Li2O Al2O3 SiO2 System Research Articles

TRANSPARENT GLASS-CERAMICS BASED ON LITHIUM ALUMINOSILICATE SYSTEM

Methods of laser micro- and nanomodification structure of transparent dielectrics open promising prospects for the creation of a new type glass-crystalline materials and new applications. In this work, after a brief excursion into the history of glass-ceramics, transparent aluminosilicate glass-ceramics are discussed, mainly using the example of the Li2O–Al2O3–SiO2 system, and the areas of their new applications. The recently discovered possibilities of laser micromodification of structures and direct laser writing of elements photonics and integrated optics in their volume are considered. In this case, special attention is paid to transparent glass-ceramics with coefficient of thermal expansion close to zero.

Effect of substitution of ZrO2 by SnO2 on crystallization and properties of environment-friendly Li2O–Al2O3–SiO2 system (LAS) glass-ceramics

In this study, a transparent and environmentally friendly Li2O–Al2O3–SiO2 (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO2 by SnO2 on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO2–SnO2 increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO2–SnO2 was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa.

Transparent glass–ceramics with (Eu3+,Yb3+):YNbO4 nanocrystals: Crystallization, structure, optical spectroscopy and cooperative upconversion

In the present work, we report on a comprehensive study of crystallization, structure and optical spectroscopy of transparent glass–ceramics with (Eu3+,Yb3+):YNbO4 nanocrystals synthesized by secondary heat-treatments of glass of the Li2O–Al2O3–SiO2 system, for the first time, to the best of our knowledge. Heat treatments result in volume crystallization of RENbO4 with the sizes of 4–15nm. Crystals of rare-earth niobates with disordered fluorite structure (T′) appear during heat-treatment at 720–740°C for 6h, crystals with tetragonal structure (T) appear at higher temperatures or longer durations of heat-treatment, and in samples heat-treated at 1000°C, the monoclinic form (M) is detected additionally. Rare-earth niobates act as nucleating agents for bulk crystallization of β-quartz solid solutions, the main crystalline phase of the glass–ceramics, which ensures their good thermo-mechanical properties. Optical spectroscopy confirms entering of both Eu3+ and Yb3+ ions into the RENbO4 nanophase and their specroscopic properties variation according to the T′→T→M phase transformations. Under UV excitation, glass–ceramics heat-treated at 900°C provide intense red emission with the color coordinates x=0.665, y=0.335 (CIE 1931). In the sample, heat-treated at 1000°C, a partial reduction of Eu3+ to Eu2+ is observed which allows for tuning the color properties of emission. When excited in the near-IR by an InGaAs diode, the initial glass and glass–ceramics show red cooperative upconversion due to the 2Yb3+→Eu3+ energy transfer. The efficiency of the latter is ~10%. The developed materials due to the good emission and thermo-mechanical properties are promising for the development of color-tunable red phosphors.

Effect of CaO content on structure and properties of low temperature co-fired glass–ceramic in the Li2O–Al2O3–SiO2 system

Glass–ceramics based on the Li2O–Al2O3–SiO2 system were synthesized by the conventional melt-quenching technology. The glass–ceramics were designed based on silicon oxide replacement with simultaneous increasing calcium oxide. The effects of CaO on the microstructure, densification, thermal, dielectric and mechanical properties of the glass–ceramics were investigated. This glass–ceramic has a low softening point and could be sintered at a low temperature of 800 °C. The addition of CaO promotes the formation of the CaMgSi2O6 phase and could improve the microstructure, densification and mechanical property. The coefficient of thermal expansion of the glass–ceramic increases with the content of CaO and could match that of silicon chips. The sample LAS2 (2.1 wt% CaO) sintered at 800 °C for 0.5 h exhibits excellent properties: high density of 2.48 g/cm3, low dielectric constant of 6.8 and loss of 3.7 × 10−3, high three point bending strength of 154 MPa, and low CTE value of 1.9 × 10−6/°C.

The Role of GeO 2 and In 2 O 3 in the Glass-Ceramic Formation and Microstructure of Lithium Alumino-Silicate Glasses

The crystallization characteristics of the glasses based on the Li2O–Al2O3–SiO2 system have been investigated. The base glass composition was modified by partial replacement of GeO2 for SiO2 and In2O3 for Al2O3. The effect of the compositional variation on the crystallization products of the glasses and the type of the solid solution (ss) phases formed as well as the resulting microstructure were traced by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). A decrease in the endothermic and exothermic temperatures was detected by the replacement processes. β -spodumene ss, β -eucryptite ss, lithium meta- and di-silicate, lithium aluminum germanate and two forms of indium-containing phases (LiInSi2O6 & In2Si2O7 phases) were mostly developed in the crystallized glasses. The objective of the present work is to understand the role of the glass oxide constituents in determining the type of the crystalline phases formed, their solid solution formed and the microstructure of the resultant glass-ceramic materials.

