Lithium Phosphate Glasses Research Articles

Mechanical Properties of Phosphate Glass Optical Fibers

In this work, step‐index 40/125 μm diameter optical fibers produced from two slightly different lithium phosphate glasses were subjected to mechanical characterization. Tensile tests were carried out on fibers with gage length from 10 to 150 mm, allowing for the determination of the failure stress (ranging from ≈200 to 400 MPa) and the elastic modulus (60 GPa). Some tests were also performed with the fiber “immersed” in water; an important subcritical crack growth effect was pointed out, and a fatigue susceptibility parameter (n) equal to 11.4 was determined. The analysis of fracture mirror allows an estimated fracture toughness equal to 0.5 MPa m0.5.

Analysis of Dielectric Properties of Lithium Phosphate Glasses

Dielectric relaxation spectra of lithium phosphate glasses are used to analyze the change of real and imaginary part of complex permittivity including loss tangent of ion conductive glasses. The experimental results getting from a.c. and d.c. electric measurements on Li phosphate glasses are analyzed, discussed and compared. Frequency dependence of the permittivity spectra is found to be consistent with the analysis of d.c. electrical conductivity. The universal a.c. conductivity law (universal dynamic response) for glass ionic conductor was confirmed. Arrhenius graphs constructed from a.c. and d.c. electrical measurements including loss tangent are used to characterize the relaxation processes and transport mechanisms connected with the mobility of conductive ions.

Electrical conductivity of copper lithium phosphate glasses

Copper based oxide glasses are especially interesting for the possibility of ionic-electronic mixed conduction, which has potential applications in energy and switching devices. Accordingly, lithium metaphosphate glasses are investigated within the (100-x) Li2O - xCu2O - 50P2O5 series, where Li+ ions are gradually replaced by copper ions. Based on the changes in glass transition temperature and thermal stability via structural modification, the glasses are shown to be predominantly ionic conductors. In fact, they exhibit signs of classic mixed mobile ion effect (MMIE), a hallmark of ion conduction in glass, which would be due to Li+ and Cu+ ions in the present case.

Effect of Al2O3 nanocrystals on the structural and electrical studies of lithium titanate phosphate glass ceramic matrix

A series of lithium phosphate glass ceramics dispersed with Al2O3 nanocrystals were synthesized via high energy ball milling technique. The milling of Al2O3 powder at room temperature for different milling times is 0, 5, 10, 20, 30, 40, 50 and 60h. The mean particle size distribution was measured using the Scherrer formula for a half width of the diffraction peaks vary from micrometers to ∼24nm for the milling time at 40h. The details of compositions chosen for the present study of investigation are given in the general formula: (100−x) [0.4Li2O–0.1TiO2–0.6P2O5]+x 40h ball milled Al2O3 (where x=0, 2, 4, 6, 8, 10 and 12mol% ) and labeled as LTPAx (where x is the mole% of 40h ball milled Al2O3). The average crystallite size of Al2O3 nanoparticles was measured to be 22nm by transmission electron microscopy (TEM) images, which is in good agreement with the crystallite size calculated from X-ray diffraction (XRD) (24nm) measurements using Scherrer's formula. The frequency dependent conductivity was explained in the light of conducting nanocrystalline phases such as AlPO4, LiTi2(PO4)3, LiAl2P3O7 precipitated in the LTPA samples.

