Solid-state NMR study of bioactive binary borosilicate glasses

A series of binary borosilicate glasses prepared by the sol-gel method are shown to be bioactive. Tetraethyl orthosilicate (TEOS) and trimethylborate (TMB) in acidic medium are used to prepare xB₂O₃·(1−x)SiO₂ glass systems for x=0.045-0.167. The formation of a layer of apatite-like mineral on the glass surface becomes apparent after soaking in simulated body fluid for 48 h. We have measured the ¹¹B-¹¹B homonuclear second moments of the borosilicate glasses and inferred that no macroscopic phase separation occurred in our glasses. The ¹¹B chemical shift data also show that the formation of clustered boroxol rings is negligible in our glass system. Although the bioactivity of our borosilicate glasses is less than that of CaO-SiO₂ sol-gel glasses, these simple binary systems could be taken as reference glass systems for the search of new bioactive borosilicate glasses.     

Compositional dependence of the optical properties of novel Ge-Ga-Te-CsI far infrared transmitting chalcohalide glasses system

A systematic series of (Ge₁₅Ga₁₀Te₇₅)_1−x(CsI)_x (x=0, 5, 10, 15 at%) far infrared transmitting chalcohalide glasses were prepared by the traditional melt-quenching method. The physical, thermal and optical properties were determined. The allowed direct transition and indirect transition of samples were calculated according to the Tauc equation. The results show that glass transition temperatures (T_g) were in the range 133-175 °C, with ΔT values between 81 and 130 °C. The highest values of metallization criterion (0.244) and energy gap (1.191 eV) were obtained for (Ge₁₅Ga₁₀Te₇₅)₈₅(CsI)₁₅. When the dissolved amount of CsI increased from 0 to 15 at%, the direct optical band gap and indirect optical band gap were in the ranges 0.629-1.075 eV and 0.438-0.524 eV, respectively. The Ge-Ga-Te-CsI glasses have an effective transmission window between 1.7 and 25 μm, encompassing the region of interest for bio-sensing applications.     

Optical properties of samarium doped zinc-phosphate glasses

Samarium doped zinc-phosphate glasses having composition Sm₂O_{3 (x)}ZnO_(60−x) P₂O_{5 (40)} (where x=0.1-0.5 mol%) were prepared by melt quenching method. The density of these glasses was measured by Archimedes method; the corresponding molar volumes have also been calculated. The values of density range from 3.34 to 3.87 gm/cm³ and those of molar volume range from 27.62 to 31.80 cm⁻³. The optical absorbance studies were carried out on these glasses to measure their energy band gaps. The absorption spectra of these glasses were recorded in UV-visible region. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range of 2.89-4.20 eV. The refractive index and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. The values of refractive index range from 2.13 to 2.42 and those of polarizability of oxide ion range from 6.51×10⁻²⁴ to 7.80×10⁻²⁴ cm³.     

Effect of Bi2O3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi₂O₃·(30−x)M₂O·70B₂O₃ (M=Li, Na) containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤15 (x is in mol%). The electron paramagnetic resonance spectra of VO²⁺ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g_∥, g_⊥, A_∥, A_⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra. In xBi₂O₃·(30−x)Li₂O·70B₂O₃ glasses there is decrease in the tetragonality of the V⁴⁺O₆ complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi₂O₃·(30−x)Na₂O·70B₂O₃ glasses there is increase in the tetragonality of the V⁴⁺O₆ complex with increasing x. The 3d_xy orbit expands with increase in Bi₂O₃:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10⁻⁵ ohm⁻¹ m⁻¹ at low temperature and 10⁻³ ohm⁻¹ m⁻¹ at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi₂O₃:M₂O ratio.     

