System Li2O Research Articles

Effect of impurities and disordering on the photoluminescence of crystals and glasses in the system Li2O - 7GeO2

The work is devoted to the study of photoluminescence spectra of weakly polar ferroelectric crystals Li2Ge7O15 and Li2O – 7GeO2 glasses. For all initial samples was observed the wide intensive luminescence band with maximum in the region of 525–550 nm. The spectral distribution of intensity and the position of the maximum of the band for a Li2Ge7O15 crystal depended on the excitation wavelength (λex=405 nm or 365nm were used). The spectral profile of the luminescence band was broadened in glass containing of 0.67% copper. The intensity of the luminescence band was decreased 6 times for glass doped with Cr3+ ions (0.01%) as compared with glass containing Cu2+ ions. The intense luminescence band of Cr3+ ions with λmax=659nm was appeared starting from 600. The assumption about the nature of the broad luminescence band observed in both nominally pure and doped glasses and crystals was made: the source of luminescence can be germanium - oxygen complexes [GeO4] and [GeO6] of the tetrahedral and octahedral configuration in the material structure.

Growth of bulk β-BaB2O4 crystals from solution in LiF-Li2O melt and study of phase equilibria

The authors employ methods of spontaneous crystallization on a platinum loop, modified visual polythermal analysis (VPA), solid phase synthesis, differential thermal analysis (DTA), X-ray powder diffraction (XRD) analysis and chemical analyses, in order to study chemical processes and phase formation in the BaB2O4–LiF–Li2O system. In this system the fields of primary crystallization of β-BaB2O4 are determined. The primary crystallization field of the low-temperature barium borate phase for the BaB2O4–LiF–Li2O system is proved to lie in the range 72–60 mol% BaB2O4. A series of experiments have been carried out on the growth of bulk barium borate crystals in this system.

Physical-Chemical Properties of Low-Melting Phosphate Glasses in Relation to Tin Oxide Content

The influence of SnO on the physicochemical properties of low-melting glasses in the system Li2O–SnO–P2O5(LSP), intended for use in compositions for vacuum-tight low-temperature bonding of different materials, was studied. The low values of Tg promoted high spreadability of LSP-glass powders at temperatures below 450°C (typical for gluing electronic articles). The mass losses upon boiling of LSP-glasses varied over a wide range (0.19 – 4.55%), and in terms of chemical resistance the glasses characterized by mass losses below about 3% surpass the lead-borate glasses widely used in solders. The values of nv for LSP-glasses were raised to values characteristic for lead-borate glasses by optimizing the alkali-content ratio.

Structural investigation of hydrous phosphate glasses

Dissolved water has major impact on the physical and chemical properties of phosphate glasses. In the present study we have investigated the structural response to water incorporation for glasses in the system Li2O–MgO–Al2O3–P2O5. Glasses containing 0–8 wt% H2O were synthesised at 500 MPa confining pressure in internally heated gas pressure vessels at 1323 K (LMP, Al-poor glass) and 1423 K (LMAP, Al-enriched glass). Water contents of glasses were determined by pyrolysis and subsequent Karl-Fischer titration (KFT) and/or by infrared spectroscopy. Density varies nonlinearly with water content implying large structural changes when adding up to 2 wt% H2O to the dry glass. Glass Transition temperatures measured by differential thermal analysis (DTA) continuously decrease with water content. The trend can be explained by depolymerisation of the phosphate network. Near-infrared spectroscopy shows that even in Al poor glasses only a minority of dissolved water is present as H2O molecules, but the largest amount is present as OH Groups formed by hydrolysis of P–O–P bonds. The network is stabilised by aluminium which is predominantly six-coordinated in these glasses as shown by 27Al MAS NMR spectroscopy. With increase of Al in the glasses, breaking up of the Phosphate network through hydrolysis is depressed, i.e. much lower OH Contents are formed at same total water content. Network depolymerisation upon addition of H2O is evident also from 31P MAS NMR spectroscopy. While Phosphate tetraheda are crosslinked by two to three bridging oxygen in dry glasses, diphosphate Groups are dominant in glasses containing 8 wt% H2O.

