Distribution of species in Na2O–CaO–B2O3 glasses as probed by FTIR

The article presents a simple method that can be used to get the concentration of various species in mixed-modifier borate glasses. By using the fraction of four coordinated boron in xCaO (30 − x)Na₂O70B₂O₃ (0 ≤ x ≤ 27.5 mol%) and xCaO(40 − x)Na₂O60B₂O₃ glasses (10 ≤ x ≤ 40 mol%), the concentration of BO₄⁻ and asymmetric BO₃ units related to each modifier oxide could be determined. CaO has a greater tendency to form asymmetric BO₃ units in the first glass series, while Na₂O has the ability to form BO₄ units to a greater extent. In xCaO(40 − x)Na₂O60B₂O₃ glasses, BO₄⁻ and asymmetric BO₃ units are formed at the same rate from Na₂O and CaO. The fraction of four coordinated boron, can be predicted by treating the studied glasses as if they are mixtures of Na₂O–B₂O₃ and CaO–B₂O₃ matrices. The change in N₄ is due to change in the relative concentration of these matrices.     

Infrared,Raman and XPS spectroscopic studies of Bi2O3–B2O3–GeO2 glasses

Glasses with composition 50Bi₂O₃–(50 ? x) B₂O₃–xGeO₂ (x = 0, 5, 10, 15 mol%) were prepared by conventional melting method. The thermal properties were investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of GeO₂. The glass transition temperature (T_g), onset crystallization temperature (T_x) and ΔT (T_x ? T_g) increase as well. The cut-off edges in ultraviolet and infrared shift to longer wavelength by the addition of GeO₂. Infrared, Raman and XPS results indicate that the glass network consists of [Bi–O₆] octahedron, [BO₃] triangle, [BO₄] tetrahedron and [GeO₄] tetrahedron and borate oxide mainly exists in [BO₃] units. XPS result indicates Ge⁴⁺ ions form steady [GeO₄] tetrahedra units in the glass network and the number of non-bridging oxygens decreases with the addition of GeO₂.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Gamma ray induced changes on vibrational spectroscopic properties of strontium alumino-borosilicate glasses

The present investigation reports the effect of influence of aluminum ions on radiation damage of strontium borosilicate glasses studied by means of spectroscopic (viz., optical absorption (OA), infrared and Raman spectra). The composition of the glasses chosen for the study is 40SrO–xAl₂O₃–(15-x) B₂O₃–40SiO₂ (x = 5, 7.5, 10), all in mol%. The glasses were synthesized by conventional melt quenching method. Later, the samples were exposed to gamma (γ) radiation dose of strengths 10 kGy and 30 kGy with a dose rate of 1.5 Gy/s using ⁶⁰Co as radiation source. The infrared spectra (IR), Raman spectra and optical absorption (OA) spectra of the samples were recorded at ambient temperature before and after irradiation. The OA spectra of the pre-irradiated samples do not exhibit any absorption bands in the UV–vis regions and IR and Raman spectra exhibited conventional vibrational bands due to different borate, silicate AlO₄ and AlO₆ structural units. The OA spectra of post irradiated samples exhibited a broad absorption band in the wavelength region 600–750 nm; it is attributed to electron trapped color centers. The intensity of this peak is observed to increase with increase of the γ-ray dose. Considerable changes in the intensities of various bands in the IR and Raman spectra were also observed. The changes were explained based on structural modifications taking place in the glass network due to γ-ray irradiation and finally it is concluded that the glasses mixed with 10.0 mol% of Al₂O₃ are relatively more radiation resistant.     

Structural properties of silver nanoclusters–phosphate glass composites

The structure of the xAg₂O(100 − x)[50P₂O₅·30CaO·20Na₂O] glasses, with x = 0, 3 and 5 mol%, was investigated by means of Raman and infrared spectroscopy. The structural changes induced by the Ag₂O presence into the soda-calcium–phosphate matrix were evidenced and discussed in terms of the network depolymerization process and distortion of the PO₄ tetrahedra. The existence of silver nanoclusters inside the glass matrix, considered to be mainly responsible for the found structural behavior, was supposed by results obtained from the analysis of the UV–vis absorption spectra and further proved by transmission electron microscopy images.     

Structural investigation and electron paramagnetic resonance of vanadyl doped alkali niobium borate glasses

Glasses with compositions xNb₂O₅·(30 ? x)M₂O·69B₂O₃ (where M = Li, Na, K; x = 0, 4, 8 mol%) doped with 1 mol% V₂O₅ have been prepared using normal melt quench technique. The IR transmission spectra of the glasses have been studied over the range 400–4000 cm^?1. The changes caused by the addition of Nb₂O₅ on the structure of these glasses have been reported. The electron paramagnetic resonance spectra of VO²⁺ ions in these glasses have been recorded in X-band (9.14 GHz) at room temperature (300 K). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V⁴⁺ ions which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glasses. The tetragonality of V⁴⁺O₆ complex decreases with increasing concentration of Nb₂O₅. The 3d_xy orbit contracts with increase in Nb₂O₅:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported.     

