Li Al Si Research Articles

Radiative properties of ‘Eu’in Li–Al–Si–O ceramics: Effect of ‘Si’ to ‘Li’ ratio

Four Li–Al–Si– O -based ceramic compounds with varying Si to Li ratios were synthesized via a high-temperature reaction route and characterized by X-Ray diffraction, scanning electron microscopy, and photoluminescence techniques. Eu was used as an activator in these four compositions namely, LiAlSiO 4 , LiAlSi 2 O 6 , LiAlSi 3 O 8 , and LiAlSi 4 O 10 , and the radiative properties were evaluated. The activator concentration was optimized in all these samples to 2 mol%. The photoluminescence emission intensity and decay time values increased with the Si to Li ratio. The relative intensities of the emission spectra and the lifetime values indicated that the rare earth ion stabilizes itself at interstitial positions in the lattice having approximately C 2v symmetry. The chromaticity indices for the four ceramic samples doped with Eu were calculated that showed near red emission for all. To get an idea about their commercial utility, color purity, quantum efficiencies for the phosphors were evaluated. The emission profile of the prepared samples was compared with a commercial sample. The Judd-Ofelt parameters, transition probabilities, branching ratios, and quantum efficiencies were also calculated for these systems. It was observed that the metal-ligand bond covalency decreased with an increase in the Si to Li ratio which was responsible for the increase in the emission intensities and luminescence decay time values.

Ionic conduction mechanism of a lithium superionic argyrodite in the Li–Al–Si–S–O system

Unique interstitial Li+ and O2−/S2− site disorder lower the percolation threshold for 3D Li-ion diffusion in lithium argyrodite Li6.15Al0.15Si1.35S6−xOx (LASSO).

Thermal expansion coefficient tailoring of LAS glass-ceramic for anodic bondable low temperature co-fired ceramic application

The Li–Al–Si glass-ceramics were prepared by conventional glass-ceramic fabrication method. The influences of Na2O content on the sintering property, microstructure, and coefficient of thermal expansion were investigated. The results show that the coefficient of thermal expansion of LAS glass-ceramics can be tailored to match that of silicon by the addition of Na2O content. Na2O has a remarkable influence on the crystallinity of Li–Al–Si glass-ceramic. The coefficient of thermal expansion of Li–Al–Si glass-ceramic is thus tunable between that of glass phase and crystal phase. The Si–O bond length change in stretch vibration modes introduced by Na2O also contributes to the variation of coefficient of thermal expansion of the Li–Al–Si glass-ceramics. The coefficient of thermal expansion of the Li–Al–Si glass-ceramic with 1.5 wt% Na2O addition is about +3.34 ppm/°C at 350 °C and shows a good compatibility to that of silicon in a wide temperature range, which makes it a promising candidate for anodic bondable low temperature co-fired ceramic substrate applications.

Enhanced thermal and mechanical properties of Li–Al–Si composites with K2O–B2O3–SiO2 glass for LTCC application

Abstract In this study, Li–Al–Si composites with K2O–B2O3–SiO2 (KBS) glass were synthesized by traditional solid-state method, and the phase composition, microstructure, sintering behavior as well as properties were systematically investigated. The specimen with 4 wt % Al2O3 sintered at 1020 °C exhibited a high thermal conductivity of 10.46 W/(mK) and a flexural strength of 180.23 MPa. The sintering temperature was reduced from 1020 °C to 900 °C using KBS glass frits as sintering additives. The sample with 2.0 wt % KBS, sintered at 900 °C for 2 h, possessed a relatively high thermal conductivity of 9.83 W/(mK), a high flexural strength of 215.09 MPa, and a low dielectric constant of 6.24, thus demonstrating its potential for LTCC application.

Superionic lithium conductor with a cubic argyrodite-type structure in the Li–Al–Si–S system

All-solid-state lithium batteries have been proposed as solutions to safety issues associated with conventional lithium batteries; consequently, their development is important. To that end, we conducted a material search of solid electrolytes in the Li4+xAlxSi1−xS4 system. High-temperature (HT) and low-temperature (LT) modifications of novel argyrodite-structured phases were obtained at around x = 0.1 by melt quenching. The HT-argyrodite phase showed the highest ionic conductivity (2.5 × 10−4 S cm−1) at 28 °C, with an activation energy of 40 kJ mol−1; this conductivity value is three orders of magnitude higher than those of Li4+xAlxSi1−xS4 solid solutions. The relationship between ionic conductivity and phase-type was elucidated. An all-solid-state lithium battery using an HT-argyrodite-phase electrolyte exhibited a discharge capacity of over 120 mAh g−1 and an excellent discharge efficiency of about 100% after the second cycle, demonstrating that this material is suitable for use in practical all-solid-state batteries.

Synthesis and electrochemical performance of rod-like spinel LiMn2O4 coated by Li–Al–Si–O solid electrolyte

Li1.05Co0.1Mn1.9O3.95F0.05 rods with a spinel structure were synthesized by a topochemical conversion route, and a Li–Al–Si–O (LASO) glassy solid electrolyte was used to modify the surface of the cathode material. The structure and electrochemical properties were investigated using X-ray diffraction, scanning electron microscope, transmission electron microscope and electrochemical tests. XRD, SEM and TEM observations show that Li1.05Co0.1Mn1.9O3.95F0.05 materials have a single crystal of cubic spinel structure and exhibit a rod-like morphology with a diameter of 400–500 nm. The electrochemical results indicate that LASO-coated Li1.05Co0.1Mn1.9O3.95F0.05 rods exhibit an excellent rate capability and cycle stability at elevated temperatures and high rates. The initial discharge capacity of the LCMOF-rod-LASO sample is 93.9 mA h g−1 under 10 C at 55 °C, and the capacity retention ratio is higher than 96% after 200 cycles. Even under 15 C at 55 °C, the cathode material shows a high capacity of 87 mA h g−1. The cyclic voltammograms and impedance spectra results reveal that the LASO coating enhances the kinetics of the lithium-ion diffusion through the surface layer and the charge transfer reaction, improving the electrochemical activity of the cathode. Thus, the LASO-coated Li1.05Co0.1Mn1.9O3.95F0.05 rods have shown potential for high power applications in lithium ion batteries.

