Synthesis and Li ion conductivity of Li2O-Nb2O5-P2O5 glasses and glass-ceramics

Glasses with the compositions of xLi₂O-(70 − x)Nb₂O₅-30P₂O₅, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li⁺ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li⁺ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li₂O content, and the glass of 60Li₂O-10Nb₂O₅-30P₂O₅ shows the value of σ = 2.35 × 10⁻⁶ S/cm at room temperature and the activation energy (E_a) of 0.48 eV for Li⁺ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li₃PO₄ and NbPO₅ are formed in the crystallization of the glasses and the crystallization results in the decrease in Li⁺ ion conductivity in all samples, indicating that any high Li⁺ ion conducting crystalline phases have not been formed in the present glasses. 60Li₂O-10Nb₂O₅-30P₂O₅ glass shows a bulk nanocrystallization (Li₃PO₄ nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10⁻⁷ S/cm at room temperature and E_a = 0.49 eV.     

Influence of modifier oxides on some physical properties of antimony borate glass system doped with V2O5

Three series of glasses, of the composition 20 MO (M = Ca, Pb, Zn)–40 Sb₂O₃–(40 − x) B₂O₃:xV₂O₅, with six values of x ranging from 0 to 1 mol% were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy, EDS and differential scanning calorimetric techniques. The comparison of DSC data among the three series has indicated high glass forming ability for ZnO mixed glasses. Dielectric properties over a range of frequency and temperature, optical absorption, ESR spectra at room temperature and IR spectra have been investigated. The variations observed in all these properties due to different modifiers as a function of the concentration of V₂O₅ have been analyzed in the light of different oxidation states and environment of vanadyl ions in these glasses. The analysis of these results indicated that the ZnO mixed glasses are more stable against devetrification and possess high insulating strength when compared with PbO and CaO mixed glasses.     

Raman spectroscopic study of structure of WO3La2O3B2O3 glasses with no color and crystallization of LaBWO6

Glasses with the nominal compositions of xWO₃25La₂O₃(75 − x)B₂O₃ (mol%) with x = 15, 25, and 50 were prepared using a conventional melt quenching method, and their structure and crystallization behavior were examined from Raman scattering spectra and X-ray diffraction analyses. The glasses are colorless in the visible light region and give the optical band gap energy of 3.49-3.61 eV. The glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing WO₃ content. The strong Raman bands at 840 and 940-960 cm⁻¹ suggest that the main coordination state of W⁶⁺ ions in the glasses is isolated (WO₄)²⁻ tetrahedral units. The formation of WO₆ octahedral units is also suggested in the glasses with high WO₃ contents. The main crystallization mechanism in the glasses is the surface crystallization, and the glass of 50WO₃25La₂O₃25B₂O₃ shows the crystallization of LaBWO₆ single phase. The present study proposes that WO₃La₂O₃B₂O₃ glasses and crystallized glasses are very interesting as optical functional materials.     

Influence of mixed alkali on the spectral properties of vanadyl ions doped xNa2O-(30 − x)K2O-60B2O3 glasses—an EPR and optical study

Electron paramagnetic resonance (EPR) and optical investigations have been performed in the mixed alkali borate xNa₂O-(30 − x)K₂O-60B₂O₃ (5 ≤ x ≤ 25) glasses doped with 10 mol% of vanadyl ions in order to look for the effect of ‘mixed alkalis’ on the spectral properties of the glasses. The observed EPR spectra have structures for x > 5 mol% which are characteristic of a hyperfine interaction arising from an unpaired electron with the ⁵¹V nucleus and it builds up in intensity as x increases. It is observed that the mixed alkali play a significant role in accommodating the vanadyl ions in these mixed alkali glasses and for x > 5 mol%, shows a well resolved hyperfine structure typical for isolated VO²⁺ ions. The spin-Hamiltonian parameters (g and A), the dipolar hyperfine coupling parameter (P) and Fermi contact interaction parameter (k) have been evaluated. It is observed that the spin-Hamiltonian parameters do not vary much with the change in composition. It is observed that with increase of x, an increase occurs in tetragonal distortion for VO²⁺. The number of spins (N) participating in resonance and the paramagnetic susceptibility (χ) have been calculated. It is observed that N and χ increase with x. The optical bandgap energies evaluated for these glasses slightly increase with x and reach a maximum around x = 20 and thereafter decrease showing the mixed alkali effect. Optical band gap energies obtained in the present work vary from 2.73 to 3.10 eV for both the direct and indirect transitions. The physical parameters of the glasses are also determined with respect to the composition.     

