Anharmonicity and fragility in lithium borate glasses

Since the physical properties of lithium borate glasses xLi₂O-(1-x)B₂O₃ (0<x< 0.28) vary over a wide range with the composition, this binary system is particularly suitable for studying the relationship between vibrational anharmonicity and fragility. The density, the linear expansion coefficient, the longitudinal and transverse ultrasonic velocities and their respective temperature coefficients of the velocities are measured, from which the vibrational anharmonicity in lithium borate glasses is evaluated with the help of the Grüneisen parameter at the Debye cut-off frequency and the Anderson-Grüneisen parameter: these two parameters plotted vs. composition have the same characteristics with minima at x≈0.08. The fragility is evaluated from the temperature width of the glass transition; the fragility also shows a minimum at x≈0.08. The presence of minima at x≈0.08 is ascribable to the fact that the crosslinking density between six-membered rings in the glass reaches a maximum at this composition. We show that the anharmonic parameters strongly correlate with the fragility metrics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectroscopic characterization of lithium doped borate glasses

B₂O₃-xLi₂O₃ (x=0, 0.1, 0.5) glasses have been prepared by the Sol-Gel method. The evolution of the composition and the structure of the materials upon thermal treatments are analyzed. Raman spectroscopy measurements reveal that the structure transforms from crystalline to amorphous. After a thermal treatment at 400°C, the materials exhibit a strong luminescence band which disappears upon further heating. In the case of no dopant (x=0) heating at 1150°C results in a Raman spectrum which is almost identical to the one corresponding to bulk B₂O₃ glass obtained by melting and quenching.     

Thermal conductivity of gamma-irradiated ternary borate glasses

The thermal conductivity of a variety of ternary borate glasses before and after gamma irradiation has been measured by the steady-state method at 25°C.The results obtained show that the thermal conductivity decreases with the increase of alkali oxide content or when the glass structure becomes more disrupted. The effect of gamma radiation is believed to result from the creation of disorder and shortening of the phonon mean free path leading to a decrease in the thermal conductivity of the glass.     

Thermal stability of fluorochloroindate glasses

New fluorindate glass compositions have been investigated in order to improve optical transmission as well as thermal properties. Chloride inclusion extends transmission of a fluoride matrix to longer wavelength in infrared region. In the present work thermal parameters of an IZnBS composition, based on InF₃, ZnF₂, BaF₂ and SrF₂, with various amounts of alkaline chlorides were investigated by differential scanning calorimetry. The chloride presence decreased all characteristic temperatures and increased both thermal stability and glass forming ability up to 10% of MCl content, where M=Li, Na, K and Rb. The presence of NaCl promoted glass phase separation. For samples containing same concentration of NaCl, this effect is accentuated for increasing the contents of SrF₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal analysis of glasses for proecological applications

Thermal behaviour and biochemical activity of potassium-silicate-phosphate glasses modified by addition of Ca, Mg, acting as ecological fertilisers of controlled release rate of the nutrients for plants were studied. It has been found that the biochemical activity of silicate-phosphate glasses depends on the nature and the number of components forming the glassy framework and is related to the thermal stability of glass demonstrated by the formation of new compounds during the process of crystallisation. It is proved that these seemingly different properties are determined by the same parameters which are the strengths bonds of glass network-formers and modifiers as well as their chemical affinity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal reactions of solid-state amorphized borates and borate glasses

The properties and course of phase transition of amorphous borates obtained by solid-state thermal and mechanical treatment of hydrated borates and melt quenched glasses with the compositions of these borates were studied. Processes of structural relaxation and crystallization were considered.It was found that different methods of preparation of amorphous borates and the differences in their structural ordering resulting from these methods affect the rate and the mechanism of transformations occurring during their heating.Support for this work was provided by the Polish Committee of Scientific Research (KBN) — grant No. 3 P407 034 06.     

Thermal properties of fluoride glasses and their gel precursors

Xerogels were prepared from zirconium, barium, aluminum, lanthanum and lithium acetates, corresponding to a Li containing ZBLA composition. The study of their thermal properties (DSC, TG/DTG, FT-IR) showed that they might be used as chemically stable precursors in the preparation of fluoride glasses. Hydrofluoric acid in solution was chosen as a mild fluorinating agent. This newly proposed technique of fluorinating allowed to obtain high quality ZBLALi glass which presents the advantage of higher thermal stability and homogeneity in comparison with the glass obtained using individual commercial fluorides.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal analysis of gel-derived bioactive phospho-silicate glasses

Thermal reactions of model phospho-silicate gels of simple composition has been studied. The investigations demonstrate that the kind of compounds introducing P₂O₅ into the gel silicate network, H₃PO₄, PO(OC₂H₅)₃, POCl₃ influence the course and temperature and the xerogel formation. The amount of interstitial water and xerogel porosity is dependent on the cations, amorphous structure modifiers (Ca, Na) used. Thermal analysis curves appear the convenient carriers of informations about the processes in gel pores and the formation of xerogel and glass. This revised version was published online in July 2006 with corrections to the Cover Date.     