Spectroscopic studies of lithium phosphate, lead phosphate and zinc phosphate glasses containing TiO2: Effect of gamma irradiation

Pristine lithium phosphate, lead phosphate and zinc phosphate glasses and glasses of the same compositions containing TiO2 (0.25→2.5%) were prepared. UV–visible and infrared absorption spectra of the prepared samples were measured before and after gamma irradiation. Optical spectra of these prepared glasses reveal strong UV absorption bands which are attributed to the presence of trace iron impurities in lithium and zinc phosphate glasses while the broad UV bands in lead phosphate glasses were related to absorption of both trace iron impurities and divalent lead ions. The TiO2-containing glasses reveal an extra two visible bands at about 550–580 and 680–740nm due to the transitions 2B2g→2B1g and 2B2g→2A1g of distorted octahedral Ti3+ ions. The effects of gamma irradiation reveal variations, extended in the UV–visible region in the lithium phosphate while with lead phosphate and zinc phosphate samples the variations are restricted to UV spectra. The response to gamma irradiation on optical absorption has been analyzed for both the sharing of all glass constituents including trace iron impurities. Lead and zinc phosphate glasses reveal only induced UV bands from photochemical effect of trace iron impurities while lithium phosphate shows extra induced visible band due to positive holes. The effects of gamma irradiation on the IR spectra are limited to a slight decrease of the intensities for some IR bands. The IR spectra are observed to be slightly affected by the increase of TiO2 indicating the stability of the main phosphate network units and the shielding behavior of titanium ions.

Influence of Immobile Ions on the Length Scale of Ion Transport in Conducting Phosphate Glasses

We have reported the effect of immobile ions on the ion transport in conducting lithium phosphate glasses for different doping concentrations and glass modifier to glass former ratio. The composition dependence of the conductivity of these glasses has been compared with that of the ion conducting silver phosphate glasses. We have obtained microscopic length scales, such as mean square displacement of the center of charge of mobile ions and spatial extent of the localized motion of mobile ions from the conductivity and the dielectric spectra. We have observed a direct correlation between these microscopic length scales of the ion dynamics and the different structural units of the phosphate glass network.

Spectroscopic properties of gamma irradiated TiO2 doped lithium phosphate glasses

Optical absorption spectra of undoped and TiO2-doped lithium phosphate glasses were measured before and after successive gamma irradiation. Undoped lithium phosphate glasses show strong UV absorption, while TiO2-doped samples exhibit surplus two broad visible bands due to the presence of Ti3+ ions in predominant ratio. Gamma irradiation produces UV and visible induced bands but the presence of TiO2 seems to cause some shielding effects towards successive gamma irradiation. Infrared absorption spectral measurements indicate the presence of characteristic phosphate groups and the effect of gamma irradiation is limited to small changes in the intensities of some absorption bands. The experimental results are interpreted on the bases of current views on the structure of the studied host glass in relation to properties studied.

The local structure and magnetic interactions between Fe3+ and V4+ ions in lithium–phosphate glasses

Electron Paramagnetic Resonance (EPR) provides a useful tool not only as a probe of local structure and short range order in glasses, but also of magnetic interactions in the glasses containing suitable magnetic ions. We have analyzed the spectra of xFe2O3·(100 − x)[P2O5·Li2O] and x(Fe2O3·V2O5)·(100 − x)[P2O5·Li2O] glass systems, with 0 < x ≤ 50 mol %. [P2O5·Li2O] stands for 50Li2O·50P2O5 glass composition. For samples x > 50 mol % a study indicates the presence of crystalline α Fe2O3 in the glasses. Observed spectra have resonance lines centered at g ∼ 4.3 and g ∼ 2.0 typical for Fe3+ and V4+ ions present in the oxide glasses. For low contend of transition metal (TM) oxides (Fe2O3 or V2O5·Fe2O3) the spectra present a hyperfine structure typical for isolated V4+ ions. With the increasing of TM content, the EPR absorption signal showing hyperfine structure superposed by a broad line without hyperfine structure characteristic for clustered ions. At high TM content, the vanadium hyperfine structure disappears and only the broad line can be observed in the spectra.