The phase transformation and crystallization kinetics of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glasses

The phase transformation and crystallization kinetics of (1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses have been studied by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) analysis. The crystallization temperature at the exothermic peak increases from 1171 to 1212 K when the Na₂O content increases from 0 to 0.6 mol. The crystalline phase is composed of spodumene crystallization when the Na₂O content increases from 0 to 0.6 mol. The activation energy of spodumene crystallization decreases from 444.0 ± 22.2 to 284.0 ± 10.8 kJ mol⁻¹ when the Na₂O content increases from 0 to 0.4 mol. Moreover, the activation energy increases from 284.0 ± 10.8 to 446.0 ± 23.2 kJ mol⁻¹ when the Na₂O content increases from 0.4 to 0.6 mol. The crystallization parameters m and n approach 2, indicating that the surface nucleation and two-dimensional growth are dominant in (1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses.     

Effect of silver concentration on the silver-activated phosphate glass

The effects of silver concentration on the structure and properties of silver-activated phosphate glasses, with the nominal molar compositions xAg₂O·(1 − x)(30Na₂O·10Al₂O₃·60P₂O₅) and 0 ≤ x ≤ 10 mol%, were studied. Increasing the Ag₂O-content decreases the glass transition temperature (T_g), increases the thermal expansion coefficient (TEC) and increases the glass dissolution rate in water. ³¹P nuclear magnetic resonance (NMR) and Raman spectroscopies indicate that the addition of Ag₂O leads to the formation of chain-terminating P-tetrahedra, and ²⁷Al NMR spectra indicate that Al-octahedra are the preferred structural moiety. Optical spectroscopy indicates that Ag₂O-additions shift the UV-absorption edge to longer wavelengths. Irradiating glasses with ≤1.0 mol% Ag₂O with ⁶⁰Co γ-rays creates a photoluminescence (PL) center that emits near 605 nm when excited with UV light (337.1 nm). The intensity of this PL center is proportional to the radiation dosage (up to 200 Gy), and the relative sensitivity is maximized in glasses with 0.05 mol% Ag₂O. When x > 1 mol% Ag₂O, a second PL center, emitting at 470 nm, is activated. The formation of this second PL center is associated with the loss of radiation sensitivity for glasses with greater Ag₂O-contents.     

Sol-gel preparation and properties of TiO2-P2O5 bulk glasses

Monolithic transparent and colorless, or Ti³⁺-free TiO₂-P₂O₅ glasses containing very large amounts of TiO₂ (up to 93 mol%) were successfully prepared by heat-treating the xerogels, which were made from titanium tetraisopropoxide and triethyl phosphate, through the sol-gel reaction. The density and refractive index n_632.8 nm of the sol-gel-derived glasses were higher than the melt-derived glasses of the corresponding compositions. The glasses of TiO₂ content of larger than 80 mol% seemed somewhat porous, but n_632.8 nm of these glasses was very high as 2.2-2.3. Higher density and higher n_632.8 nm than the melt-derived glasses were considered to be due to more abundance of six-fold coordinated Ti⁴⁺ ions.     

Elastic properties and spectroscopic studies of fast ion conducting Li2OZnOB2O3 glass system

Glass systems of the composition xLi₂O-20ZnO-(80 − x)B₂O₃ where (x = 5, 10, 15, 20, 25 and 30 mol%) have been prepared by melt quenching technique. Elastic properties, ¹¹B MAS-NMR and IR spectroscopic studies have been employed to study the structure of Li₂O-ZnO-B₂O₃ glasses. Elastic properties have been investigated using sound velocity measurements at 10 MHz. Elastic moduli reveal trends in their compositional dependence. The bulk modulus and shear modulus increases monotonically with increase of BO₄ units, which increase the dimensionality of the network. ¹¹B MAS-NMR and IR spectra show characteristic features of borate network and compositional dependent trends as a function of Li₂O/ZnO concentration. The results are discussed in view of borate network and the dual structural role of Zn²⁺ ions. The results indicate that the Zn²⁺ are likely to occupy network-forming positions in this glass system.     