Glass transition kinetics of some Se-Te-Ag chalcogenide glasses

Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses. DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperatures. The variation of glass transition temperature T_gwith Ag concentration has been studied. It has been found that T_gdecreases with increase in Ag concentration. The heating rate dependence of T_gis used to evaluate the activation energy of glass transition (DE_t). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DE_thas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of Ag.     

Intense white light luminescent Dy3+ doped lithium borate glasses for W-LED: A correlation between physical,thermal, structural and optical properties

In this article the physical, thermal structural and optical properties of Dy³⁺ doped lithium borate glasses have been studied for white LED application. The emission spectra shows two intense emission bands at around 483 nm and 574 nm corresponds to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions along with one feeble band at 663 nm corresponds to ⁴F_9/2 → ⁶H_11/2 transition. The average lifetime <τ> of Dy³⁺ were found to be about 2.95 and 4.94 ns for blue and yellow emission bands respectively. CIE chromaticity diagram shows glass LBD-4 containing 0.5 mol% Dy₂O₃ with colour co-ordinates x = 0.33 and y = 0.37 have highest emission intensity. These glasses having emission in the white region and thus can be used for bright white LED's and modern white LED bulbs.     

Thermal crystallization studies on Ga−Te glasses

Semiconducting Ga_xTe_100?x (17≤x≤25) glasses have been prepared by melt quenching method and thermal crystallization studies carried out using differential scanning calorimetry. On heating, virgin Ga_xTe_100?x glasses exhibit one glass transition and two crystallization reactions. The first crystallization reaction corresponds to the precipitation of hexagonal Te and the second one to the crystallization of the matrix into zinc blende Ga₂Te₃ phase. If Ga_xTe_100?x glasses are quenched to ambient temperature fromT _crl and reheated, they exhibit the phenomenon of double glass transition.     

DSC studies on sodium phosphate glasses doped with chlorides of Cd,Co and Ag

A number of samples of sodium phosphate glasses doped with Cd/Co or Ag chlorides were prepared and characterized by X-ray diffraction, IR spectral, ion transport and DSC studies. It was found from DSC studies that the glass transition temperature (T _g) and crystallization temperature (T _c) values increased with the increasing concentrations of the dopants Cd/ or Co chlorides. However, the T _g and T _c values were found to decrease when the AgCl was taken as the dopant and the following sequence is observed: T _g(CoCl₂)>T _g(CdCl₂)> T _g(AgCl) T _c(CoCl₂)>T _c(CdCl₂)>T _c(AgCl) These results have been discussed and explained on the basis of changes in the structure of sodium phosphate glassy matrix by the addition of different cations as dopants.The authors are thankful to Prof. M. L. Srivastava, Head, Department of Chemistry, D. D. U. Gorakhpur University, Gorakhpur, and Prof. Suresh Chandra, Department of Physics, B. H. U. Varanasi for providing necessary laboratory facilities and help in carrying out the present work. The financial support from the Department of Science and Technology and University Grants Commission, New Delhi is also gratefully acknowledged.     

Thermal,structural and electrical studies of bismuth zinc borate glasses

Bismuth Zinc Borate glasses with compositions xBi₂O₃–30ZnO–(70 − x)B₂O₃ (where x = 30, 35, 40 and 45 mol %) have been prepared by melt quenching method. These glasses were characterized by X-ray diffraction (XRD), Differential Thermal Analysis (DTA), Fourier Transform Infrared Spectrometer (FTIR) and Broad Band Dielectric Spectrometer (BDS). DTA and FTIR analysis reveals that Non-Bridging Oxygens (NBOs) increase with increase of bismuth content in the glass. Electrical data have been analyzed in the framework of impedance and modulus formalisms. The activation energy for dc conductivity decreases with increase of bismuth concentration. The imaginary part of modulus spectra has been fitted to non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent (β) is found to be almost independent of temperature but slightly dependent on composition.     