Solid-state synthesis and heat capacity measurements of ceramic compounds LiAlSiO4, LiAlSi2O6, LiAlSi3O8, and LiAlSi4O10

Number of lithium-based oxide ceramics in Li–Al–Si–O system were synthesized by solid-state reaction route using Li2CO3, Al2O3, and SiO2. The progress of the reaction was monitored using thermogravimetry. A model-free approach was employed to fit the temperature versus mass loss data. Heat capacities were measured as a function of temperature using differential scanning calorimetry. Variation of lithium/silicon ratio resulted in change in heat capacity and average crystallite size in each compound.

High lithium ion conductive Li 7La 3Zr 2O 12 by inclusion of both Al and Si

High lithium-ion (Li +) conductive garnet-structured lanthanum lithium zirconate (LLZ) solid electrolyte is prepared by incorporation of appropriate amounts of silicon (Si) and aluminum (Al). The resultant pelletized LLZ obtains total Li + conductivity of 6.8 × 10 − 4 S cm − 1 at 298 K. This improved conductivity is nearly identical with the bulk Li + conductivity of the LLZ reported earlier, suggesting that the grain boundary resistance is effectively reduced by the incorporation of Si and Al. Microanalyses by transmission electron microscopy coupled with energy-dispersive X-ray microanalysis and electron energy-loss spectroscopy revealed the presence of amorphous Li–Al–Si–O with nano crystalline LiAlSiO 4 at grain boundaries. Fast lithium-ion transport around the amorphous Li–Al–Si–O/LiAlSiO 4 interface will facilitate Li + transport between the LLZ particles, resulting in the improvement of the total Li + conductivity of LLZ.

Phase Stabilities, Electronic and Electrochemical Properties of Compounds in the Li—Al—Si System.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Vacuum heat treatment of LiAlO 2 densified silicon nitride ceramics

The aim of the present work has been to produce high-dense Si 3N 4 ceramics by a cheaper pressureless sintering method and then to attain vacuum heat treatment to remove residual grain boundary glass in gaseous form. LiAlO 2 was used as a sintering additive rather than using Li 2O, since its grain boundary glass is not stable above 1200 °C. LiAlO 2 was synthesised from 42% Li 2CO 3 and 58% Al 2O 3 powder mix reacting together at 1450 °C for 3 h in a muffle furnace. X-ray analysis showed that 95% LiAlO 2 was obtained. LiAlO 2 was milled and added to silicon nitride powder as a sintering additive. Hot-pressing and pressureless sintering of LiAlO 2 containing Si 3N 4 compacts were carried out at temperatures between 1450–1750 °C. The sintered samples were vacuum heat-treated at elevated temperatures under high vacuum to remove intergranular glass and to increase refractoriness of Si 3N 4 ceramics. Scanning electron microscope images and weight loss results showed that Li in grain boundary glass (Li–Al–Si–O–N) was successfully volatilised, and oxidation resistance of the sintered samples was increased.

Compositional and structural variations in the ternary system Li – Al – Si

Abstract The Li–Al–Si ternary system has been investigated and four ternary phases characterized using both powder and single crystal X-ray diffraction data. LiAlSi and Li7Al3Si4 crystallize in the F4̅3m, cubic system, Li18Al2Si6 in tetragonal I41/amd and Li15Al3Si6 in hexagonal P63/m space group. The structure of LiAlSi (a = 5.94 Å), previously reported from powder data, has been confirmed. The new compound Li7Al3Si4 has been identified and, due to a higher lithium content, its cell parameter is slightly larger (a = 6.115 Å). The tetragonal cell (a = 6.179(1) Å, c = 12.199(4) Å) of Li18Al2Si6 may be considered as a (1 × 1 × 2) supercell of the cubic one. Structural variations are strongly correlated to compositional fluctuations and atomic substitutions, in every case the SI–Al network displays some covalent character. In the Li15Al3Si6 hexagonal cell, bonding is more covalent leading to a heterographite-like SI–Al network.

Preparation and characterization of a powder precursor, consisting of oxides of Li–Al–Si in the form of hydroxyhydrogel for synthesis of β-spodumene ceramics

Powder precursors of different compositions in the system Li 2O–Al 2O 3–SiO 2 were prepared in the hydroxy-hydrogel form by wet interaction technique in aqueous medium for ultimate synthesis of low expansion ceramics. Properly processed powder precursors were characterized. It was found that the powder precursor produced by this process was in meta-stable state with the aluminium in the tetrahedral as well as in the octahedral co-ordination sites. The confirmation of this finding was made by IR analysis of the prepared powder precursors as well as the heat treated samples. It was further found that the complete dehydroxylation did not occur even after heat treatment at 700 °C. The XRD analysis of the samples, when heat treated at 700 °C confirmed the detection of β-spodumene phase and the formation of this phase was almost complete when the samples were heat treated at 1000 °C.