Structure property correlation in lithium borophosphate glasses

To investigate the influence of cation mobility variation due to the mixed glass former effect, 0.45Li(2)O-(0.55-x)P(2)O(5)-xB(2)O(3) glasses (0≤x≤0.55) are studied keeping the molar ratio of Li(2)O/(P(2)O(5)+B(2)O(3)) constant. Addition of B(2)O(3) into lithium phosphate glasses increases the glass transition temperature (T(g)) and number density, decreases the molar volume, and generally renders the glasses more fragile. The glass system has been characterised experimentally by XRD, XPS and impedance studies and studied computationally by constant volume molecular dynamics (MD) simulations and bond valence (BV) method to identify the structural variation with increasing the B(2)O(3) content, its consequence for Li(+) ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms. These studies indicate the increase of P-O-B bonds (up to Y=[B(2)O(3)]/([B(2)O(3)]+[P(2)O(5)])≈0.5 and B-O-B bonds, as well as the decrease of P-O-P bonds and non-bridging oxygens (NBOs) with rising B(2)O(3) content. The system with Y≈0.5 exhibits maximum ionic conductivity, 1.0×10(-7) S cm(-1), with activation energy 0.63 V. Findings are rationalised by a model of structure evolution with varying B(2)O(3) content Y and an empirical model quantifying the effect of the various structural building blocks on the ionic conductivity in this mixed glass former system.

Effect of nanocrystallization on the electrical conduction of silver lithium phosphate glasses containing iron and vanadium

xLi2O·(20-x)Ag2O·20Fe2O3·60P2O5 glasses (x = 0, 5, 10, 15 and 20 mol%) and 5Ag2O·15Li2O·5V2O5·15Fe2O3·60P2O5 glass were prepared by melt-quenching of the reagent mixture at 1000 °C. Glass transition temperature (T g) and crystallization temperature (T c) of these samples were determined by differential thermal analysis (DTA). It proved that T g increased with Li2O content. XRD of as-quenched glasses confirmed their amorphous nature. XRD of samples heat treated for one hour at temperature near their T c, indicated nanocrystals precipitated in the glassy matrix with an average particle size of 35 nm. Mossbauer results revealed that the relative fraction of Fe2 + was decreased with an increasing Li2O content. The isomer shift values of Fe3 + lie in a range of 0.38–0.45 mm s − 1, while those for Fe2 + were 1.10–1.31 mm s − 1. Heat-treated sample of 5Ag2O·15Li2O·5V2O5·15Fe2O3·60P2O5 glass exhibit an enhancement of the electrical conductivity by three orders of magnitude due to the 3d-electron (polaron) hopping from V4 + to V5 + in the “vanadate glass” units.

UV–visible and infrared absorption spectroscopic studies of gamma irradiated tungsten-doped lithium phosphate glasses

Ultraviolet–visible and infrared spectroscopic techniques were employed to investigate the undoped lithium phosphate glass and other samples of the same composition doped with varying WO3 contents. The same spectroscopic properties were remeasured after subjecting the samples to 3 and 6Mrad doses of gamma irradiation on the measured properties. Such combined analytical techniques are expected to give information about the state of tungsten ions in such lithium phosphate glass and justify the effect of gamma irradiation. The work aims to deduce the radiation-induced defects generated through successive gamma irradiation by optical measurements. Also, the study is expected to realize through IR spectroscopy, the main structural building groups and the influence of tungsten ions within the structural vibrational groups of the studied glasses.

UV–visible and infrared absorption spectra of gamma irradiated CuO-doped lithium phosphate, lead phosphate and zinc phosphate glasses: A comparative study

Undoped and CuO-doped lithium phosphate, lead phosphate and zinc phosphate glasses were prepared. UV–visible and infrared absorption spectra of the prepared samples were measured before and after successive gamma irradiation. Experimental optical spectra of the undoped samples reveal strong UV absorption bands, which are attributed to the presence of trace iron impurities in both the lithium and zinc phosphate glasses while the lead phosphate glass exhibits broad UV bands due to combined absorption of trace iron impurities and divalent lead ions. The CuO-doped glasses reveal an extra broad visible band due to Cu 2+ ions in octahedral coordination. The effects of gamma irradiation have been analyzed for both the sharing of all constituent components including trace iron impurities. Infrared absorption spectra of the prepared samples were investigated by the KBr disk technique. The FTIR spectra reveal main characteristic absorption bands due to different phosphate groups. The IR spectra are observed to be slightly affected by the increase of CuO in the doping level (0.2–3%) indicating the stability of the main network units.