Modification of dielectric relaxations in sodium bismuth titanate with samarium doping

Na_0.5Bi_(0.5−x) Sm_xTiO₃ (NBST) ceramics with x=0.05, 0.1, and 0.15 are prepared through chemical route. The X-ray diffraction studies confirmed the formation of single phase. Dielectric measurements in the temperature region ranging from room temperature (∼30 °C) to 600 °C at different frequencies (10 kHz-1 MHz) showed anomalies at 130, 306, and 474 °C (at 10 kHz frequency) for x=0.05 sample. Other samples showed only two peaks. To establish the electrical nature of these relaxations, impedance measurements are done at different temperatures and frequencies. The relaxation time, obtained from both impedance and modulus data, is found to decrease with increase in temperature. The relaxations observed are of non-Debye type. Increase in samarium content increases the activation energy for relaxation.     

Second-harmonic generation in the thermal/electrical poling (100−x)GeS2·x(0.5Ga2S3·0.5CdS) chalcogenide glasses

Utilizing Maker fringe (MF) method, second-harmonic generation (SHG) has been observed within the GeS₂-Ga₂S₃-CdS pseudo-ternary glasses through thermal/electrical poling technique. The SHG phenomenon was considered to be the result of breakage of the glassy macroscopic isotropy originated from the reorientations of dipoles during the thermal/electrical poling process. Under the same poling condition conducted with 5 kV and 280 °C for 30 min, the maximum value of second-order nonlinear susceptibility χ⁽²⁾ of the poled (100−x)GeS₂·x(0.5Ga₂S₃·0.5CdS) glasses was obtained to be ≈4.36 pm/V when the value of x is equal to 30. Nonlinear dependence of χ⁽²⁾ on compositions of these glasses can be well explained according to the theory related to the reorientation of dipoles.     

Physicochemical, structural and fluorescence properties of Er-doped Ge-S-Ga glasses

Erbium-doped (GeS₂)_x(Ga₂S₃)_100−x (x=75, 80, 85, 90 mol%) glasses have been characterized by some basic parameters, which are important from a practical point of view. The influence of Er by introduction of 0.3, 0.6, and 0.9 mol% Er₂S₃ on the properties has been studied. The glasses have relatively high glass transition temperatures and high thermal stability, the maximal being at x=80 (the difference between the crystallization and glass transition temperatures has been found to be 150 °C. The values of Vickers microhardness and density increase with increasing GeS₂ content, slightly depending on the presence of the Er³⁺ ions. The distribution and changes of the structural units, caused by addition of Ga₂S₃ and Er₂S₃ to GeS₂, have been specified by the Raman scattering in the range 50-550 cm⁻¹. The intensity dependence of the luminescence on glass composition has been evaluated. The glasses have shown a good chemical durability and their resistance to the moisture is relatively high. The obtained results have supported possible applications of these glasses in rare-earth doped devices.     

Reversibility window in as-quenched Ge-As-S glasses

Thermoanalytical characteristics and Raman scattering of high purity sulfur and ternary bulk glasses Ge_xAs_xS_(100−2x) for x=4-22 at. % were studied. The intermediate phase characterized by vanishing of non-reversing heat flow ΔH_nr, i.e. so-called the thermally reversing window was found between mean coordination number 〈r〉∼2.28-2.47. Separated phase of non-crystalline cycloocta-S, manifesting itself by λ-transition at ∼155 °C, was found for glasses with sulfur content higher than ∼80 at.%. Raman spectra of studied Ge-As-S glasses showed different shapes in three different areas according to three distinct phases of network glasses-floppy, intermediate, rigid.     

Effect of composition and thermal annealing on the absorption and electrical conduction of Se85−xTe15Sbx glasses

The optical absorption of the as-prepared and thermally annealed Se_85−xTe₁₅Sb_x (0≤x≤9) thin films was measured. The mechanism of the optical absorption follows the rule of non-direct transition. The optical energy gap (E₀) decreased from 1.12 to 0.84 eV with increasing Sb content of the as-prepared films from 0 to 9 at.%. The as-prepared Se₇₆Te₁₅Sb₉ films showed an increase in (E₀) with increasing the temperature of annealing in the range above T_g (363 K). The electrical conductivity of the as-prepared and annealed films was found to be of Arrhenius type with temperature in the range 300-360 K. The activation energy for conduction was found to decrease with increasing both the Sb content and temperature of annealing. The results were discussed on the basis of the lone-pair electron effect and of amorphous crystalline transformation.     