Effect of cooling modes on defect structure in Cu-doped LiTaO3

In this work we have study the defects structure of non-stoichiometric solid solutions of Cu-doped LiTaO3, the changes of Curie temperature with rate of % Cu2+ (mol) in rapid and slow cooling modes, allows us to analyze the defect structure of solid solutions synthesized in ternary system Li2O–Ta2O5–(CuO)2 in vicinity of LiTaO3. A simple comparison between our theoretical results and the experimental data of Tc shows that there is a cooling mode effect on the structural properties of Cu-doped LiTaO3. Consequently, our proposed models are able to describe the defect structure of Cu-doped lithium tantalate.

Optical properties and structure particularities of LiNbO3 crystals grown from a boron-doped melt

A series of LiNbO3:B crystals was grown from the melt doped by boron. It is shown that LiNbO3:B crystals possess an increased resistance to optical damage. We have found changes according to Raman spectra confirming the ordering of Li+, Nb5+ cations and vacancies along the polar axis. The chemical interactions were studied in the system Li2O–B2O3–Nb2O5. Boron cations are unable to incorporate into a cation sublattice of LiNbO3, but they change the physic-chemical structure of a melt. It contributes to an increased structure and optical uniformity of LiNbO3:B.

КОМБІНАЦІЙНЕ РОЗСІЮВАННЯ СВІТЛА У СКЛОПОДІБНОМУ Li2B4O7

Lithium tetraborate is a promising material to be used in the production of solid electrolytes and solid-state batteries. A powerful tool for investigating its structure in the B2O3–Li2O system is Raman spectroscopy. The Raman spectra were investigated using the XploRA PLUS (HORIBA Jobin Yvon) Raman spectrometer at the temperature of T = 300 K within the 70–2000 cm–1 range. The excitation wavelength was 785 nm, the spectral resolution was no worse than 1 cm–1. As a result of the study, we have determined the nature of vibrational modes. We detected a fine structure in the 70–400 cm–1 range, which we found to correspond to normal vibration of the lithium-oxygen structural complexes in the structure of [LiO6] frames, and also vibrations and librations of [LiO6] frame and the BO3 and BO4 groups in the structure of [B4O7]2– cluster as a whole. In the 400–800 cm–1 range the superposition of vibrations of [LiO4] clusters and [BO4] tetrahedrons takes place, whereas their normal vibrations are detected in the 800–1354 cm–1 range. In the 1300–2000 cm–1 range we observed the manifestation of two-phonon states, the normal vibrations of borate rings, and the symmetric stretching of the BO3 flat triangles, and detected two peaks that have not been observed previously. The obtained results show that the Raman spectra of glassy Li2B4O7 generally display a single-mode behavior and are caused by a combination of vibrations of different types which are interconnected via the frame structure of the glass consisting of complex boron-oxygen and lithium-oxygen structural complexes.

Effects of Oxide Ions on the Electrodeposition Process of Silicon in Molten Fluorides

We studied the effects of O2− ions on the coordination structure of Si ions and the electrodeposition process of Si films in molten fluorides using SiO2 powder (as a source of Si) and Li2O (as a source of O2−). High-temperature Raman spectroscopic data revealed that the dissolution of SiO2 in molten KF, LiF-KF, and LiF-NaF-KF without Li2O was proceeded by the formation of silicate ions, with the [Si2O5]2− ion acting as the dominant species. On the other hand, when 3.0 mol% Li2O was added to molten LiF-KF and LiF-NaF-KF, the intensity of Raman band due to [SiO3F]3− ion was increased compared to that without Li2O system, which indicated that the O2− ions could cause breakage of Si-O-Si bonds of SiO2 or [Si2O5]2− ions. Furthermore, the reduction currents, attributed to the reduction of Si ions, increased significantly by the addition of Li2O; moreover, the thickness and current efficiency of the electrodeposited polycrystalline Si layer prepared by potentiostatic electrolysis was improved. These results indicated that the O2− ions can change the coordination structure of Si ions in molten fluorides and that the design of the molten salts bath is a key technology for fabricating high-quality Si layers with high current efficiency.

