Glasses In 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.

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.

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.

Al2O3/K2O-containing non-stoichiometric lithium disilicate-based glasses

The crystallisation kinetics of experimental glasses in 3 different systems: (A) Li2O–SiO2, (B) Li2O–Al2O3–SiO2 and (C) Li2O–K2O–Al2O3–SiO2 were studied under non-isothermal conditions. The DTA results revealed a stronger tendency to crystallisation of binary compositions in comparison to the ternary and quaternary compositions comprising Al2O3 and K2O which present the lower crystallisation, i.e. the crystallisation propensity follows the trend A > B > C. The devitrification process in the Li2O–SiO2 and Li2O–Al2O3–SiO2 systems began earlier and the rate was higher in comparison to that of glasses in the quaternary Li2O–K2O–Al2O3–SiO2 system. Thus, addition of Al2O3 and K2O to glasses of Li2O–SiO2 system was demonstrated to promote glass stability against crystallisation. However, the activation energy for crystallisation was shown to depend also on the SiO2/Li2O ratio with the binary system showing a decreasing trend with increasing SiO2/Li2O ratio, while the opposite tendency was being observed for compositions with added Al2O3 and K2O.

Structural characterisation and thermo-physical properties of glasses in the Li2O–SiO2–Al2O3–K2O system

This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the system Li2O–SiO2–Al2O3–K2O. A glass with nominal composition 23Li2O–77SiO2 (mol%) (labelled as L23S77) and glasses containing Al2O3 and K2O with SiO2/Li2O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics (GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR) depict the role of Al2O3 as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture of Q 3 and Q 4 (Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural features of glasses, phase composition and thermo-physical properties of GCs has been discussed.

Dielectric properties of Li2O–3B2O3 glasses

The frequency and temperature dependences of the dielectric constant and the electrical conductivity of the transparent glasses in the composition Li2O–3B2O3 were investigated in the 100 Hz–10 MHz frequency range. The dielectric constant and the loss in the low frequency regime were electrode material dependent. Dielectric and electrical relaxations were, respectively, analyzed using the Cole–Cole and electric modulus formalisms. The dielectric relaxation mechanism was discussed in the framework of electrode and charge carrier (hopping of the ions) related polarization using generalized Cole–Cole expression. The frequency dependent electrical conductivity was rationalized using Jonscher’s power law. The activation energy associated with the dc conductivity was 0.80±0.02 eV, which was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. Temperature dependent behavior of the frequency exponent (n) suggested that the correlated barrier hopping model was the most apposite to rationalize the electrical transport phenomenon in Li2O–3B2O3 glasses. These glasses on heating at 933 K/10 h resulted in the known nonlinear optical phase LiB3O5.

Models for optical properties in the system Li2O–Na2O–MgO–CaO–TiO2–ZrO2–SiO2

Using experimental design, 15 high titania glasses in the system Li2O–Na2O–MgO–CaO–TiO2–ZrO2–SiO2 were prepared and their refractive indices, dispersions and densities determined. Polynomial models were derived to describe the relationships between properties and glass composition. The refractive index and dispersion models were linear, while the density model required second degree terms for an adequate fit to experiments.

Lithium ion transport in germanophosphate glasses

Glasses in the system Li 2O–GeO 2–P 2O 5 have been prepared using melt quenching route. Li + ion transport has been investigated in these glasses using both d.c. and a.c. conductivity measurements. Arrhenius plots of d.c. conductivity exhibits two different slopes, which has been discussed in the light of cluster-tissue model. A.c. conductivity data has been fitted to single power law. Dielectric relaxation has been analyzed based on the behaviour of moduli. Good collapse on to master plots is observed for both a.c. conductivity and moduli. The behaviour of E dc, s and β are found to be consistent when conductivity mechanism is considered as involving NBO–BO switching as the first step, which is followed by Li + ion migration.

Structure and properties of glasses in the system Li 2O–SnO–B 2O 3

Glasses in the system Li 2O–SnO–B 2O 3 system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B 2O 3 glasses exhibited relatively low glass-transition temperatures ( T g) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of T g indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B 2O 3 binary system.

Lithium ion conductivity and thermal behaviour of glasses and crystallised glasses in the system Li 2O–Al 2O 3–TiO 2–P 2O 5

The effects of Al 2O 3 doping on ionic conductivity and glass stability against crystallisation in the glass system Li 2O–TiO 2–P 2O 5 have been investigated using differential scanning calorimetry and ac impedance spectroscopy. Glass samples of the general molar composition (50+ x)Li 2O: xAl 2O 3:(10−2 x)TiO 2:40P 2O 5 (0≤ x≤4.5) were prepared by air quenching of melts. The highest conductivity at 350°C ( σ 350=2.00×10 −2 S cm −1) and lowest activation energy, E a=0.50 eV, were exhibited by glasses at the x=0.5 composition. This composition also shows the greatest stability against crystallisation ( T c− T g=146°C). The electrical behaviour of the cast, powdered and crystallised glasses was examined. At x=0.5 the conductivity of the crystallised cast glass at room temperature exceeded that of the parent glass. The structural role of Al in the glasses is discussed with respect to variation in the network modifier to network former ratio on substitution for Ti.

Role of PbO in lithium ion transport in Li 2O–PbO–B 2O 3 glasses

A wide range of compositions of glasses in the ternary Li 2O–PbO–B 2O 3 glass system was prepared, and dc and ac conductivity measurements were carried out on these glasses. The presence of lead leads to a decrease in dc conductivities and an increase in the activation energies. This is likely to be due to the increase of the partial charges on the oxygen atoms and to the presence of the lone pair on the Pb atom; both of these factors impede lithium ion motion. The ac conductivity and dielectric behavior of these glasses support such a conjecture.