Optical and electronic polarizability investigation of Nd-doped soda-lime silicate glasses

This paper reports on different physical and optical properties of Nd³⁺-doped soda-lime silicate glass. The glasses containing Nd³⁺ in (65−x)SiO₂:25Na₂O:10CaO:xNd₂O₃ (where x=0.0-5.0 mol%) have been prepared by the melt-quenching method. In order to understand the role of Nd₂O₃ in these glasses the density, molar volume, refractive index and optical absorption were investigated. The results show that the density and molar volume of the glasses increase with an increase in Nd₂O₃ concentration and consequently generate more non-bridging oxygen (NBOs) into glass matrix. The optical absorption spectra were measured in the wavelength range from 300 to 700 nm and the optical band gaps were determined. It was found that the optical band gap decreases with an increase in Nd₂O₃ concentration. On the basis of the measured values of density and refractive index, the Nd³⁺ ion concentration in glasses, the polarizability of oxide ions and optical basicity were theoretically determined.     

Effects of protons and acceptor substitution on the electrical conductivity of La6WO12

Transport properties and non-stoichiometry of La_1−xCa_xW_1/6O₂ and La_1−yW_1/6O₂ (x=0, 0.005, 0.05; y=0.05, 0.1) have been characterized by means of impedance spectroscopy, the EMF-technique, H⁺/D⁺ isotope exchange, and thermogravimetry in the temperature range 300-1200 °C as a function of oxygen partial pressure and water vapor partial pressure. The materials exhibit mixed ionic and electronic conductivities; n- and p-type electronic conduction predominate at high temperatures under reducing and oxidizing conditions, respectively. Protons are the major ionic charge carrier under wet conditions and predominates the conductivity below ∼750 °C. The maximum in proton conductivity is observed for LaW_1/6O₂ with values reaching 3×10⁻³ S/cm at approximately 800 °C. The high proton conductivity for the undoped material is explained by assuming interaction between water vapor and intrinsic (anti-Frenkel) oxygen vacancies.     

Fluorophosphate glasses containing manganese

New fluorophosphate glasses based on MnF₂, NaPO₃ and MF_n (M=Zn²⁺, Sr²⁺, Mg²⁺, Ba²⁺, Li⁺, Na⁺ and K⁺) have been synthesised and characterized. Large vitreous areas were observed. Samples of 4 mm in thickness have been obtained. These glasses are easy to prepare and stable in ambient air. Depending on the composition and the nature of the M cation, glass transition temperature, T_g, lies between 230 and 314 °C, crystallisation temperature, T_x is between 320 and 475 °C. These glasses are pink coloured, and infrared transmission extends up to 4.5 μm with extrinsic OH⁻ absorption band at 3200 cm⁻¹ and other bands around 2200 and 1600 cm⁻¹ that relate to PO₄ tetrahedron vibration. Other physical properties including density, microhardness, Young modulus, thermal expansion and refractive index were investigated and correlated to composition.     

The influence of microscopic parameters on the ionic conductivity of SrBi2(Nb1−xVx)2O9−δ(0≤x≤0.3) ceramics

Layered SrBi₂(Nb_1−xV_x)₂O_9−δ (SBVN) ceramics with x lying in the range 0-0.3 (30 mol%) were fabricated by the conventional sintering technique. The microstructural studies confirmed the truncating effect of V₂O₅ on the abnormal platy growth of SBN grains. The electrical conductivity studies were centred in the 573-823 K as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D₀) and the mean free path (a) were calculated by using Rice and Roth formalism. The conductivity parameters such as ion-hopping rate (ω_p) and the charge carrier concentration (K′) term have been calculated using Almond and West formalism. The aforementioned microscopic parameters were found to be V₂O₅ content dependent on SrBi₂(Nb_1−xV_x)₂O_9−δ ceramics.     