Order-disorder phase transitions and high-temperature oxide ion conductivity of Er2+xTi2−xO7−δ (x = 0, 0.096)

The Er_2+xTi_2−xO_7−δ (x = 0.096; 35.5 mol% Er₂O₃) solid solution and the stoichiometric pyrochlore-structured compound Er₂Ti₂O₇ (x = 0; 33.3 mol% Er₂O₃) are characterized by X-ray diffraction (phase analysis and Rietveld method), thermal analysis and optical spectroscopy. Both oxides were synthesized by thermal sintering of co-precipitated powders. The synthesis study was performed in the temperature range 650-1690 °C. The amorphous phase exists below 700 °C. The crystallization of the ordered pyrochlore phase (P) in the range 800-1000 °C is accompanied by oxygen release. The ordered pyrochlore phase (P) exists in the range 1000−1200 °C. Heat-treatment at T ≥ 1600 °C leads to the formation of an oxide ion-conducting phase with a distorted pyrochlore structure (P2) and an ionic conductivity of about 10⁻³ S/cm at 740 °C. Complex impedance spectra are used to separately assess the bulk and grain-boundary conductivity of the samples. At 700 °C and oxygen pressures above 10⁻¹⁰ Pa, the Er_2+xTi_2−xO_7−δ (x = 0, 0.096) samples are purely ionic conductors.     

Luminescent properties of Eu-activated (Sr1−z, Caz)(Al1−y, By)2O4 phosphors for UV LEDs

A series of (Sr_1−z, Ca_z)(Al_1−y, B_y)₂O₄:xEu²⁺ phosphors were synthesized by the sol–gel process and were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL) excitation and emission spectra. The experiment results revealed that the highest intensity of Sr(Al_1.98, B_0.02)O₄:Eu²⁺ phosphor with pure monoclinic SrAl₂O₄ was achieved by annealing at the temperature of 1200 °C and the Eu²⁺ content of 8 mol%. However, when the post-treatment temperature for Sr(Al_1.98, B_0.02)O₄: Eu²⁺ was over 1200 °C, the Sr₄Al₁₄O₂₅ phase appeared as a minor phase, inducing small blue-shift in the emission peak (520–509 nm). Doping higher content of B³⁺ (y = 0.02–0.40) into SrAl₂O₄:Eu²⁺ at 1200 °C resulted in the transformation of phase from SrAl₂O₄ to Sr₄Al₁₄O₂₅ as well as to SrB₂Al₂O₇, which made the emission intensity enhance and the emission shift to a much shorter wavelength region (λ_p = 467 nm). It was found that, instead of purely using Sr atoms, Ca atoms with content of 20–40% could induce the crystal structure of (Sr_1−z, Ca_z)(Al_1−y, B_y)₂O₄:xEu²⁺, which led to SrAl₂O₄ from monoclinic to hexagonal phase. As a result, SrAl₂O₄ solid solution was obtained and then SrAl₂O₄:Eu²⁺ to emit 518 nm green light. At higher Ca content (z > 40%), a new CaAl₂O₄ solid solution was formed and a blue emission of CaAl₂O₄:Eu²⁺ was obtained.     

Natural Fe3O4 nanoparticles embedded zinc–tellurite glasses: Polarizability and optical properties

Modifying the optical behavior of zinc–tellurite glass by embedding magnetic nanoparticles has implication in nanophotonics. A series of zinc–tellurite glasses containing natural Fe₃O₄ nanoparticles with composition (80 − x)TeO₂·xFe₃O₄·20ZnO (0 ≤ x ≤ 2) in mol% are synthesized by melt quenching method and their optical properties are investigated using FTIR and UV–vis–NIR spectroscopies. Lorentz–Lorenz relations are exploited to determine the refractive index, molar refraction and electronic polarizability. The sharp absorption peaks of FTIR spectra show a shift from 667 cm⁻¹ to 671 cm⁻¹ in the presence of nanoparticles that increase the non-bridging oxygen, confirmed by the intensity change of the TeO₃ peak at 752 cm⁻¹. A new peak around 461 cm⁻¹ is also observed which is attributed to the band characteristic of covalent Fe–O linkages. A decrease in the Urbach energy as much as 0.122 eV and the optical energy band gap with the increase of Fe₃O₄ concentration (0.5–1.0 mol%) is evidenced. Electronic polarizability of the glasses increases with increasing Fe₃O₄ nanoparticles concentration up to 1 mol%. Interestingly, the polarizability tends to decrease with the further increase of Fe₃O₄ concentration at 2 mol%. The role of magnetic nanoparticles in influencing the structural and optical behavior are examined and understood.     