Spectroscopic properties of RBiBO4 (R = Ca,Sr) glasses doped with TiO2

Transparent glasses, melt quenching derived, containing 10RO·20Bi₂O₃·(70 ? x)B₂O₃·xTiO₂ [R = Ca, Sr] with x = 0, 0.5, 1.0 wt% were characterized by X-ray powder diffraction. Physical and spectroscopic properties viz., density, absorption, emission, electron paramagnetic resonance (EPR) and FTIR were investigated. The absorption band around 823 nm in pure glass samples is attributed to the electronic transition of ³P₀ to ³P₂ of Bi⁺ radicals. A small absorption hump centered around 609 nm is found in all doped glasses due to ²T_2g to ²E_g transition of octahedral Ti³⁺ ions. The emission results revealed that all the samples exhibit a broad emission band covering entire visible-light range, with λ_ex = 360 nm, centered 470–520 nm corresponds to electronic transition of ³P₁ to ¹S₀ of Bi³⁺ ions, therefore the present materials can be potentially used as tunable or full-color display systems. And a strong emission around 706 nm with λ_ex = 514 nm due to transition of ²P_3/2 to ²P_1/2 of Bi²⁺ ions. In SrO mixed glasses Ti⁴⁺ ions effect the environment of Bi³⁺ ion symmetry units from C₂ to C_3i. A small EPR signal (at room temperature) is observed in titanium doped glasses due to Ti³⁺ ions. In both the series with increase of TiO₂ concentration BO₄ units are gradually converted into BO₃ units and new cross linkages are formed, like B–O–Ti, Bi–O–Ti at the expense of B–O–B bonds.     

Dual role of the six-coordinated molybdenum and lead ions in novel of photochromic properties of the molybdenum–lead–borate glasses

Transparent glasses were prepared by conventional melting–quenching method in the xMoO₃·(100 ? x)[3B₂O₃·PbO] system where 0 ≤ x ≤ 15 mol%. By increasing the MoO₃ content up to 20 mol% the PbMoO₄ crystalline phase appears. These systems exhibit a photochromic effect which can be induced through laser exposures (λ = 633 nm) directly on the bulk sample. Structural investigations by FTIR spectroscopy show that the photosensitive effect is due to a reduction of Mo⁶⁺ to Mo⁴⁺ and/or Mo⁵⁺ promoted by the oxidation of Pb²⁺ and some structural changes of the borate network.     

Optical absorption and near infrared emission properties of Nd3+ ions in alkali lead tellurofluoroborate glasses

Nd³⁺ doped H₃BO₃–PbO–TeO₂–RF (R = Li, Na and K) glasses were prepared through melt quenching technique. Optical absorption and near infrared (NIR) fluorescence spectra were recorded at room temperature. The spectral intensities were analyzed in terms of the Judd–Ofelt (J–O) parameters (Ω_λ = 2, 4, 6). The covalency effect of Nd–O bond on the J–O parameters was estimated from the relative absorbance ratio (R) between ⁴I_9/2 → ⁴F_7/2 and ⁴I_9/2 → ⁴S_3/2 transitions. The effect of Nd–O covalency on the Ω₄ and Ω₆ intensity parameters as well as on the spontaneous emission probabilities (A_R) was discussed. Lomheim and Shazer hybrid method was applied to determine the fluorescence branching ratios (β_R) of each emission transition from the ⁴F_3/2 metastable level to its lower lying levels. The evaluated total radiative transition probabilities (A_T), stimulated emission cross-sections (σ_e) and gain bandwidth parameters (σ_e × Δλ_P) were compared with the earlier reports.     

Thermal,IR, Raman characteristics,Raman gain coefficient and bandwidths in quaternary glasses

Tellurite glasses with composition 75TeO₂–5WO₃–15Nb₂O₅–5M_xO_y in mol%, where M_xO_y = (Na₂O, Ag₂O, ZnO, MgO, CuO, NiO, TiO₂, MnO₂) have been prepared by using the conventional melt-quenching method. Thermal characteristic of prepared glasses were investigated by using DTA techniques. It was found that the glass with the composition 751TeO₂–5WO₃–15Nb₂O₅–5TiO₂ had high thermal stability (ΔT = 122 °C at heating rate 15 K/min). Raman gain coefficients and bandwidths of prepared glasses for Raman gain media were evaluated. The glass with composition 75TeO₂–5WO₃–15Nb₂O₅–5Na₂O had the maximum value of Raman gain coefficient (g = 4.43 × 10⁻¹² m/W) and it was 24 times as large as silica glass. The highest value of full width half maximum (FWHM ≈ 185 cm⁻¹) was observed in glass system 75TeO₂–5WO₃–15Nb₂O₅–5NiO. Finally, the structure of the glasses was investigated through deconvolution Raman and IR spectra.     

