Sodium Borate Glasses Research Articles

Low-temperature specific heat in caesium borate glasses

Low-temperature specific heat measurements (1.5–25 K) performed on caesium borate glasses at different concentrations have pointed out the presence of an excess specific heat, C p, over the Debye contribution. In a plot C p/T 3 vs. T, it appears as a bump, temperature location of which is almost unchanged whereas its intensity increases with caesium concentration. A comparison with the specific heat in sodium borate glasses has revealed highly dissimilar low-energy dynamics, despite the same structural units building up the borate matrix. The different behaviours observed have been related to the peculiar structural changes that the inclusion of alkaline cations cause in the mesoscopic length scale where the effects of the medium-range order (MRO) are usually observed. It is believed that the particularly open structure of caesium glasses assures a very low frequency for the local oscillations of Cs+ ions that, consequently, rule the vibrational dynamics in the frequency region of the boson peak by their localized character.

Influence of water on the structure and kinetics of structural relaxation in sodium borate glasses

The influence of the water content on the microinhomogeneous structure of sodium borate glasses containing 2.5 and 5.0 mol % Na2O and on the kinetics of structural relaxation in vitreous boron oxide and sodium borate glasses is studied by the small-angle X-ray scattering (SAXS) technique. It is demonstrated that an increase in the water content brings about an increase in the size of the inhomogeneity regions and a decrease in the mean square of the difference between the electron densities 〈(Δρ)2〉 for the microinhomogeneous structure. The inference is made that water has a catalytic effect on the aggregation of alkali borate structural units. The kinetic dependence of the intensity of small-angle X-ray scattering by thermal density fluctuations is described by the Kohlrausch equation. The exponent β in the Kohlrausch equation is close to 1.0 for “dry” glasses and decreases to 0.5 for glasses containing 0.7–1.0 mol % H2O.

Femtosecond laser induced PL change in Sm-doped sodium borate glass and 3D optical memory

We report on a femtosecond laser-induced photoluminescence (PL) change in Sm-doped sodium-borate glass and its potential application to three-dimensional optical memory. Irradiation with a femtosecond pulsed laser (800 nm, 1 kHz, 100 fs) induced a new PL peak near 682 nm, resulting from the photoreduction of Sm ions from Sm 3+ to Sm 2+. This makes it possible to readout the stored data by detecting the new PL peak as a signal. Multilayer patterns of various dot sizes and interlayer spacings were fabricated by femtosecond pulsed laser. These patterns were read out by a fluorescent confocal microscope which detected the emission at 682 nm as a signal. Here we discuss the feasibility of 3D optical memory by use of PL change in Sm-doped sodium borate glass.

Laser–induced defect centers and valence state change of Mn ions in sodium borate glasses

In this report, an ultrafast laser was used to produce persistent change of valence states of Mn ions in sodium borate glasses. Glass composition of sodium borate in this study was 85B 2O 3–15Na 2O. We observed a broad emission at 600 nm of the transition 4T 1– 6A 1 of doped Mn 2+ ions with excitation at 325 nm in an unirradiated area. Femtosecond laser irradiation produced additional strong blue emission at 440 nm and reduced the emission intensity from Mn 2+ ions. The irradiation produced the absorption band of Mn 3+ at 550 nm, resulting in color change of the glass. The blue band was measured as a function of irradiation exposure for samples with various concentrations of Mn ions. The valence state change of Mn 2+ to Mn 3+ was suppressed in Mn and Cr codoped glasses.

Temperature and pressure dependence of the homogeneous width of 7F 0– 5D 0 electronic transition in Sm 2+-doped sodium borate glass

The homogeneous width Γ h of 7F 0↔ 5D 0 transition in Sm 2+ ions doped into sodium borate glass was determined at T=5–293 K under P=1 bar and at T=5, 80 and 120 K under various P up to 8 kbar. The line width Γ h was obtained from spectral hole burning (SHB) and time-resolved resonant fluorescence line narrowing (FLN) experiments. It was found that at P=1 bar the T-dependence of Γ h changes from Γ h( T)∝ T 2 (quadratic) for T<20 K to Γ h( T)∝ T (linear) for T>20 K. Under pressure, Γ h grows slightly at all three T values studied (at 80 K by 1.2%/kbar and at 120 K by 1.6%/kbar in the range 0–8 kbar). Possible mechanisms to explain the observed T- and P-dependences of Γ h are briefly discussed.