Low-Temperature Co-Firing Ceramic Li2Zn3Ti4O12 Modified by Li2O–ZnO–B2O3 Eutectic Additive

Amaterial sintering at temperature 950°C for the technology of low-temperature co-firing ceramic used in the production of electronic components was developed in the system Li2O–ZnO–TiO2. The effect and method of synthesizing the eutectic sintering additive content in the system Li2O–ZnO–B2O3 on the compaction process and the dielectric properties of the obtained material were studied. The developed ceramic is characterized by the permittivity e = 17.7 and dielectric Q-factor 407 MHz.

Analysis of Correlation between Density Variations and Defect Structure of W6+ : LiTaO3

We investigate the defect structure of non-stoichiometric solid solutions of WO3-doped LiTaO3 in correlation with the evolution of the density within our theoretical approach. The dopant concentration and the mechanism of substitution, which depends of the ionic rays of different cations that exit into the network, have an effect on crystalline parameters and, consequently, on the density. In order to explain the defect structure of solid solutions synthesized in the ternary system Li2O–Ta2O5–(WO3)2 in a vicinity of LiTaO3,, we have shown a convergence between theoretical and experimental results by the application of our theoretical approach combined with the new proposed vacancy models. We conclude that the new vacancy models are able to describe the defect structure and the substitution mechanism in each solid solutions of WO3-doped lithium tantalate.

Solubility of Li2O in an LiCl–KCl Melt

The phase diagrams of the binary LiCl–Li2O system and the quasi-binary [LiCl–KCl]–Li2O systems containing 10 and 20 mol % KCl have been built using thermal analysis of cooling curves and isothermal saturation curves. The solubility of Li2O in LiCl–KCl melts is determined in the temperature range 500–800°C. The solubility of Li2O in the melts LiCl, LiCl–KCl (10 mol %) and LiCl–KCl (20 mol %) decreases as the KCl content increases;at 650°C, it is 11.5, 7.7, and 3.9 mol %, respectively.

Properties of the LiCl-KCl-Li2O system as operating medium for pyro-chemical reprocessing of spent nuclear fuel

Crystallization temperatures (liquidus and solidus) in the LiCl-Li2O and (LiCl-KCl)-Li2O systems with the KCl content of 10 and 20 mol.% were obtained with independent methods of thermal analysis using cooling curves, isothermal saturation, and differential scanning calorimetry. The linear sweep voltammetry was applied to control the time of the equilibrium establishment in the molten system after the Li2O addition, which depended on the composition of the base melt and the concentration of Li2O. The fragments of the binary LiCl-Li2O and quazi-binary [LiCl-KCl(10 mol.%)]-Li2O and [LiCl-KCl(20 mol.%)]-Li2O phase diagrams in the Li2O concentration range from 0 to 12 mol.% were obtained. The KCl presence in the LiCl-KCl-Li2O molten mixture in the amount of 10 and 20 mol.% reduces the liquidus temperature by 30 and 80°, respectively, but the region of the homogeneous molten state of the system is considerably narrowed, which complicates its practical application. The Li2O solubility in the molten LiCl, LiCl-KCl(10 mol.%) and LiCl-KCl(20 mol.%) decreases with increasing the KCl content and is equal to 11.5, 7.7 and 3.9 mol.% at 650°С, respectively. The LiCl-KCl melt with 10 mol.% KCl can be recommended for practical use as a medium for the SNF pyro-chemical reprocessing at temperature below 700 °C.