Structural characterization of gamma irradiated lithium phosphate glasses containing variable amounts of molybdenum

MoO 3-doped lithium phosphate glasses with varying molybdenum contents were prepared and characterized. Combined UV–visible and infrared (FT/IR) spectroscopic studies were measured before and after gamma irradiation. Experimental results indicate that molybdenum ions occupy different local sites including presence of Mo 3+, Mo 4+ and Mo 5+ with different ratio depending on the host lithium phosphate glass composition and concentration of molybdenum ions. Undoped lithium phosphate glass reveal UV absorption which is related to the presence of unavoidable trace iron impurities. FT/IR spectra were used to identify the main building structural groups present in the studied lithium phosphate glass. The same spectroscopic reutilized techniques were reutilized to identify the induced defects generated after successive gamma irradiation and the influence of molybdenum ions on the irradiation process. Experimental results indicate that molybdenum ions occupy two valences: Mo 5+ and Mo 3+ with the first in dominant percent. The change in the UV, visible and infrared spectral data are discussed in relation to the change in the state of molybdenum ions with glass composition or dopant concentration or network structure evolution caused by the change in glass constituents.

Ultraviolet, visible, ESR, and infrared spectroscopic studies of CeO 2-doped lithium phosphate glasses and effect of gamma irradiation

UV–visible and FTIR spectroscopic properties of some prepared undoped lithium phosphate and CeO 2-doped glasses of the same composition were measured before and after successive gamma ray irradiation. The undoped lithium phosphate glass exhibits strong ultraviolet absorption which is correlated with the presence of trace iron impurities within the raw materials used for the preparation of such glass. The undoped glass shows after gamma irradiation with 2 M rad, the broadness of the UV band with the resolution of two peaks at about 242 nm and 300 nm and the appearance of a small broad band centered at 514 nm. On further exposure to 5 M rad, the base glass exhibits a spectrum consisting of a broad UV absorption with two peaks at about 243 and 384 nm and three visible bands at about 404, 514 and 915 nm. CeO 2-doped samples reveal the broadness of the UV absorption and the appearance of two bands at about 235 and 312 nm. Gamma irradiation on CeO 2-doped glasses produces an extra induced visible band and show obvious shielding effect especially within the visible region but the UV absorption remains unaffected with two peaks at about 240 and 316 nm. Infrared absorption spectra of the prepared glasses reveal characteristic IR vibrations due to characteristic phosphate groups according to the glass composition and the effects of CeO 2 or gamma irradiation are observed to be limited. ESR spectra of the unirradiated CeO 2-doped glass show no specific signals while after gamma irradiation characteristic resonance is observed indicating the appearance of Ce 3+ ions.

Chemical Strengthening of Erbium Phosphate Laser Glass by Ion Exchange

Two kinds of Er-doped lithium phosphate glass have been chemically strengthened by ion exchange in a mixed binary melt of KNO3 and NaNO3 at temperature far below glass Tg. Ion depth profile has been determined with WDS technique. The effect of acid wash on surface morphology, hardness and fracture temperature of glass was investigated. It was found that acid wash following ion exchange could improve the surface morphology and strength of glass. Nevertheless, WDS analysis showed that the acid wash could cause the ion diffusion from glass surface to acid wash liquid, i.e. the back diffusion of K+ and Na+. The results revealed that the back diffusion of K+ was severer than that of Na+ during acid wash and the bond of K+ to glass network was weak.