Femtosecond laser-induced reduction in Eu-doped sodium borate glasses

In this work, we report permanent reduction of Eu 3+ to Eu 2+ in sodium borate glasses by irradiation of near-infrared femtosecond laser. Glass composition of sodium borate was 85B 2O 3–15Na 2O. The glasses were doped with 0.05, 0.1, and 0.5 mol% Eu 2O 3. Absorption and fluorescence dynamics were studied to investigate valence state change of europium ions and the energy transfer between Eu 2+ and Eu 3+ ions. As the femtosecond laser intensity or exposure time increases, the emission band at 400 nm becomes stronger. However, the photoreduction efficiency decreases as the dopant concentration increases. We discuss the photoreduction mechanism under multiphoton absorption.

Specific features of the kinetics of structural relaxation in microinhomogeneous glasses

The kinetics of structural relaxation in vitreous boron oxide and sodium borate glass containing 5.5 mol % Na2O during isothermal treatment at a number of temperatures after cooling from high temperatures and a sharp increase in the temperature of samples stabilized at T < Tg for different times is studied by the small-angle X-ray scattering (SAXS) technique. It is shown that, as the fictive temperature of samples approaches the temperature at which the supercooled liquid transforms into a noncrystalline solid state, the times of development of a structural inhomogeneity that arises in the samples after a drastic increase in the temperature increase considerably in a narrow temperature range (1–2 K). The intensity of small-angle X-ray scattering by a micro-inhomogeneous structure formed in the course of relaxation processes in chemically inhomogeneous glasses substantially exceeds the SAXS intensity observed during structural relaxation of vitreous boron oxide. This is associated with the increase in the sizes of structural inhomogeneity regions in the matrix in heterogeneous samples as compared to the sizes of similar regions in homogeneous glasses. Stresses arising in heterogeneous samples during structural relaxation are responsible for the interference effects that substantially affect both the SAXS intensity at angles close to zero and, correspondingly, the light scattering intensity.

The influence of water on the structure and glass transition of sodium borate supercooled liquids from the small-angle X-ray scattering data

Sodium borate glasses containing 5.5, 15, and 25 mol % Na2O are synthesized under different conditions (different temperatures and times of heat treatment, treatment under vacuum) and studied by the small-angle X-ray scattering (SAXS) technique. The temperatures of the glass transition and the transition from the supercooled liquid state to the noncrystalline solid state are determined from the temperature dependences of the SAXS intensity. It is revealed that a decrease in the water content leads to an increase in the glass transition temperatures and to an increase in the SAXS intensity in the case of glasses containing 15 and 25 mol %. It is assumed that this behavior can be associated with the increase in the isothermal compressibility.

Optical hole burning studies in europium doped oxide glasses

Europium doped sodium borate, silicate, borosilicate, germanate and tellurite glasses have been prepared by melt quenching technique. Optical spectroscopy techniques were used to characterize the divalent and trivalent ions. Optical hole burning technique was used to characterize rare-earth ion doped glasses for optical data storage. The hole burning mechanisms, which depend on the glass composition and the preparation methods used, are discussed.

포토폴리머와 희토류이온이 첨가된 유리에서의 이광자흡수를 이용한 광정보저장

We studied feasibility of three-dimensional optical memory by utilizing femtosecond laser-induced changes of transmission in photopolymers and photoluminescence in Eu and Sm ion doped sodium borate glasses. We produced transmission change by two photon absorption and obtained sub-Um size spots in photopolymers using 780 nm modelocked Ti-sapphire laser pulses. We also changed valence state of Eu and Sm ions by multi-photon absorption and achieved sized spot formation in Sm-doped glasses.

Variation of the oxidation state of iron in sodium borate glasses caused by the external magnetic field applied during sample preparation

Sodium borate glass containing iron and cobalt oxides, (Na2B4O7)0.750(Fe2O3)0.125(CoO2)0.125 was prepared by melting the reagent mixture at 1000 °C for half an hour in air. Part of the melt was poured onto a stainless steel plate kept at room temperature under an external magnetic field (about 1 kOe). For comparison, the other part of the melt was also poured on a stainless steel plate at room temperature without applying the external magnetic field. Room-temperature Mössbauer and magnetic susceptibility measurements of the pulverized glass samples at one-week interval, starting from the time of preparation, show a gradual change of the oxidation state of iron with time from Fe(II) to Fe(III) for the sample which was subjected to an external magnetic field; sample (A). The sample prepared without the magnetic field, sample (B), showed no change of the oxidation states of iron with time; it showed almost a constant value of the oxidation state as indicated from the isomer shift values in the Mössbauer spectra and from the magnetic susceptibility measurement. Effect of the magnetic field on the redox of iron in the melt is discussed together with the time-dependent oxidation state of the iron in sodium borate glasses.