Infrared,Raman and XPS spectroscopic studies of Bi2O3–B2O3–Ga2O3 glasses

Glasses with compositions 60Bi₂O₃–(40?x)B₂O₃–xGa₂O₃ (x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga₂O₃. The glass transition temperature (T_g), the onset crystallization temperature (T_x), ΔT (T_x?T_g) decrease with the content of Ga₂O₃. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga₂O₃. On the other hand, the addition of Ga₂O₃ causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi⁵⁺ and Bi³⁺ exist in 5 mol% Ga₂O₃ content, while Bi⁵⁺ amounts decrease with the increase of Ga₂O₃ contents. The glass is mainly composed of [BiO₆], [BO₃], [BO₄] and [GaO₄] polyhedra. Glasses are supposed to have layer structure. [BO₃] triangle and [BO₄] tetrahedra may be located between the [GaO₄] tetrahedral and [BiO₆] octahedra to prevent crystallization and to compensate electric charge.     

Mechanochemical synthesis and ionic conductivity of lanthanum phosphosilicate oxyapatites

Lanthanum phosphosilicate apatites with the chemical formula Sr_10–xLa_x(PO₄)_6–x(SiO₄)_xO, where 0 ≤ x ≤ 6, usually prepared by a solid-state reaction at about 1400 °C, were synthesized via the mechanochemical method at room temperature. The samples were characterized using powder X-ray diffraction, infrared spectroscopy and thermal analysis. The results showed that the prepared products were carbonated apatites and no secondary phase was detected. The realization of the milling under a controlled atmosphere can lead to oxyapatites containing no carbonates. The ionic conductivity of the Sr₆La₄(PO₄)₂(SiO₄)₄O sample was investigated by using impedance spectroscopy. The highest ionic conductivity value of 1.522 × 10⁻⁶ S·cm⁻¹ was found at 800 °C. In the investigated temperature range, the activation energy is of 0.85 eV.     

Hopping conductivity of distorted K2NiF4-type (Ca1+xNd1−x)CrO4

Orthorhombic distorted K₂NiF₄-type (Ca_1+xNd_1?x)CrO₄ (0.00 ≤ x ≤ 0.15) was synthesized using a standard ceramic technique. The cell parameters (a and c) decreased, whereas the cell parameter (b) increased with the increase in x. The variation in the global instability index (GII) indicated that the crystal stability of (Ca_1+xNd_1?x)CrO₄ was not influenced by the Cr⁴⁺ ion content. At all temperatures, the electrical conductivity (σ) of (Ca_1+xNd_1?x)CrO₄ increased with the increase in x. (Ca_1+xNd_1?x)CrO₄ was a p-type semiconductor and exhibited hopping conductivity in a small-polaron model in the temperature range of 290 K ≤ T ≤ 713 K. The Cr⁴⁺ ion acts as an acceptor, and the electron transfer through the Cr³⁺–O–Cr⁴⁺ path becomes active as a result of the Cr⁴⁺ ion content and the Cr–O(1) distance.     

Spectroscopic investigation and magnetic properties of Na2Pb1−xCuxP2O7 glasses

Phosphate glasses have several technological interests due to their specific physical properties such as high thermal expansion coefficient, high refractive indice and low melting temperature, that make them suitable for use as conductors, ionic conductors, semiconductors and biomedical materials. The phosphate glasses, in particular the pyrophosphate forms, are not widely studied. In this work we have elaborated the Na₂Pb_1−xCu_xP₂O₇ glasses, with a large range of composition (0 ≤ x ≤ 1), by conventional melting method. Thermal parameters of the glasses were determined using the differential scanning calorimetry. The structure of the glasses was investigated by IR spectroscopy. The local environment of paramagnetic ions Cu²⁺ was analyzed by EPR and magnetic measurements. It was showed that the network structure of the glasses was drastically influenced by the copper content.     

Crystal structure and phase transitions of sodium potassium niobate perovskites

This paper presents the crystal structure and the phase transitions of K_xNa_1?xNbO₃ (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100–800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic–tetragonal and tetragonal–cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.     