Non-debye nature in thermal relaxation and thermal properties of lithium borate glasses studied by modulated DSC

Complex heat capacity, C _p ^*=C _p ^'–iC _p ^', of lithium borate glasses xLi₂O·(1–x)B₂O₃ (molar fraction x=0.00–0.30) has been investigated by Modulated DSC. We have analyzed the shape of C _p ^* by the Cole-Cole plot, performed fitting by the Havriliak-Negami equation, and then determined the parameters related to the non-Debye nature of thermal relaxation. Moreover, the concentration dependence of the thermal properties has been investigated. Glass transition temperatures become higher with the increase of molar fraction of Li₂O and shows the board peak around x=0.26. Temperature ranges of glass transitions become narrower with the increase of Li₂O concentration.     

Thermal and structural studies of nanocrystallization of oxyfluoride glasses

The influence of fluorine content on the structure and crystallization of oxyfluoride glasses from the Na₂O–Al₂O₃–SiO₂–LaF₃ system was studied by DTA/DSC, XRD, FTIR and SEM methods. It has been found that the increase in the fluorine content in the structure of oxyfluoride glasses causes the increase of the flexibility of their structure, which inhibits the process of crystallization of the silicate- aluminium matrix. Simultaneously the ability of the glass for LaF₃ crystallization, which shows a multistage character, is increasing. Analysis of the local atomic interactions in the structure of glasses has been used to explain the course of the crystallization.     

Dielectric studies of As-Se glasses

Dielectric constants and loss tangents of As-Se glasses have been measured between 300 K and the respective glass transition temperatures and between 1 kHz and 20 kHz. The variation of dielectric constants has been interpreted in terms of both heteropolarity of bonds and average bond energies employing a chemically ordered network model. Various contributions to total molar polarizations have been estimated. Rapid rise of loss tangent in the vicinity of glass transitions has been interpreted in terms of rapid increase; of d.c. conductivity. Communication No. 108 from Solid State and Structural Chemistry Unit.     

Thermal and Mechanical Properties of Lithium Borate Glasses in Relation to the Glass Structure

In lithium borate glasses RLi₂OB₂O₃ (0R<0.4), the following experimental results were obtained: 1. The density increases monotonically with increasing R. 2. Both velocities of longitudinal and transverse ultrasonic waves increase monotonically with increasing R. 3. The elastic constants such as bulk modulus and Young's modulus increase monotonically with increasing R. 4. The linear expansion coefficient shows a broad minimum at around R=0.25. 5. The Poisson ratio shows a minimum at around R=0.10 and a maximum at around R=0.20. 6. Each of the temperature coefficients of velocities for longitudinal and transverse ultrasonic waves shows a sharp minimum at R=0.10 and a sharp change in slope at R=0.20. The experimental results 1, 2 and 3 can be ascribed to a change in short-range order groups. The experimental result 4 is ascribable to the most compact configuration at around R=0.25. The experimental results 5 and 6 are ascribable to a change in crosslink between six-membered borate rings.This revised version was published online in November 2005 with corrections to the Cover Date.     

Structure inhomogeneities of medium-range order in fluorozirconate glasses

Images of cleaved surfaces were obtained for 53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å.     

Thermal Behaviour of Silicate-Phosphate Glasses in Relation to Their Biochemical Activity

Glasses of theK₂O–MgO–CaO–SiO₂ and K₂O–MgO–CaO–P₂O₅–SiO₂ systems with microelements (Fe, Mo, Zn, B, Mn, Cu) were obtained by melting of apatite and serpentinite rocks, K₂CO³ and oxides of appropriately metals mixtures. The amorphous state of glasses and the structural changes during their heating were determined by RDF and DTA/DSC methods. The solubility of the glasses in 2 mass% citric acid solution was studied by chemical analysis (ICP-AES, EDS) and SEM observations.It has been found that the biochemical activity of silicate-phosphate glasses depends on the content of P₂O₅ and K₂O in their framework and is related to crystallisation ability of these glasses.This revised version was published online in November 2005 with corrections to the Cover Date.     

EXAFS studies of cobalt oxides and oxide glasses

The exafs of Co²⁺ has been studied in rare earth cobaltites and in sulphate and borate glasses. It has been found that the environment of Co²⁺ ions is very similar in these cases. It appears feasible to study local structures in glasses using probe ion exafs. Communication No. 151 from the Solid State and Structural Chemistry Unit.