Crystallization and conductivity of 2CaO–La2O3–5P2O5 glass–ceramic with Al2O3 addition

Al₂O₃ was added to a 2CaO–La₂O₃–5P₂O₅ metaphosphate, to replace 10% of the Ca²⁺ ions by Al³⁺, forming a phosphate with the nominal composition 1.8CaO–0.1Al₂O₃–La₂O₃–5P₂O₅. The effect of Al₂O₃ addition and heat treatment on the microstructure and conductivity of the resulting glass–ceramics was investigated by XRD, SEM, TEM, and AC impedance spectroscopy. Upon transformation from glass to glass–ceramic, conductivities increased significantly. The glasses were isochronally transformed at 700 and at 800 °C for 1 h or 5 h, in air, following heating at 3 or 10 °C/min. With Al₂O₃ addition, after a heat treatment at 700 °C, 100–300 nm nano-domains of LaP₃O₉ crystallized from the glass matrix. Annealing at 800 °C produced a further order of magnitude conductivity increase for the Al-free glass, but less so for the Al-containing glass.     

Optical and IR study of Li2O–CuO–P2O5 glasses

Infrared (IR) and UV spectra of ternary Li₂O–CuO–P₂O₅ glasses in two series Li₂O(65−X)%–CuO(X%)–P₂O₅(35%), X = 20, 30, 40 and Li₂O(55−X)%–CuO(X%)–P₂O₅(45%), X = (10, 20, 30) were studied. Infrared (IR) investigations showed the metaphosphate and pyrophosphate structures and with increase of CuO content in metaphosphate glass, the skeleton of metaphosphate chains is gradually broken into short phosphate groups such as pyrophosphate. IR spectra showed one band at about 1,220 and 1,260 cm⁻¹ for P₂O₅(35%) and P₂O₅(45%) series, respectively, assigned to P=O bonds. For CuO additions ≤20 mol%, the glasses exhibit two bands in the frequency range 780–720 cm⁻¹ which are attributed to the presence of two P–O–P bridges in metaphosphate chain. But for CuO addition ≥30 mol%, the glasses exhibit only a single band at 760 cm⁻¹ which is assigned to the P–O–P linkage in pyrophosphate group. In optical investigations, absorption coefficient versus photon energy showed three regions: low energy side, Urbach absorption, and high energy side. In Urbach’s region, absorption coefficient depends exponentially on the photon energy. At high energy region, optical gap was calculated and investigations showed indirect transition in compounds and decreases in optical gap with increases of copper oxides contents that is because of electronic transitions and increasing of nonbridging oxygen content.     

Microstructure and varistor properties of ZnO–V2O5–MnO2 ceramics with Ta2O5 addition

The effect of Ta₂O₅ addition on microstructure, electrical properties, and dielectric characteristics of the quaternary ZnO–V₂O₅–MnO₂ vaistor ceramics was investigated. Analysis of the microstructure indicated that the quaternary ZnO–V₂O₅–MnO₂–Ta₂O₅ ceramics consisted of mainly ZnO grain and minor secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, TaVO₅, and Ta₂O₅. As the amount of Ta₂O₅ increased, the sintered density increased from 94.8 to 97.2% of the theoretical density (5.78 g/cm³ for ZnO), whereas the average grain size decreased from 7.7 to 6.0 μm. The ceramics added with 0.05 mol% Ta₂O₅ exhibited the highest breakdown field (2715 V/cm) and the highest nonlinear coefficient (20). However, further increase caused α to abruptly decrease. The Ta₂O₅ acted as a donor due to the increase of electron concentration in accordance with the amount of Ta₂O₅. The donor concentration increased from 1.97×10¹⁸ to 3.04×10¹⁸cm^?3 with increasing the amount of Ta₂O₅ and the barrier height exhibited the maximum value (0.95 eV) at 0.05 mol% Ta₂O₅.     

Structure,dielectric and bioactivity of P2O5–CaO–Na2O–B2O3 bioactive glass

Bioactive phosphate glasses have been widely investigated for bone repair. Phosphate glass system of 47P₂O₅–30.5CaO–(22.5?x)Na₂O–xB₂O₃ has been prepared by melt quenching technique. From the Raman analysis, it is confirmed that phosphate network form metaphosphate structure. Bioactivity of the glass is studied by immersing the prepared glass in simulated body fluid (SBF). All the glasses exhibited bioactivity after soaking in SBF. Addition of B₂O₃ to the glass by replacing the Na₂O produces considerable effect on the dielectric and bioactivity of the glass. Ion dynamics are also analyzed through imaginary modulus and imaginary dielectric permittivity.     