Chimie douce preparation of CuxZn3−xV2O7(OH)2·yH2O isostructural to trigonal zinc pyrovanadate

New Cu_xZn_3−xV₂O₇(OH)₂·yH₂O (0 < x ≤ 1.5) isostructural to zinc pyrovanadate Zn₃V₂O₇(OH)₂·2H₂O, were successfully prepared by using a chimie douce technique. The method consists in mixing zinc nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V₂O₅ with few millilitres of 30 vol.% H₂O₂ followed by addition of distilled water). When ammonium hydroxide NH₄OH 10% was added (pH ≈ 6), a precipitate was obtained. Using powder X-ray diffraction data, the crystal structures of as-prepared samples were determined by Rietveld refinement. Copper substitutes zinc in the zinc pyrovanadate lattice and is found to introduce distortion in the structure, which is mainly due to the Jahn–Teller effect. Distortion becomes more pronounced when the amount of copper is increased. This restricts the amount of copper which can be incorporated in the hexagonal zinc pyrovanadate lattice.     

Comments on stabilizing layered manganese oxide electrodes for Li batteries

An electrochemical study of structurally-integrated xLi₂MnO₃•(1 −x)LiMn_0.5Ni_0.5O₂ ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li₂MnO₃-rich end of the Li₂MnO₃–LiMn_0.5Ni_0.5O₂ tie-line, i.e., for 0.7 ≤ x ≤ 0.95. Excellent performance was observed for x = 0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content (x ≥ 0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed.     

Controllable thermal expansion and phase transition in Yb2−xCrxMo3O12

The thermal expansion and phase transition of solid solutions Yb_2?xCr_xMo₃O₁₂ have been investigated by X-ray powder diffraction and differential thermal analysis. The XRD patterns and the results of Rietveld refinement of Yb_2?xCr_xMo₃O₁₂ indicate that the solid solution limit was in the composition range of 0.0 ≤ x ≤ 0.4 and 1.7 ≤ x ≤ 2.0. Yb_2?xCr_xMo₃O₁₂ (0.0 ≤ x ≤ 0.4) has an orthorhombic structure and exhibits negative thermal expansion between 200 °C and 800 °C. Yb_2?xCr_xMo₃O₁₂ (1.7 ≤ x ≤ 2.0) crystallizes in monoclinic below the phase transition and above, transforms to orthorhombic. Both monoclinic and orthorhombic compounds Yb_2?xCr_xMo₃O₁₂ (1.7 ≤ x ≤ 2.0) present positive thermal expansion. Orthorhombic Yb_2?xCr_xMo₃O₁₂ exhibit anisotropic thermal expansion with the contraction of a and c axes, and the linear thermal expansion coefficients range from negative to positive with increasing chromium content. Partial substitution of Yb³⁺ for Cr³⁺ exhibits depressed monoclinic to orthorhombic phase transition.     

Structural and optical properties of sprayed Zn1−xMnxO films

In recent years the dilute magnetic semiconductors have received much attention due to the complementary properties of semiconductor and ferromagnetic behaviour. Zn_1−xMn_xO thin films have been synthesized by chemical spray pyrolysis at a substrate temperature of 400 °C with different manganese compositions that vary in the range, 0.0 ≤ x ≤ 0.25, on Corning 7059 glass substrates. The X-ray diffraction studies revealed that all the films were strongly oriented along the (002) orientation corresponding to the hexagonal wurtzite structure. The crystalline quality of the layers was found to decrease with the increase of x, however, no structural changes were observed over the ‘Mn’ composition range investigated. The optical absorption studies revealed that the energy band gap of the films followed the Vegard's law. The optical band gap of the films prepared at x = 0.15 was found to be ∼3.35 eV. The photoluminescence characteristics of Zn_1−xMn_xO films showed an emission peak at around 390 nm with a broad band about 530 nm. The details of these results were reported and discussed.     

The local structure of bismuth germanate glasses and glass ceramics doped with europium ions evidenced by FT-IR spectroscopy

Glasses of the xEu₂O₃·(100 − x)[4Bi₂O₃·GeO₂] system, with 0 ≤ x ≤ 30 mol%, have been characterized by FT-IR spectroscopy measurements in order to obtain information about the influence of Eu₂O₃ on the local structure of the 4Bi₂O₃·GeO₂ glass matrix. FT-IR spectroscopy data suggest that the europium ions play the network modifier role in the studied glasses and both Bi₂O₃ and GeO₂ play the role of network formers. Melting at 1100 °C and the rapid cooling at room temperature permitted to obtain glass samples. In order to improve the local order and to develop crystalline phases the glass samples were kept at 700 °C for 17 h. Both the influences of the europium ions as well as of the heat treatment on the local order of 4Bi₂O₃·GeO₂ glass matrix have been discussed.