IR and ESR investigations on V2O5–P2O5–BaO glass system with opto-electronic potential

The changes observed in the IR and ESR spectra of the xV₂O₅(1 ? x)[0.8P₂O₅ ? 0.2BaO] glass system with 0 ≤ x ≤ 50 mol% show that vanadium oxide acts as a network modifier at low concentration (x ≤ 5 mol%) and as a network former for high content (x ≥ 10 mol%). Thus the IR bands belonging to the phosphate groups are strongly reduced except the specific bands of the short chain phosphate units due to the phosphate network depolymerization and the spectra are dominated by the vibrations characteristic for POP, POV and VOV linkages. At the same time the changes observed in the ESR spectra of these glasses are explained supposing the superposition of two signals, one with a well-resolved hyperfine structure typical for isolated V⁴⁺ ions and a broad line characteristic for clustered ions. The line width dependence versus V₂O₅ content shows that dipole–dipole interactions exist between vanadium ions until x = 5 mol% and the superexchange interactions prevail at high content (x > 10 mol%).     

Glasses in the SiOCN system produced by pyrolysis of polycyclic silazane/siloxane networks

In this work, polycyclic silazane/siloxane networks bearing SiO and SiN bonds were synthesized, via hydrosilylation reaction, from cyclotrisilazane, [CH₂CH(CH₃)SiNH]₃, and cyclotetrasiloxane, [CH₃(H)SiO]₄, with different SiH:Sivinyl molar ratios. The resulting polymers were pyrolyzed up to 1000 °C, in N₂ atmosphere, producing SiOCN glasses. The polymer-to-ceramic transformation was studied by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), and chemical analysis. The 1000–1500 °C, high temperature structural evolution was also studied using X-ray diffraction (XRD) and FTIR. The hydrosilylation reaction produced ethylenic bridge crosslinked polymeric precursors with good thermal stability. The SiOCN glasses obtained with ceramic yields higher than 80 wt% showed spectra absorptions of SiN, SiO, and SiC bonds in FTIR. The XRD patterns of the products obtained at 1500 °C displayed diffraction peaks characteristic of β-SiC and a broad halo centered at 22° (2θ), due to the amorphous silica phase. β-SiC diffraction peaks in the XRD patterns were more intense for the precursor richer in polysiloxane units, although absorptions of SiN, SiC, and SiO bonds were also observed in the FTIR spectra. Thus, the final materials were characterized as SiC/SiOCN composites in nano/amorphous phases.     

Metalorganic chemical vapor deposition of mesoporous SiTiOC nanostructured thin films

SiTiOC mesoporous thin films have been obtained by metalorganic chemical vapor deposition (MOCVD) using titanium iso-propoxide (TIP) and tetraethylorthosilicate (TEOS) as starting precursors. The influences of both carrier gas and deposition temperature on the properties of the produced films were extensively studied. The low-angle XRD analysis confirms that, all produced films under different conditions (gas type and temperature) have the mesoporous structure. However, the deposition temperature was found to be much effective in controlling both morphology and composition of the final films than the type of carrier gas. The morphology of the produced films was totally converted from spherical shape-like nanoparticles at 700 °C to lengthy at higher temperature of 1000 °C. The SEM-EDX investigations proved that the composition of the produced films was composed of SiTiOC structure system. The PL analysis has demonstrated along with FT-IR data that all the deposited films at various deposition parameters were composed mainly of SiO₂, SiOC, SiC, TiO₂ and TiOC bond structures and most probably nanocomposite SiTiOC system thin films.     