EPR and Magnetic Susceptibility of Na2O–CuO–P2O5 Glasses

Abstract

(50?x/2)Na₂O–xCuO–(50?x/2)P₂O₅ glasses (x=1, 5, 15, or 30 mol%) have been prepared and characterized by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. The shape of the Cu²⁺ EPR spectrum depends on the Cu content, and the corresponding computer simulations suggest that the Cu²⁺ ions occupy two different sites in these glasses: one of them is preponderant at low Cu content and the other is preponderant at high content, in which the Cu²⁺–Cu²⁺ interactions are more important. From EPR parameters, it was found that for the site at low content, the covalency of copper ion bonding with the surrounding ligands is appreciable. The magnetic susceptibility data appear to follow the Curie–Weiss law (χ=C/(T?θ_p)) with negative paramagnetic Curie temperature θ_p indicating antiferromagnetic interactions between Cu²⁺ ions that are more significant in the samples with high Cu content, in agreement with EPR results.     

Proton conductivity in sol–gel-derived P2O5–TiO2–SiO2 glasses

The sol–gel method was applied to prepare the P₂O₅–TiO₂–SiO₂ glasses with high proton conductivities and chemical stability. The glasses were prepared by the reaction of the Ti- and Si-alkoxides with PO(OCH₃)₃ or H₃PO₄, followed by heating at 600 °C. The obtained glasses were porous, the average pore diameter of which was <2 and 4 nm for glasses prepared using PO(OCH₃)₃ and H₃PO₄, respectively. The phosphorous ions, occurring as PO(OH)₃ in the TiO₂-free glass, were polymerized with one or two bridging-oxygen ions per PO₄ unit with the increasing TiO₂ content. Despite the P₂O₅–SiO₂ binary glasses exhibiting high conductivities of ∼10⁻² S/cm at room temperature, they also dissolved after immersing for 24 h in water. The chemical stability of these glasses increased significantly on the addition of TiO₂.     

Optical properties of glasses in the Li2O–MoO3–P2O5 system

Glasses xLi₂O–(50-x)(MoO₃)₂–50P₂O₅ with x = 10, 20, 30, and 40 mol% were prepared and their optical and electrical properties were investigated. Analysis of the IR spectra revealed that the Li⁺ ions act as a glass modifier that enter the glass network by breaking up other linkages and creating non-bridging oxygens in the network. The optical absorption edge of the glasses was measured for specimens in the form of thin blown films and the optical absorption spectra of those were recorded in the range 200–800 nm. From the optical absorption edges studies, the optical band gap (E _opt) and the Urbach energy (E _e) values have been evaluated by following the available semi-empirical theories. The linear variation of (αhν)^1/2 with hν, is taken as evidence of indirect interband transitions. The E _opt values were found to decrease with increasing Li₂O content by causing increase in the number of non-bridging oxygens in network. The Urbach tail analysis gives the width of localized states between 0.48 and 0.74 eV.     

Ultrasonic,FTIR and thermal investigations of SiO2–Na2O–CaO–P2O5 glasses doped with CeO2

The longitudinal and shear ultrasonic wave velocities for different compositions of SiO₂–Na₂O–CaO–P₂O₅ glasses were measured at room temperature (305 K) using a pulse-echo method at a frequency of 4 MHz. The elastic moduli, Poisson's ratio, microhardness, Debye temperature and other ultrasonic parameters were obtained from experimental data and analyzed using bond compression theory. By calculating the number of network bonds per unit volume, the average stretching constant, and the average ring size, information about the structure of the glass can be deduced. Structural changes after doping with CeO₂ were investigated by FTIR spectroscopy, and by measurements of the thermal expansion coefficient, glass transition and softening temperature to throw more light on the characterization of these glasses.     

Synthesis and properties of MoO3–V2O5–PbO glasses

Lead vanadate glasses of the system xMoO₃–50V₂O₅–(50-x)PbO (0 ≤ x ≤ 25 mol. %) were synthesized and studied by FTIR and ultrasonic spectroscopy and differential scanning calorimetry to investigate the role of MoO₃ content on their atomic structure. The elastic properties and Debye temperatures of the glasses were investigated using sound velocity measurements at 4 MHz. The activation energy for the glass transition was derived from the dependence of the glass-transition temperature (T_g ) on the heating rate. Similarly, the activation energy of the crystallization process was also determined. According to the IR analysis, the vibrations of the vanadate structural units are shifted towards higher wavenumbers on the formation of bridging oxygens. The change of density and molar volume with MoO₃ content reveals that the molybdinate units are less dense than the lead oxide units. The observed compositional dependence of the elastic moduli is interpreted in terms of the effect of MoO₃ on the coordination number of the vanadate units. A good correlation was observed between the experimentally determined elastic moduli and those computed according to the Makishima–Mackenzie model. It is assumed that MoO₃ plays the role of a glass former by increasing the activation energy for the glass transition and the activation energy for crystallization and by increasing both the thermal stability and the glass formation range of the vanadate glasses.     

Fe2P2O7 and Fe2P4O12 studied between 5–800 K

Mössbauer spectra of triclinic Fe₂P₂O₇ indicate the existence of two crystallographic metal positions in the structure. In the paramagnetic region the two Mössbauer doublets are closely overlapping. The magnetic transition takes place at ≈ 21 K and the saturated fields are around 12 tesla for the two positions. In monoclinic Fe₂P₄O₁₂ the two octahedrally coordinated metal positions give quite different quadrupole splittings (1.5 and 3 mm/s at room temperature) and hyperfine field values (42 and 12.5 Tesla at 5 K). The transition temperature is at ≈ 18.5 K.     