First high-pressure synthesis of rossmanitic tourmaline and evidence for the incorporation of Li at the X site

Lithium is an important component of some tourmalines, especially in chemically evolved granites and pegmatites. All attempts at synthesizing Li-rich tourmaline have so far been unsuccessful. Here we describe the first synthesis of rossmanitic tourmaline at 4 GPa and 700 °C in the system Li2O–Al2O3–SiO2–B2O3–H2O (LASBH) from seed-free solid starting materials consisting of a homogenous mixture of Li2O, γ-Al2O3, quartz and H3BO3. The solid run products after 12-day run duration comprise rossmanitic tourmaline (68 wt%), dumortierite (28 wt%) and traces of spodumene (3 wt%) and coesite (1 wt%). Tourmaline forms idiomorphic, large prismatic crystals (30 × 100 μm), which are inclusion free and chemically unzoned. The refined cell dimensions of the tourmaline are: a = 15.7396(9) A, c = 7.0575(5) A, V = 1514.1(2) A3. Conventionally, the Li+ ion is assumed to exclusively occupy the octahedral Y site in the tourmaline structure to a maximum of 2 Li per formula unit (pfu). However, the chemical composition of our synthetic tourmaline determined by electron microprobe and secondary ion mass spectroscopy results in the formula: X(☐0.67(11)Li0.33(11))Y(Al2.53(10)Li0.47(10))Z(Al6)T(Si5.42(15)B0.58(15))O 18 B (BO3) 3 V+W [(OH)2.40(3)O1.60(3)], wherein a significant amount of Li occupies the X site for charge balance requirements. Reliable assignment of the OH-stretching vibrations in a polarized single-crystal Raman spectrum such as a single-crystal XRD structure refinement, confirms the incorporation of Li at the X site [0.24(9) and 0.15(5) XLi pfu, respectively]. The SREF data show that the Li–O1 distances are shortened significantly in order to compensate for the smaller ionic radius of Li+ compared to Na+, K+ or Ca2+ at the X site, i.e., Li is closer to the Si6O18 ring and to a sevenfold coordination with oxygen.

Experimental and theoretical study of the density of Cu-doped LiTaO3

In this work, we have investigated experimentally and theoretically, the evolution of a density of solid solutions synthetised in the vicinity of LiTaO3 in the ternary system Li2O–Ta2O5–(CuO)2 with a rate of % Cu and by two modes of cooling (slow and rapid cooling), for different solid solutions synthetised. We have realized that the mechanisms of non-stoichiometry for different phases at Cu2+ are sensitive to the cooling modes. In order to study by our theoretical approach, the correlation of the evolutions of density with defects structure of Cu-doped LiTaO3, we have proposed vacancy models that can explain the mechanism of substitution. The correlation of the density evolution with defects structure of Cu-doped LiTaO3, is investigated by using the theoretical approach which combined with proposed vacancy models in order to explain the substitution mechanism. The analytical modeling reproduce experimental measurements specifying the nature of substitution required.

Copper-Vapor Laser Induced Local Crystallization of Glasses in the System Li2O–B2O3–GeO2

Experiments on local modification of lithium-borogermanate (LBG) glass with the composition (molar fraction, %) 25Li2 O ∙ 25B2O3 ∙ 50GeO by copper-vapor laser radiation on the main lasing lines (510.6 and 578.2 nm) in the visible range and on the sum frequency in the UV range (271 nm) are described. Local surface crystallization of LBG glass by a laser beam with 2 – 15 μm crystals precipitated by means of laser heating of the sample at temperature somewhat below t g is demonstrated for the first time. X-ray phase analysis and confocal RS spectroscopy show that the polar phase LiBGeO4 is the only phase formed as a result of crystallization. Crystallization obtains with UV- and visible-range radiation.

Glass structure and crystallization of Al and B containing glasses belonging to the Li2O–SiO2system

The aim of the present work is to investigate the effect of substituting B2O3for Al2O3in a non-stoichiometric lithium disilicate (Li2Si2O5, LS2) glass composition belonging to the system Li2O–K2O–Al2O3–SiO2.