Optical absorption and fluorescence properties of Er3+ in sodium borate glass

Spectroscopic properties of Er3+ ions in sodium borate glass have been studied. The indirect and direct optical band gaps (Eopt) and energy level parameters (RacahE 1, E2 and E3), spin-orbit (ξ4f) and configurational interaction (α)) are evaluated. Spectral intensities for various absorption bands of Er3+ doped sodium borate glass are calculated. Using Judd-Ofelt intensity parametersΩ 2, Ω4, Ω6, radiative transition probabilities (A), branching ratios (β) and integrated absorption cross sections (Σ) are reported for certain transitions. The radiative lifetimes (τR) for different excited states are estimated. From the fluorescence spectra, the emission cross section (σP) for the transition,4I13/2 → 4I15/2 is reported.

Three-dimensional optical memory using photoluminescence change in Sm-doped sodium borate glass

The feasibility of three-dimensional (3D) optical memory has been demonstrated by utilizing the photoluminescence (PL) spectrum change in a Sm-doped fluoride glass [K. Miura, J. Qiu, S. Fujiwara, S. Sakasuchi, and K. Hirao, Appl. Phys. Lett. 80 2263 (2002)]. We here report on a femtosecond laser-induced PL change in a Sm-doped sodium borate glass that is easier to synthesize and its potential application to 3D memory. Irradiation with a femtosecond pulsed laser (800 nm, 1 kHz, 100 fs) induced a PL peak near 682 nm, resulting from the photoreduction of the Sm ions. A multilayer pattern (bit size=1μm,layer separation=8μm) formed by femtosecond laser irradiation was read out by a reflection-type fluorescent confocal microscope, which detected the emission at 682 nm as a signal. High-contrast pattern images were obtained without crosstalk.

IR spectroscopic study of water in the structure of binary alkali borate glasses

In our earlier works [9‐12], the influence of water in the structure of alkali borate glasses on their physicochemical properties was studied using IR absorption spectroscopy in the range of stretching vibrations of hydroxyl groups. However, most attention in consideration of binary alkali borate glasses was concentrated on the problem associated with the quantitative determination of the water content in glasses. The effect of the glass composition and synthesis conditions on the forms of water in the structure of these glasses was not analyzed. On the other hand, investigations of twoalkali borate glasses [11, 12] revealed that there is a correlation between the content of water in the form of so-called bound hydroxyl groups with an absorption maximum at 3.5‐3.7 µ m and the manifestation of the mixed alkali effect in the properties of these glasses. This finding is important for understanding the mechanism of manifestation of the mixed alkali effect in the properties of borate glasses and illustrates the relation of the glass composition to the ratio between two forms of hydroxyl groups in the glass structure. The revealed correlation is of special interest because a number of authors [13, 14] believe that the presence of bound hydroxyl groups is not characteristic of the structure of alkali borate glasses. In the present work, we investigated how the synthesis conditions and the glass composition affect the spectral absorption in the range 2.5‐4 µ m due to the presence of structurally bound water in binary sodium and potassium borate glasses.

Cation environments and spatial distribution in Na2O–B2O3 glasses: New results from solid state NMR

The spatial distribution of the sodium ions in sodium borate glasses with composition (Na2O)x(B2O3)1+x (0 < or = x < or = 0.30) has been studied by complementary high resolution and dipolar solid state NMR experiments. 23Na-23Na homonuclear dipole-dipole couplings measured via 23Na spin echo decay spectroscopy indicate the absence of cation clustering at all compositions. Consistent with this result, 11B{23Na} rotational echo double resonance (REDOR) measurements indicate that the trigonal BO3/2 groups and the four-coordinate BO4/2(-) units experience 23Na local dipolar fields of similar magnitudes. Both experiments suggest a sodium spatial distribution that is essentially statistical. The dipolar coupling data are modelled consistently on the basis of a cubic NaCl-type lattice, from which an appropriate number of sodium ions have been randomly removed to reproduce the Na+ number density of the glass under consideration. In addition, at very low Na+ concentrations (x < 0.12) a compositionally independent local sodium environment is formed, which is characterized by a significant Na+ BO4/2(-) pair correlation involving an internuclear distance of 316 pm. For higher sodium oxide contents (x > 0.20) the 23Na-23Na dipole-dipole couplings suggest a gradual transition from a random towards a more homogeneous sodium distribution.