Dielectric properties and substitution mechanism of samarium-doped Ba0.68Sr0.32TiO3 ceramics

Ba_0.68Sr_0.32TiO₃ ceramics of perovskite structure are prepared by solid state reaction method with addition of x mol% Sm₂O₃, and their dielectric properties are investigated. It is found that, integrating with the lattice parameters and tolerance factor t, there is an alternation of substitution preference of Sm³⁺ for the host cations in perovskite lattice. Owing to the replacement of Sm³⁺ ions for Ba²⁺ ions in the A site, T_c rises with the increase of Sm₂O₃ doping when the doping content is below 0.1 mol%; meanwhile, when the content is more than 0.1 mol%, Sm³⁺ ions tend to occupy the B-site, causing a drop of T_c. Owing to the modifications of Sm³⁺ doping, dielectric constant, dissipation factor and temperature stability of dissipation factor are influenced remarkably, making it a superior candidate for environment-friendly applications. Moreover, the creation of oxygen vacancies controls the dielectric constant when the addition is above 0.1 mol%, so the dielectric constant decreases with increasing of samarium.     

Microstructure and relaxor ferroelectric properties of Bi2O3-doped strontium barium niobate ceramics

(1 − x) Sr_0.4Ba_0.6Nb₂O₆–xBi₂O₃ (0.00 ≤ x ≤ 0.20) ceramics were prepared by conventional solid-state reaction method. The microstructure, dielectric properties and P–E hysteresis loops of ceramics were investigated via X-ray diffraction, scanning electron microscope (SEM), Agilent E4980A and modified Sawyer–Tower circuit, respectively. XRD results showed the obtained ceramics were of tungsten bronze structure, and second phase Sr_0.4Ba_0.6Bi₂Nb₂O₉ was detected at high doping concentration. SEM results showed suitable Bi₂O₃ addition could reduce the sintering temperature and assist the grain growth. The dielectric characteristics exhibited diffuse phase transition phenomena, which were verified by linear fitting of the modified Curie–Weiss law. Besides, the relaxor ferroelectric properties of ceramics followed the Vogel–Fulcher relationship well. The P–E hysteresis loops became slimmer with increasing the Bi₂O₃ addition, leading to a gradually decrease in both remnant polarization (P_r) and coercive field (E_c).     

Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

Synthesis,characterization and photoluminescence properties of (Gd1−x,Eux)2O2SO4 sub-microphosphors by homogeneous precipitation method

(Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors were synthesized by homogeneous precipitation method from commercially available Gd₂O₃, Eu₂O₃, H₂SO₄ and (NH₂)₂CO (urea) starting materials. Fourier transform infrared spectra show that the precursors with different molar ratios of (NH₂)₂CO to Gd₂(SO₄)₃ (the m value) are mostly composed of gadolinium hydroxyl, carbonate and sulfate groups with some crystal water. X-ray diffraction indicated that the precursor (m = 5) can be transformed into pure Gd₂O₂SO₄ phase after heat treated at 900 °C for 2 h in air. Field emission scanning electron microscope micrographs illustrate that the Gd₂O₂SO₄ phosphor particles (m = 5) are quasi-spherical in shape and well dispersed, with a mean particle size of about 300–500 nm. Photoluminescence spectroscopy reveals that the strongest emission peak for (Gd_1−x,Eu_x)₂O₂SO₄ sub-microphosphors is located at 618 nm under 270 nm light excitation, which corresponds to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 5 mol% and the concentration quenching mechanism is due to the electric dipole–dipole interaction. Decay study reveals that the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions fits with a mono exponential function.     

