sample (1.50 wt% TiO2). The crystallization kinetics analysis of both T-1# and T-5# parent glass indicate the parent glass is in favor to surface crystallization. After the heat treatment at 1000–1150 °C for crystallization, the major crystal phase of both T-1# and T-5# group glass-ceramics was found to be anorthite (CaAl2Si2O8), with the crystal sizes around 200–500 nm. However, the crystallization treatments have shown different influence on the elastic modulus of T-1# and T-5# parent glass. The elastic modulus value of T-1# group glass-ceramics gradually decreased from 91.62 ± 0.80 GPa to 80.22 ± 2.84–90.82 ± 4.27 GPa after crystalized at 1000–1150 °C. On the contrary, the elastic modulus value of T-5# group glass-ceramics increased from 77.99 ± 1.73 GPa to 80.50 ± 4.57–88.91 ± 6.44 GPa after crystalized at 1000–1150 °C. This results further confirmed that the elastic modulus values of glass-ceramics main depends on the parent glass and the crystal phase in glass-ceramics.

Synthesis, structure and properties of Na4GeS4

The Na2S-Na4GeS4 section of the binary system Na2S-GeS2 has been studied and the crystal structure of the Na4GeS4 compound was determined from single-crystal X-Ray diffraction data. The physical properties of Na4GeS4 were characterized by X-ray powder diffraction, TG/DTA, SEM-EDX, Raman spectroscopy and electrochemical impedance spectroscopy. Na4GeS4 crystallizes with a new type of structure in the non-centro-symmetric space group Im, a = 10.9822(9) Å, b = 29.652(2) Å, c = 20.0391(16) Å, β = 105.77(1) (°), V = 6279.96(90) Å3 and Z = 30. The Na4GeS4 asymmetric unit that contains 76 atoms is made up of 10 isolated GeS4 tetrahedra. The 31 sodium atoms are located between these tetrahedra. The distorted NaS6 octahedra, NaS5 trigonal bipyramids, NaS5 square pyramids and NaS4 tetrahedra share corners, edges or faces. The electrical conductivity [2.7 × 10−5 S cm−1 (Ea = 0.41 eV) at 25 °C] of the Na4GeS4 glass phase, prepared by mechanochemical synthesis, is two orders of magnitude higher than that of the glass-ceramic phase, prepared by the combination of mechanochemical and solid-state synthesizes [9.8 × 10−8 (Ea = 0.65 eV) at 25 °C].

Crystallization kinetics, structural and mechanical properties of transparent lithium aluminosilicate glass-ceramics

Transparent glass-ceramic in the SiO2-Li2O-Na2O-Al2O3-BaO-P2O5-ZrO2 system were prepared by the three-stage heat treatment process. The effects of Al2O3 content on the crystallization behavior, microstructure, and physical properties of the glass-ceramics were investigated by differential scanning calorimeter (DSC), X-Ray Diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscope (SEM). As the Al2O3 increases from 4 to 7 mol%, all the Al3+ ions are present in the [AlO4] tetrahedra and participate in the glass network, resulting in the more compact structure of glass. The increasing in the glass network connectivity leads to the higher crystallization activation energy, hindering the formation of lithium disilicate and promoting the precipitation of Al-containing crystalline phases. The main crystalline phase of glass-ceramics transform from lithium disilicate and petalite to LixAlxSi1-xO2, and the transmittance of glass-ceramics decrease. Upon the three-steps heat treatments of 540°C/4h + 610°C/2h + 730°C/4h, the glass-ceramic with 4 mol% Al2O3 containing petalite and lithium disilicate crystals shows high transparency of ∼85% in the visible light range, high hardness 8.07 GPa, and fracture toughness of 1.37 MPa·m1/2, which shows great potential in the applications of protective material for mobile devices.