Preparation,crystallization behavior and magnetic properties of nanoparticles magnetic glass–ceramics in the systems Fe2O3 CoO MnO2, Fe2O3 NiO MoO3 and Fe2O3 CoO V2O5

Ferrimagnetic glass–ceramics were prepared in the systems Fe₂O₃ CoO MnO₂ (S1), Fe₂O₃ NiO MoO₃ (S2) and Fe₂O₃ CoO V₂O₅ (S3). Small amount of H₃BO₄ was added to make the melting process easier. The samples were characterized using DTA, XRD, TEM and EDX. Sequence of crystallization was studied by applying heat-treatment at 800 and 1000 °C for 4 h. CoFe₂O₄ with crystallite sizes of ≈ 14–20 nm was successfully prepared beside FeCoOBO₃ and Co₃BO₅ in S1. NiMoO₄, (FeNi₂)O₂(BO₃) and NiO with crystallite size ≈ 56–79 nm were crystallized in S2. CoFe₂O₄, FeCoOBO₃ and Co₃BO₅ with crystallite size ≈ 6–8 nm were crystallized in S3. Magnetic hysteresis cycles were analyzed with a maximum applied field of 20 kOe at room temperature. From the obtained hysteresis loops Ms records higher values for S1 and S3 and lower value for S2, while coercivity reach maximum for S2. The variable, magnetic, data range gives a wide range for different applications.     

Transparent K2OTiO2P2O5SiO2 monolithic gels and inorganic amorphous solids through incomplete hydrolysis

Sol–gel derived transparent glasses are of technological interest because of its precisely controlled composition for multicomponent glasses at low temperature processing. The present work demonstrates a new and simple methodology for preparing transparent multicomponent oxide gels by incomplete hydrolysis of alkoxides. Through this processing, a small quantity of organic agencies resulted from incomplete hydrolysis of alkoxides self-disperses in inorganic oxide network, and thus control the formation of the monolith gel free of cracks. Specially, K₂OTiO₂P₂O₅SiO₂ gel monoliths have been synthesized through this route. The gels transformed into transparent K₂OTiO₂P₂O₅SiO₂ inorganic amorphous solids after heat treatment above 450 °C. This approach could be applied to many other multicomponent oxides.     

First principles study of oxygen-deficient centers in pure and Ge-doped silica

Using ab initio calculations on 108 atoms pure- and Ge-doped (2.8 mol%) silica-based supercells, we performed a statistical study on the electronic structure and energetic contribution of neutral oxygen vacancies, also named Oxygen Deficient Centers (ODCs). All the 72 oxygen sites in the amorphous silica (a-SiO₂) cell were considered as possible candidates for the formation of the vacancies leading to study 72 different Si-ODCs (SiSi bond) and 144 Ge-ODCs (GeSi bond). The distributions of structural parameters and formation energies of the ODCs were evaluated through Density Functional Theory calculations. The obtained parameters showed a wide distribution that can be mainly associated with the differences in the local environments surrounding the point defects. We show that the formation energies of Si and Ge-ODCs generated from the same oxygen site of our supercell are correlated. Moreover, the local asymmetry around the SiGe or GeSi bond can also affect their formation energies, providing a strong evidence for the influence of short-range environment on the ODC generation efficiency.     

A composition dependent thermal behavior of GexSe35−xTe65 glasses

Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk Ge_xSe_35?xTe₆₅ glasses (17 ? x ? 25); it is found that the glasses with x ? 20 exhibit two crystallization exotherms (T_c1 & T_c2). On the other hand, those with x ? 20.5, show a single crystallization reaction upon heating. The exothermic reaction at T_c1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at T_c2 is associated with the additional crystallization of rhombohedral GeTe phase. The glass transition temperature of Ge_xSe_35?xTe₆₅ glasses is found to show a linear but not-steep increase, indicating a progressive, but a gradual increase in network connectivity with Ge addition. It is also found that T_c1 of Ge_xSe_35?xTe₆₅ glasses with x ? 20, increases progressively with Ge content and eventually merges with T_c2 at x ≈ 20.5 (〈r〉 = 2.41); this behavior has been understood on the basis of the reduction in TeTe bonds of lower energy and increase in GeTe bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the Ge_xSe_35?xTe₆₅ glasses.     