Publisher's Note: Isothermal aggregation of Ag atoms in sodium borate glass [Phys. Rev. B70, 054106 (2004)

Publisher's Note: Isothermal aggregation of Ag atoms in sodium borate glass [Phys. Rev. B70, 054106 (2004)

Dependence of sodium borate glass structure on depth from the sample surface

Structural properties of sodium borate glasses with nominal composition 0.3Na2O–0.7B2O3 were investigated as a function of depth from the sample surface by employing infrared specular reflectance spectroscopy. To this aim, cylindrical samples of 2mm in thickness were prepared from the same batch by quenching the melt into appropriate shapes and surface layers were subsequently removed by appropriate polishing. The analysis of the mid infrared spectra revealed the presence of boron–oxygen triangles, BØ3, BØ2O−, and tetrahedra, BØ4-, as the short-range order units building the glass network (Ø denotes an oxygen atom bridging two boron centers). It was found that the relative population of the BØ4- tetrahedral units increases with thickness of the removed layer, and this structural change was shown to affect also the distribution of network sites hosting the sodium ions. In particular, the spectral weight of the asymmetric far infrared absorption profile was found to increase gradually towards lower frequencies with thickness of the removed layer. These findings were discussed in terms of cooling rate gradients from the surface to the core of the glass sample.

Isothermal aggregation ofAgatoms in sodium borate glass

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Effect of TiO 2 on electron paramagnetic resonance, optical transmission and dc conductivity of vanadyl doped sodium borate glasses

Glass systems with composition xTiO 2·(30− x)Na 2O·70B 2O 3 (series I) and xTiO 2·(70− x)B 2O 3·30Na 2O (series II) containing 2 mol% V 2O 5 have been prepared (0≤ x≤7, mol%) by normal melt-quenching. The electron paramagnetic resonance (EPR) spectra of VO 2+ ions have been recorded in the X-band (∼9.13 GHz) at room temperature. Spin Hamiltonian parameters, g ||, g ⊥, A ||, A ⊥, the dipolar hyperfine coupling parameter ( P) and the Fermi contact interaction parameter ( K) have been calculated. The increase in Δ g ||/Δ g ⊥ with increase in TiO 2 content in series I shows that the octahedral symmetry of V 4+O 6 complex is reduced, whereas in series II the octahedral symmetry is improved with increase in x. The decrease in P, in both the series, indicates that the 3d xy orbit expands with increase in mol% of TiO 2. The molecular orbital coefficients, α 2 and γ 2 have been calculated by recording the optical transmission spectra in the range 500–850 nm. α 2 and γ 2 increase with increase in x in both the series, which indicates that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity σ, decreases and activation energy, W increases with increase in TiO 2:Na 2O ratio whereas with increase in TiO 2:B 2O 3 ratio the variation in σ and W is within experimental error.

Effect of TeO 2 on the elastic moduli of sodium borate glasses

Sodium borate glass containing tellurite as Te x Na 2−2 x B 4−4 x O 7−5 x with x=0, 0.05, 0.15, 0.25 and 0.35 have been prepared by rapid quenching. Ultrasonic velocity (both longitudinal and shear) measurements have been made using a transducer operated at the fundamental frequency of 4 MHz at room temperature. The density was measured by the conventional Archimedes method. The elastic moduli, the Debye temperature, Poisson's ratio, and the parameters derived from the Makishima–Mackenzie model and the bond compression model have been obtained as a function of TeO 2 content. The monotonic decrease in the velocities and the elastic moduli, and the increase in the ring diameter and the ratio K bc/ K e as a function of TeO 2 modifier content reveals the loose packing structure, which is attributed to the increase in the molar volume and the reduction in the vibrations of the borate lattice. The observed results confirm that the addition of TeO 2 changes the rigid character of Na 2B 4O 7 to a matrix of ionic behaviour bonds (NBOs). This is due to the creation of more and more discontinuities and defects in the glasses, thus breaking down the borax structure.