Assessment of glass-forming ability and the effect of La2O3 on crystallization mechanism of barium-lead-zinc phosphate glasses

Differential scanning calorimetry (DSC) was used in this work to study the effect of La₂O₃ addition on crystallization mechanism of barium-lead-zinc phosphate glasses. Bulk glasses from two different routes (using P₂O₅ and H₃PO₄ as starting materials) presented only one crystallization peak. An assessment of glass-forming ability (GFA) was performed from recent theory that is connected to glass stability (GS), and is also correlated to critical cooling rate, q_cr. Systems with high La₂O₃ content presented some of the highest GS values and estimated critical cooling rates (q_cr) lower than 0.079 K/s. For both routes were determined the activation enthalpies for crystallization, that were 126 ± 12 kJ/mol (for P₂O₅) and 110 ± 32 kJ/mol (for H₃PO₄). The calculated Avrami n parameters, based on exothermic crystallization peaks, were 3.50 ± 0.33 (for P₂O₅) and 3.09 ± 0.91 (for H₃PO₄), considering data from the lowest heating rate (5 K/min). These values suggest that the DSC peaks should be associated to volume crystallization, due to La₂O₃ influence, and crystallization did not change significantly using different routes.     

Structural characterization of 0.5PbMg1/3Nb2/3O3-0.5BaxPb(1−x)TiO3 powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg_1/3Nb_2/3)O₃-0.5(Ba_xPb_(1−x)TiO₃) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h.     

YAG laser-induced structural modification in transition metal ion containing 40K2O-40Nb2O5-20SiO2 glasses

Glasses with the compositions of 40K₂O-40Nb₂O₅-20SiO₂ (in mol%) containing different concentrations (0.01, 1 and 2 mol%) of NiO were prepared by a melt quenching technique. The glasses were irradiated with a continuous wave Nd:YAG laser with a wavelength of 1064 nm, and a metastable crystalline phase of KNbO₃ was obtained. In 2 mol% NiO-doped glass, lines with a width of ∼10 μm are successfully patterned by laser irradiations with a power of 0.9 W and a scanning speed of 15 μm/s. It is found from micro-Raman scattering spectra that the lines are composed of the metastable crystalline phase of KNbO₃. The crystallization mechanism in Nd:YAG laser-induced crystallization in the glasses is discussed in comparison with the usual crystallization in an electric furnace.     

Self-controlled growth of Fe3BO6 crystallites in shape of nanorods from iron-borate glass of small templates

Fe₃BO₆ can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe₃BO₆ growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B₂O₃ − xFe₂O₃, x = 40–50 mol%. B₂O₃ as a strong glass former co-bridges the Fe³⁺ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe³⁺ species in form of a compound Fe₃BO₆, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B₂O₃ layer (15–25 nm thickness) has grown on the Fe₃BO₆ of the nanorods in situ in a specific structure. XPS bands in the Fe³⁺, B³⁺ and O²⁻ species confer this model structure. A local BO₃ → BO₄ conversion has incurred in the boroxol (B₃O_4.5)_n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm⁻¹.     

Pressureless sintering of negative thermal expansion ZrW2O8/Zr2WP2O12 composites

Negative thermal expansion material ZrW₂O₈/Zr₂WP₂O₁₂ composite was prepared by liquid phase sintering. The apparent density of ZrW₂O₈ without any sintering additive was about 3.7 g/cm³, corresponding to about 73% of its theoretical density. However, the relative density of the samples, sintered with more than 5 mol% P₂O₅ was about 90%. The identified phases were mainly ZrW₂O₈ with small amounts of WO₃, ZrO₂ and Zr₂WP₂O₁₂ by XRD. The intensity of Zr₂WP₂O₁₂ peaks increased with increasing P₂O₅ content. It was surmised that the melting of ZrO₂-P₂O₅ resulted in liquid phase formation, which is then converted to Zr₂WP₂O₁₂ on the final stage of sintering. Therefore, Zr₂WP₂O₁₂ phase was observed at the gap between the ZrW₂O₈ grains and at the triple junctions. The ceramics sintered with 20 mol% P₂O₅ showed a negative thermal expansion coefficient of − 4.0 × 10^− 6 °C^− 1.