Lithium ion pathways in LiFePO4 and related olivines

Determining ion transport pathways as regions of low bond valence mismatch represents a simple, reliable way of characterizing ion transport pathways in local structure models, provided that the local structure model captures the essential structural features. The examples of LiFePO4 and other olivine-type mixed conductors discussed here demonstrate the impact of structural disorder on the ion transport pathway and mechanism. The effect of Li′Fe antisite defects on the transition from one- to two-dimensional conduction pathway dimensionality as well the possibility of heterogeneous doping of LiFePO4 by a lithium phosphate glass surface layer are discussed in detail.

Effect of Bi2O3 on the dynamics of Li+ ions in Li2O·P2O5 glasses

Lithium ion transport has been studied in bismuth lithium phosphate glasses in the frequency range 20 Hz–1 MHz and in the temperature range 423–573 K using impedance spectroscopy. The addition of Bi2O3 in Li2O·P2O5 glass is related to the modification of the glass structure and facilitates the Li+ ions migration. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. Conductivity of the present glass system is found to be ionic in nature. The electrical response of the glasses has been studied using both conductivity and electric modulus formalisms. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Nearly identical values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions overcome same energy barrier while conducting and relaxing.

Structure and properties of high Li 2O-containing aluminophosphate glasses

The present study reports on the characterisation of the structure and properties of 50Li 2O· xAl 2O 3·(50 − x)P 2O 5 glasses. The objective of the work has been to study the influence of the alumina content on the properties of lithium phosphate glasses, and the room temperature ionic conductivity in particular, with potential application as solid electrolytes in lithium secondary batteries. The glass formation domain has been also determined, proving that Al 2O 3 can be introduced only up to 5 mol%. The addition of alumina results in the increase of the glass transition temperature and decrease of the molar volume of the glasses. Furthermore, both chemical durability and room temperature conductivity increase as a function of the alumina content. The structure of the glasses has been followed by means of Fourier-transformed infrared spectroscopy (FTIR) and NMR spectroscopy, which has been used to establish the structure–properties relationship.

Strong confinement of PbSe nanocrystals in phosphate glass

Lead selenide quantum dots (QDs) are grown in a novel mixed sodium–lithium phosphate glass. Samples with sharp absorption transition, at 1.48 eV in the near infrared region, and QDs size of 1.5 nm have been prepared. The size of QDs has been calculated from X-ray diffraction and absorption analysis data. The observed high shift in the absorption spectra of PbSe QDs and its size confirm the strong confinement regime of the system. A third harmonic optical phonon of PbSe at 419 cm −1 has been observed in infrared spectra. Transformations in infrared spectra due to growth of nanoparticles have been studied and explained in terms of Pb-withdrawn from the host glass matrix.

Influence of Bi 2O 3 on optical properties and structure of bismuth lithium phosphate glasses

Glasses having compositions xBi 2O 3·(50 − x)Li 2O·50P 2O 5 and xBi 2O 3·(60 − x)P 2O 5·40Li 2O (0 ≤ x ≤ 15, mol%) were prepared by normal melt quenching technique. The density ( D), molar volume ( V M), glass transition temperature ( T g), structure and optical properties have been investigated in order to understand the role of Bi 2O 3 in these glasses. Variations D, V M and T g have been correlated with structural changes in the glass samples. The optical absorption edge ( λ cut-off), optical band gap ( E g) and Urbach energy (Δ E) were determined from the optical absorption spectra of the polished samples recorded in the spectral range from 200 to 3300 nm at room temperature (RT). Variation in these optical parameters has also been associated with the structural changes occurring in these glasses with increase in Bi 2O 3 content. The FTIR spectra have been recorded in the spectral range from 400 to 1400 cm −1. The structural investigations based on these spectra show the rapid depolymerization of phosphate chains with increase in Bi 2O 3 content and formation of P–O–Bi bonds. Also, Bi is incorporated as BiO 6 octahedra in the glass matrix.