Electron paramagnetic resonance and thermal behavior of vanadyl-doped mixed alkali bismuth borate glasses

Glasses with composition 15 Li₂O15K₂O10Bi₂O₃(60 ? x) B₂O₃: xV₂O₅ where x = 1, 3, 5, 7, and 9 mol% are prepared by normal melt-quench technique. Characterization of the prepared samples is done using X-ray diffraction, density and differential scanning calorimetry. The density and molar volume are found to increase with increasing x whereas the glass transition temperature decreases. Electron paramagnetic resonance spectra of the prepared samples are recorded using EPR-spectrometer operating in the X-band frequency. The resonance spectra are well resolved for x ≥ 5 mol% and the intensity of the resonance peak is found to increase with increasing x. The values of spin-Hamiltonian parameters (SHP) and molecular orbital coefficients are evaluated. From the values of SHPs it is concluded that V⁴⁺ ions in the present glass system exist as vanadyl ions in octahedral co-ordination with tetragonal compression. It is observed that the SPHs depend slightly on the relative concentration of V₂O₅. Further, the theoretical optical basicity of the glasses has also been evaluated and it is observed that the changes in optical basicity values are in accordance with the changes in SHPs.     

Structural characterization of lanthanum aluminosilicate glasses by 29Si solid-state NMR

We investigate the network structures of LaSiAlO glasses by ²⁹Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR). Their compositions span most of the glass-forming region of the ternary La₂O₃Al₂O₃SiO₂ system at 1600 °C. The ²⁹Si NMR resonances narrow and become progressively deshielded when Al substitutes for Si in the network, as well as for increasing La-content of the glass, which leads to network depolymerization. We compare experimental and calculated center of gravities of the ²⁹Si NMR peaks, the latter generated from different simplified models for the distributions of Al and Si as well as bridging oxygen (BO) and non-bridging oxygen (NBO) atoms over the networks. The data do not permit accurate quantifications and may only be interpreted in limiting scenarios. However, they indicate that both distributions are essentially randomized, implying a clear deviation of the Al/Si ordering from that according to a Loewenstein Al-avoidance, coupled with a nearly uniform partitioning of the NBO atoms between Al and Si tetrahedra.     

On the structure of tungstate–tellurite glasses

A continuous network model of xWO₃–(1 − x)TeO₂ glasses is developed, based on quantum-chemical calculation and Raman spectra analysis, in order to relate the structural and vibrational properties with glass composition. The tungstate–tellurite glass network is shown to be formed mainly by structural units of three types, TeO₄ trigonal bipyramids, OTeO₂ trigonal pyramids, and WO₆ octahedra with OW double bonds. Most of the W atoms are found to be incorporated into single OWO₅ octahedra, with no more than several percents of these atoms occurring in 2[OWO₅] paired tungstate centers. The structural and vibrational properties of tungstate–tellurite glasses of several compositions are analyzed by application of the model and a novel interpretation of the Raman spectra is suggested.     

Correlation between the 2.7 eV and 4.3 eV photoluminescence bands in silica glass

Our previous studies have reported the excitation energy dependence of the 2.7 and 4.3 eV photoluminescence (PL) bands in oxygen deficient silica glass at low temperature (∼20 K). An oxygen vacancy (O₃SiSiO₃) was thought to be the origin of the two PL bands. In order to verify the origin of the 2.7 and 4.3 eV PL bands in silica glass, we measured the PL band of various thermally heat treated silica glasses. In the sample after heat treatment, we did not observe the 4.3 eV PL band, though we did observe the 2.7 eV PL band. These results suggest that these two PL bands do not have a common origin.     

Optical characterization of 316L stainless steel coated with sol–gel titania

In this work 316L stainless steel substrates were coated with sol–gel derived films by means of the dip-coating technique. Titanium isopropoxide and ethanol were used as chemical precursor and solvent, respectively. The dip-coating step was performed using withdrawal speeds of 6 mm/min, 30 mm/min, and 60 mm/min. Next, the samples were heat treated in air for 30 min at 100 °C, 300 °C, and 400 °C. The processed composites were examined by FTIR and UV–vis spectroscopies. We observed that the materials prepared in this work can exhibit a variety of colors depending on the heat treatment temperature, withdrawal speed, and precursor:solvent molar ratio used in their processing. It is an important finding since this behavior could lead to architectural application of these materials. We believe that the changes observed in the UV–vis spectra and the colors of these samples could be related to the variation of the coating thickness as the processing conditions were modified. FTIR tests revealed that the ratio between the intensities of features ascribed to hydroxyl groups and TiO bonds decreased as the heat treatment temperature was increased. On the other hand, the ratio between bands related to TiOTi and TiO bonds decreased when the heating temperature was raised from 100 °C to 300 °C.     