Crystallisation and characterisation of dielectric glass ceramics in Li2O–Al2O3–SiO2 system

Glass ceramics in the Li2O–Al2O3–SiO2 system have been synthesised to produce bulk materials grown in a glass phase via quenching followed by controlled crystallisation. The crystallisation and microstructure of Li2O–Al2O3–SiO2 (LAS) glass–ceramic with nucleating agents (B2O3 and/or P2O5) are investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopy and the effects of B2O3 and P2O5 on the crystallisation of LAS glass are also analysed. The introduction of both B2O3 and P2O5 promotes the crystallisation of LAS glass by decreasing the crystallisation temperature and adjusting the crystallisation kinetic parameters, allows a direct formation of β spodumene phase and as a result, increases the crystallinity of the LAS glass ceramic. Microstructural observations show that the randomly oriented, nanometre sized crystalline is found with residual glass concentrated at crystallite boundaries. Furthermore, it is interesting that codoping of B2O3 and P2O5 creates not much effect on the crystallisation temperature. The dielectric properties of the glass–ceramics formed through controlled crystallisation have a strong dependence on the phases that are developed during heat treatment. The dielectric constant is continuously increased and the dielectric loss is decreased with addition of additives where mobile alkali metal ions (e.g. Li+) are incorporated in a crystal phase and minimise the residual glass phase.

Crystallisation behaviour and in vitro characterisation of TiO2 doped spodumene glass ceramics

Crystallisation behaviour of Li2O–Al2O3–SiO2 system (LAS) glass ceramics containing TiO2 doping and non-doping is investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The introduction of TiO2 decreases the crystallising peak temperature Tp and the crystallising activation energy E and improves the crystallisation stage to obtain fine crystal with a size of ∼100 nm. A controlled surface reaction of the ceramic is an important factor governing the bioinert and biodegradation nature of the implanted ceramic. The addition of TiO2 improves the chemical durability of the glass ceramic, by reducing the number of non-bridging oxygens, suppressing the tendency for amorphous phase separation and provides a more dense and stable structure. This results in a decrease in the release rate of Li+, Al3+ and Si4+ ions in a simulated body fluid.

Crystallization behavior during cooling and glass-forming ability of Al2O3-poor Li2O–Al2O3–SiO2 melts

The influence of K2O/(MgO+K2O) on some melt properties, including crystallization during cooling of melts and glass-forming ability, was investigated in the Li2O–Al2O3–SiO2 system with low Al2O3 content. The dependence of viscosity on K2O/(MgO+K2O) above 1000°C showed a monotonic decrease due to the reduction of [MgO4] concentration and the conductivity also decreased due to the larger ion radius of K. The temperature dependence of conductivity for all melts showed an abrupt change at one temperature due to crystallization in which temperature of crystallization decreases with increase of K2O. The crystallization behavior near liquidus temperature was studied quantitatively by calculating the crystal volume fraction from apparent viscosity value. The glass-forming ability of the melts was discussed by using data related with viscosity and crystallization. Finally, it was suggested that the melts with K2O/(MgO+K2O)⩾0.75 have a good glass-forming ability.

Transparent Nd3+-Activated Glass-Ceramics in the Li2O–Al2O3–SiO2System: Physicochemical Aspects of Their Preparation and Optical Characteristics

The spectral–optical properties of transparent neodymium-activated lithium aluminosilicate glass-ceramics with titanium dioxide as a crystallization catalyst are investigated. The compositions of the initial glasses and the temperature–time schedules of heat treatment that provide a way of preparing highly homogeneous samples with low optical losses are determined. The most important parameters characterizing emission from the 4F3/2metastable state of neodymium ions are obtained by analyzing the optical spectra of rare-earth ions in terms of the Judd–Ofelt theory. It is shown that the introduction of phosphorus oxide into the composition of glass-ceramics leads to a considerable increase in the stimulated emission cross section for the basic 4F3/2–4I11/2transition, even though the rare-earth activator is not incorporated into the crystalline phase. It is found that acceptable quantum yields of fluorescence with the retention of a high heat resistance of glass-ceramics can be achieved by decreasing the volume fraction of the crystalline phase. The lasing testing of the materials prepared is performed in a setup with a lamp pumping. The low lasing parameters can be associated with the specific features in the optical properties of glass-ceramics, primarily, with the revealed depolarization of polarized light due to the presence of microstresses at interfaces.

Nucleation efficiency in lithia-alumina-silica glasses

The efficiency of TiO2 as a nucleating agent in the Li2O—Al2O3—SiO2 system is explored over a wide composition range. Sharp changes in crystal growth rate, which strongly influence nucleation rate, are observed near the Li2O·Al2O3—SiO2 composition line and are ascribed to changes in fluidity of the glass at the crystal growth front caused by rejection of lithia-rich material by the growing crystals. A mechanism for triggered nucleation at the growth front is advanced to explain a discrepancy between crystal growth rate and final particle size. The general implications of the results are briefly discussed.