Thermal analysis and infrared study of Nb2O5–TeO2 glasses

Tellurite glasses of the xNb₂O₅–(100–x) TeO₂, (3 ≤ x ≤ 20 mol%) system have been prepared and studied by IR spectroscopy and differential thermal analysis to explore the role of Nb₂O₅ on their structure. IR analysis indicates that NbO₆ transforms TeO₄ units into tellurite structural TeO₃ units, with a shift of lattice vibrations towards higher wavenumbers. The stretching force constant of the tellurite structural units increases with Nb₂O₅ content, a feature that is attributed to the higher bond strength and higher coordination number of Nb₂O₅ relative to TeO₂. The crystallization kinetics has been studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results are analyzed, and both the activation energy of the crystallization process and the crystallization mechanism are characterized. The thermal stability of these glasses are characterized in terms of characteristic temperatures, such as the glass-transition temperature, T _g, the temperature of onset of crystallization, T _in, the temperature corresponding to the maximum crystallization rate, T _p, and two kinetic parameters, K(T _g) and K(T _p). The results reveal that thermal stability increases with increasing Nb₂O₅ content. XRD diffraction of the studied glasses indicates the presence of microcrystallites of α-tellurite, γ-telluride, Nb₂Te₄O₁₃ and an amorphous matrix.     

Specific Features of the Local Structure and Transport Properties of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 Crystals

Optics and Spectroscopy - The specific features of the local structure of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 crystals are revealed by optical spectroscopy using the Eu3+...     

Spectroscopic characterization of Tm3+:TeO2–K2O–Nb2O5 glasses for 2-μm lasing applications

We have performed detailed experiments to investigate the spectroscopic properties of a new type of tellurite based host doped with thulium: Tm₂O₃:(0.70)TeO₂–(0.15)K₂O–(0.15)Nb₂O₅ having Tm₂O₃ concentrations of 0.125, 0.25, 0.5, and 1.0 mol%. By performing a Judd–Ofelt analysis of the absorption bands, we obtained average radiative lifetimes of 2.57±0.20 and 0.35±0.01 ms for the ³H₄ and ³F₄ levels, respectively. Furthermore, we also observed that an increase in the Tm₂O₃ concentration from 0.125 to 1.0 mol% results in a decrease of the measured fluorescence lifetime from 814 to 439 μs and from 258 to 47 μs for the ³H₄ and ³F₄ levels, respectively, due to efficient non-radiative decay. The highest quantum efficiency of 32% was obtained for the sample doped with 0.125 mol% Tm₂O₃ for the ³H₄ level. Results show that cross relaxation becomes important as the ion concentration is increased, leading to the quenching of the 1460-nm band and enhancement of the 1860-nm emission. The highest emission cross section of 6.85×10^?21 cm² measured for the 1860-nm band reveals the potential of this host for the development of 2-μm lasers in bulk glass as well as fiber media.     

Study of electrical conductivity and phase transition in Bi2O3–V2O5 system

The solid solutions of bismuth–vanadate were prepared by the conventional solid-state reaction. The sample characterization and the study of phase transition were done by using FT-IR, X-ray diffraction (XRD) and DSC measurements. AC impedance measurements proved that the oxide ion conductivity predominantly arises from the grain and grain boundary contributions as two well-defined semicircles are clearly seen along with an inclined spike. The electrical conductivity of Bi₂O₃–V₂O₅ has been studied at different temperatures for various molar ratios. The isothermal conductivity increases with an increase in the concentration of V₂O₅ due to the vacancy migration phenomenon. It has been found that the conductivity of different compositions of Bi₂O₃–V₂O₅ increases and shows a jump in the temperature range 230–260°C due to the phase transition of BiVO₄ from monoclinic scheelite type to that of tetragonal scheelite type. The endothermic peak in DSC at around 260°C reveals the phase transition, which is also confirmed by the XRD and FT-IR analysis. The XRD patterns confirmed the monoclinic structure of BiVO₄.     

Asymmetric orientational writing dependence on polarization and direction in Li2O–Nb2O5–SiO2 glass with femtosecond laser irradiation

Strong birefringence photo-induced by the femtosecond laser irradiation and a sensitivity to the orientation of the laser movement versus the laboratory reference (i.e., difference between rightward and leftward or between upward and downward) have been demonstrated in 32.5Li₂O–27.5Nb₂O₅–40SiO₂ glass. An asymmetry with the orientation of the laser scanning was firstly observed by one of the authors in 2003 in pure silica (Poumellec et al. in Opt Express 11:1070, 2003). Here, we show in addition that this asymmetric orientational sensitivity is dependent on the direction of laser polarization and the laser scanning (i.e., when the direction is horizontal or vertical). In particular, no asymmetric writing is detected when both laser scanning and polarization directions are vertical. These observations are not explained by the available model.