The effects of ZnCl2 and ErCl3 on the vibrational spectra and structure of tellurite glasses

A series of zinc tellurite glasses, containing up to 40 mol% ZnCl₂ and doped with 1–10 mol% ErCl₃, was prepared by melting and casting and their structure was analyzed by polarized Raman and variable incidence infrared reflection spectroscopies. Kramers–Kronig analysis of the infrared reflectivity led to the identification of the vibrational mode components. The Raman spectra are dominated by an intense, depolarized boson peak at ∼45 cm⁻¹ and a high frequency, polarized peak at ∼767 cm⁻¹. The introduction of ZnCl₂ and ErCl₃ modifiers led to a blue shift of the high frequency peak, while the intensity of the boson peak was found to increase continuously with the Er³⁺ content. It is shown that the erbium and zinc compounds both break TeOTe bonds, introducing non-bridging chlorine species, connected mostly to the zinc atoms.     

X-ray photoelectron spectroscopy studies on the bonding properties of oxygenated amorphous carbon nitride thin films synthesized by pulsed laser deposition at different substrate temperatures

Oxygenated amorphous carbon nitride thin films (a-CN_xO_y) were deposited by pulsed laser deposition of camphoric carbon (CC) target at various substrate temperatures (ST). The influence of ST on the bonding properties of a-CN_xO_y films was investigated. The nitrogen to carbon (N/C) atomic ratio and oxygen to carbon (O/C) atomic ratio, bonding state and microstructure of the deposited a-CN_xO_y films were characterized by X-ray photoelectron spectroscopy (XPS) and been confirmed using standard measurement techniques. The bonding states between the C and N, and C and O in the deposited films are found significantly influenced by the ST during deposition process. The N/C and O/C atomic ratio of the a-CN_xO_y films reached the maximum value at 400 °C. The XPS C 1s shows the bonding state of a-CN_xO_y films changes from diamond-like tetrahedral (sp³) carbon and carbon (C–C) bonding to graphite-like trihedral (sp²) CC bonding with the increase of ST. While, the XPS N 1s shows the sp³ C–N bonds increases with higher rates compared with sp² CN bonds up to 400 °C, after which it decreases with higher ST. The C–N bonding of C–N, CN and CN were observed in the deposited a-CN_xO_y films.     

FTIR and UV–VIS spectroscopy investigations on the structure of the europium–lead–tellurate glasses

Glasses in the xEu₂O₃·(100-x)[4TeO₂·PbO₂] system where 0 ≤ x ≤ 50 mol% have been prepared using the melt quenching method. The influence of europium ions on the structure of lead–tellurate glasses has been investigated using density measurements, FTIR and UV–VIS spectroscopy. Structural changes produced by increasing the rare earth concentration were followed.The europium and lead ions show a preference towards [TeO₃] structural units causing a deformation of the TeOTe linkages. Structural changes inferred by analyzing the band shapes of IR spectra revealed that the increase of the Eu^+ 3 content causes the intercalation of [EuO_n] entities in the [TeO₄] chain network. The excess of oxygen can be supported into the glass network by the formation of [PbO_n] and [EuO_n] structural units.The UV–VIS spectroscopy data show that europium ions enter the glass matrix in the Eu²⁺ and Eu³⁺ valence states, the last being predominant in the studied glasses. The Pb^+ 2 ions produce strong absorption in the ultraviolet domain.     

Structural characteristic of Na2OP2O5GeO2 glass systems

Phosphate glasses based on xNa₂O0.5P₂O₅(0.5−x)GeO₂ (0.0 ⩽ x ⩽ 0.5) mol%, were prepared and their structures were characterized by magic angle spinning (MAS) nuclear magnetic resonance (NMR), Raman and IR spectroscopy techniques. It was found that the phosphate network of these glasses is composed of middle (Q²) and branching (Q³) phosphate tetrahedra, whereas germanium part in the network is composed of three- or four-membered GeO₄ tetrahedral rings. It was also found that the germanium tetrahedral are randomly connected to either Q² or Q³ phosphate units in the network. The glass network, especially the Q² units can be modified by the presence of Na ions. This modification is primarily associated with the phosphate. It is found that these glasses behave as if they are formed from a solution of GeO₂ and sodium–phosphate glass with various GeO₄ units and the Q² and Q³ phosphate units randomly distributed in the network.     