Fast Li+ ion conduction in Li2O–(Al2O3 Ga22O3)–TiO2–P2O5 glass–ceramics

Fast lithium ionic conducting glass-ceramics have been obtained by heat-treatment of glasses in the systems Li2O–M2O3–TiO2–P2O5 (M = Al and Ga). The glass–ceramics were mainly composed of LiTi2(PO4)3 in which Ti4+ ions were partially replaced by M3+ ions. Considerable enhancement of the conductivity with the substitution of M3+ ions for Ti4+ ions was observed. The maximum conductivity obtained at room temperature was 1.3 × 10−3 S cm−1 for the aluminium system and 9 × 10−4 S cm−1 for the gallium system.

Fast Li + ion conducting glass-ceramics in the system Li 2O–Al 2O 3–GeO 2–P 2O 5

Fast lithium ion conducting glass-ceramics were successfully prepared by heat-treatment of glasses in the system Li 2O–Al 2O 3–GeO 2–P 2O 5. The phase present in the glass-ceramics was LiGe 2(PO 4) 3 in which Ge 4+ ions were partially replaced by Al 3+ ions. Composition dependence of conductivity showed that substitution of Al 3+ ions for Ge 4+ ions resulted in a considerable enhancement in conductivity and in a wide composition range extremely high conductivity over 10 −4 S cm −1 was obtained at room temperature.

Conductivity anomalies in tungstate-phosphate glasses: evidence for an ion-polaron interaction?

Conductivity anomalies are observed in mixed ion-polaron conducting glasses in the system Li 2O: WO 3: P 2O 5. Deep minima in conductivity (reminiscent of the mixed alkali effect) occur when small amounts of Li 2O are introduced into WO 3 − y : P 2 O 5 glasses. By contrast, glasses melted in air are always deep blue in colour, except when large amounts of Li 2O are incorporated. It is suggested that negatively charged polarons (effectively the d-electron located on a W 5 + centre) interact strongly with mobile cations to form uncharged diffusing entities. This may be a general phenomenon in mixed ionic electronic conductors where mobilities of ions and electrons are comparable in magnitude.

The effect of phase separation on short- and intermediate-range order in high-silica Li2O–SiO2 glasses

Wide-angle neutron diffraction measurements have been performed on single-phase and phase-separated high-silica glasses in the system Li2O–SiO2. The structure factors of the single-phase glasses vary modestly with increasing Li2O concentration compared to the changes observed when Na2O or K2O is added to SiO2, and vestiges of the intermediate-range order characteristic of v-SiO2 are retained to 33 mol % Li2O. The structure factors of single-phase and phase-separated glasses are identical to within 1%–2%, indicating that phase separation results in very minor disruptions to local atomic arrangements. When combined with evidence obtained from previous studies, these data indicate that single-phase high-silica glasses in this system contain compositional heterogeneities analogous to those produced by phase separation.

Ionic conductivity of glasses in the system Li 2OP 2O 5TeO 2

Ionic conductivity of Li + conducting glasses with a macromolecular network made of PO 4 tetrahedra and TeO 4 bipyramids have been measured. Glass pellets, according to the formula 0.4 Li 2 O0.6[ xP 2 O 5(1 − x) Te 2 O 4] were obtained by room temperature quenching of melts in a brass mould. The glass forming domain was limited to 0.4 ≤ x ≤ 0.8 and the glass transition temperatures were between 240 °C and 320 °C. Ionic conductivities below T g obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm −1) = 4.3 ± 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.

Conductivity relaxation studies on sol-gel-derived Li2O–SiO2 glasses by a heterogeneous conductor model

Conductivity relaxation spectra of sol-gel-derived glasses in the system Li2O (1 – x) SiO2, with x varying from 0.15 to 0.25, have been analyzed using a heterogeneous conductor model. The latter comprises diagonal layers of phases, one of them being rich in alkali ions and the other deficient in the same. Satisfactory agreement between the experimental data and the theoretical curves has been obtained over the frequency range 100 Hz to 1 MHz. The Kohlrausch–Williams–Watts (KWW) exponent, β, has been calculated from the conductivity spectra for all the glasses. The sol-gel-derived glasses have β values smaller than those obtained in the case of the corresponding melt-quenched ones. The β value is found to be correlated to the conductivity fluctuation in the alkali-rich phase.

Preparation and Ionic Conductivity of the Rapidly-Quenched Glasses in the System Li2O–TiO2–P2O5

Abstract Li+ ion-conducting glasses were prepared in the system Li2O–TiO2–P2O5 by rapid quenching. These glasses had high ionic conductivities of 10−2–10−5 S m−1 at 400 K. The conductivities of these glasses increased and the activation energy for conduction decreased with an increase in the Li2O content of the glasses. At a given Li2O content, the conductivities at 400 K increased with substituting TiO2 for P2O5.

A structural study of rapidly quenched glasses in the system Li2O[sbnd]SiO2

Raman spectra of 4 glasses in the system Li2OSiO2 (41.3 ≦ Li2O ≦ 61.3 mol%) prepared by rapid quenching were measured. The proportions of SiO4 units with 1, 2, 3 and 4 non-bridging oxygens per Si were determined for these glasses from the quantitative analysis of their Raman spectra. X-ray structural analysis of the Li2OSiO2 glasses showed that the average atomic distance of SiO pair was elongated with increasing Li2O content due to the weakening of the SiO bond.