Li2Ca2Si2O7: Structural, spectroscopic and computational studies on a sorosilicate

Synthesis experiments in the system Li2O–CaO–SiO2 resulted in the formation of single-crystals of Li2Ca2Si2O7. Structural investigations were based on single-crystal diffraction. At ambient conditions the compound has the following basic crystallographic data: hexagonal symmetry, space group P6122, a=5.0961(2)Å, c=41.264(2)Å, V=928.07(6)Å3, Z=6. Structure solution was performed using direct methods. The final least-squares refinement calculations converged at a residual of R(|F|)=0.0260. From a structural point the lithium calcium silicate belongs to the group of pyrosilicates containing [Si2O7]-groups. Additional lithium and calcium cations are incorporated between the silicate dimers and are coordinated by four and six nearest oxygen neighbours, respectively. Each [LiO4]-tetrahedron shares two common corners with directly neighboring tetrahedra forming zweier single-chains which are running parallel to 〈100〉 in z-levels defined by the presence of the 61[001]-screw axes. From the corner-sharing [LiO4]- and [SiO4]-moieties a three dimensional framework can be constructed. An interesting feature of this framework is the presence of an O[3]-type bridging oxygen linking three tetrahedra (one [LiO4]- and two [SiO4]-units). Structural similarities with other silicates are discussed in detail. The high-temperature behavior of the Si–O, Ca–O and Li–O bond distances in Li2Ca2Si2O7 was investigated by in-situ single-crystal X-ray diffraction in the range between 65 and 700°C. From the evolution of the lattice parameters, the thermal expansion tensor αij has been determined. The structural characterization has been supplemented by micro-Raman spectroscopy. Interpretation of the spectroscopic data including the allocation of the bands to certain vibrational species has been aided by DFT-calculations.

Role of manganese on the structure, crystallization and sintering of non-stoichiometric lithium disilicate glasses

The structural role of Mn was investigated in a relatively simple non-stoichiometric lithium disilicate (Li2Si2O5) based glass composition. Glasses were prepared by partially replacing SiO2 by MnO2 from the base glass belonging to the system Li2O–K2O–Al2O3–SiO2. An overall depolymerization of the glass network was observed according to magic angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared (FTIR) spectroscopic studies, suggesting a network modifier role for Mn. However, thermal analysis, phase segregation and nucleation in the glasses suggested that Mn might also act as network former. Moreover, calculated crystal field parameters from UV-Visible spectroscopy, showing high ligand field strength (Δo) and Racah inter electronic repulsion (B) indicate the possible existence of Mn as individual molecular entities in the interstitials of the glass network. This paper discusses the implications of this structural role of Mn on the crystallization of bulk glasses and on the sintering behaviour and crystallization of glass powder compacts.

Preparation and characterization of TeO2–WO3–Li2O glasses

Glasses in the TeO2–WO3–Li2O system were prepared by using conventional melt-quenching technique. Glass formation range of the system and thermal, physical and structural features of the ternary glasses were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and FTIR analysis according to the equimolar substitution of TeO2 by WO3+Li2O and increasing Li2O content at constant TeO2. Thermal behavior of the glasses was studied in terms of glass transition temperature (Tg), crystallization temperature (Tc/Tp) and glass stability against crystallization (∆T). Density (ρ), molar volume (VM), oxygen molar volume (VO), oxygen packing density (OPD), average cross-link density (n—c), Poisson's ratio (μcal) and number of bonds per unit volume (nb) values were calculated for the physical investigation of the glasses. FTIR spectra of the glasses were interpreted in terms of the structural transformations on the glass network by the changing composition.

Mixed-Alkali Effect in Li2O–Na2O–K2O–B2O3 Glasses: Infrared and Optical Absorption Studies

The mixed-alkali effect (MAE) has been investigated in the glass system (40 − x)Li2O–xNa2O–10K2O–50B2O3 (0 mol% ≤ x ≤ 40 mol%) through density, modulated differential scanning calorimetry (DSC), and optical absorption studies. From the absorption studies, the values of the optical band gap (E opt) for direct transition and Urbach energy (ΔE) have been evaluated. The values of E opt and ΔE show nonlinear behavior with the compositional parameter. The density and glass-transition temperature of the present glasses also show nonlinear variation, supporting the existence of MAE. The infrared (IR) spectra of the glasses reveal the presence of three- and four-coordinated boron atoms. The specific vibrations of Li–O, Na–O, and K–O bonds were observed in the present IR study.