Stability of E′ centers induced by 4.7 eV laser radiation in SiO2

The kinetics of E′ centers ( Si) induced by 4.7 eV pulsed laser irradiation in dry fused silica was investigated by in situ optical absorption spectroscopy. The stability of the defects, conditioned by reaction with mobile hydrogen of radiolytic origin, is discussed and compared to results of similar experiments performed on wet fused silica. A portion of E′ centers and hydrogen are most likely generated by laser-induced breaking of Si–H precursors, while an additional fraction of the paramagnetic centers arise from another formation mechanism. Both typologies of E′ centers participate in the reaction with H₂ leading to the post-irradiation decay of the defects. This annealing process is slowed down on decreasing temperature and is frozen at T = 200 K, consistently with the diffusion properties of H₂ in silica.     

Metastable phase formation in rapidly quenched Zr80Pt20 alloys: Linkage to oxygen

Melt spun Zr₈₀Pt₂₀ ribbons having oxygen contents ranging from <200 to ≈5000 mass ppm are shown to form various metastable phases during quenching. In the presence of sufficient oxygen, a big cube Zr₆Pt₃O phase forms, but this structure is de-stabilized towards an icosahedral quasicrystalline structure at lower oxygen levels. Further reduction of oxygen promotes increasingly stable ZrPt bonds, and a metastable β-Zr(Pt) structure is formed.     

Effect of lead oxide on optical properties of Dy3+ ions in PbO–H3BO3–TiO2–AlF3 glasses

The effect of lead oxide (PbO) on optical properties of Dy³⁺-doped PbO–H₃BO₃–TiO₂–AlF₃ (LBTAFDy) glasses is investigated. The LBTAFDy glasses were prepared with different PbO contents ranging from 30 to 60 mol%. The Judd–Ofelt intensity parameters (Ω_{λ = 2, 4, 6}) are obtained by the least square fit analysis. It is found that the Ω₂ parameter and yellow-to-blue intensity ratio (Y/B) of the Dy³⁺ emission depend on the PbO content in LBTAFDy glass. The structural asymmetry around the Dy³⁺ ion and the DyO covalency are responsible for the changes in Ω₂ parameter and Y/B ratio. The variation of decay time of ⁴F_9/2 emission level with the PbO content also supports the changes in structural asymmetry and DyO covalency in LBTAFDy glass.     

Growth of amorphous SiO2 nano-wires on pre-oxidized silicon substrate via chemical vapor deposition

Without an additional silicon source, amorphous SiO₂ nano-wires were grown on the pre-oxidized silicon substrate with the assistance of Ni-based catalyst under ambient pressure. The as-grown amorphous SiO₂ nano-wires were characterized by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and selected area diffraction. The micro-region chemical composition investigation on the as-grown amorphous SiO₂ nano-wires was carried out using X-ray energy dispersion spectroscopy (EDS) on the HRTEM. The present work focuses on the formation of atomic H on the surface of pure zinc powder by introducing moisture (N₂ + H₂O) into the furnace at high temperature. The growth mechanism has been discussed and attributed to the vapor–liquid–solid (VLS) mechanism instead of the adopted solid–liquid–solid (SLS) mechanism owing to the observed evidence of an etching reaction of atomic H at the SiO₂ buffer layer and/or that of H at the Si substrate to form a gaseous hydro-silicon radical (SiH_x) that is then transported to the growth sites. The intrinsic luminescent behavior of the amorphous SiO₂ nano-wires in the range of 350–430 nm was also reported and discussed. These results provide an alternative and simple procedure for nanostructures growth, which will be helpful to understand the growth mechanism of one dimensional SiO₂ nanostructures.