Phase- and shape-controlled synthesis of cadmium hydroxyl chloride microstructures via an ammonia-assisted conversion of 1D CdQCl (Q=quinoline) complex microwires

In this paper we reported a NH₃·H₂O-assisted solvothermal route for successful synthesis of cadmium hydroxyl chlorides (Cd_x(OH)_yCl_z) microstructures with different phases and shapes, employing 1D CdQCl (Q=quinoline) complex microwires as the precursor. Experiments contained two processes: firstly, CdQCl complex microwires with 500–600 nm in diameter and several hundreds of micrometers in length were prepared by the complexation between CdCl₂·2.5H₂O and quinoline at room temperature; then, CdQCl microwires were solvothermally treated at 150 °C for 10 h in the presences of different amounts of NH₃·H₂O to produce Cd_x(OH)_yCl_z microstructures with various phases and shapes. The as-obtained precursor and Cd_x(OH)_yCl_z microstructures were characterized by scanning electron microscopy, transmission electron microscopy, Infrared spectrometry and X-ray powder diffraction. Experiments showed that hexagonal Cd(OH)Cl was obtained from water–methanol system, while rhombohedral Cd₄(OH)₅Cl₃ from methanol system. Also, it was found that the shapes of Cd_x(OH)_yCl_z could be tuned by the amounts of NH₃·H₂O. Furthermore, the UV diffuse reflection and photoluminescence spectra of the precursor and Cd_x(OH)_yCl_z were also investigated.     

Structure and elastic properties of TeO2-BaF2 glasses

Binary tellurite (100−x)TeO₂-xBaF₂ glasses for different compositions of BaF₂ (x=8, 10, 12, 15, 18 and 20 wt%) have been prepared by rapid quenching method. The velocities and attenuation during the propagation of the ultrasonic waves in all glasses were measured using a transducer operated at a fundamental frequency of 5 MHz at room temperature. A progressive increase in BaF₂ content leads to a decrease in ultrasonic velocities and density, which is followed by an increase in attenuation. The existence of depolymerisation of Te co-ordination leads to the transformation of TeO₄ trigonal bipyramid units through TeO₃₊₁ polyhedron to TeO₃ trigonal pyramid units. This is responsible for the observed decrease in the measured and determined parameters with the addition of the modifier content.     

Preparation, structure and oxide ion conductivity in Ce6−xYxMoO15−δ (x=0.1-1.4) solid solutions

The Ce_6−xY_xMoO_15−δ solid solution with fluorite-related structure have been characterized by differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), IR, Raman, scanning electric microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The electric conductivity of samples is investigated by Ac impedance spectroscopy. An essentially pure oxide-ion conductivity of the oxygen-deficiency was observed in pure argon, oxygen and air. The highest oxygen-ion conductivity was found in Ce_5.5Y_0.5MoO_15−δ ranging from 5.9×10⁻⁵ (S cm⁻¹) at 300 °C to 1.3×10⁻² (S cm⁻¹) at 650 °C, respectively. The oxide-ion conductivities remained stable over 80 h-long test at 800 °C. These properties suggested that significant oxide-ionic conductivity exists in these materials at moderately elevated temperatures.     

Magnetic, electric, and optical functionalities of (PLZT)x(BiFeO3)1−x ferroelectric-ferromagnetic thin films

We have prepared a series of (PLZT)_x(BiFeO₃)_1−x transparent thin films with thickness of 300 nm by a thermal pyrolysis method. Only films with x≦0.10 formed a single phase of perovskite structure. The film where x=0.10 exhibited both ferromagnetic and ferroelectric properties at room temperature with spontaneous magnetization and coercive magnetic fields of 0.0027μ_B and 5500 G, respectively. The remanent electric polarization and coercive electric field for the film where x=0.10 were 3.0 μC/cm² and 24 kV/cm, respectively. Additionally, films with 0.02≦x≦0.10 showed both magneto-optical effects and the second harmonic generation of transmitted light.     

Some studies about the green and red light emitting structures in NaCl1−xBrx:Mn

In this work we present the results obtained from the luminescence spectra and X-ray diffraction as well as transmission electron microscopy, at room temperature on crystals of NaCl_1−xNaBr_x:MnCl₂:0.3% (x=0.00, 0.05, 0.25, and 0.50). The results suggest the existence of structures between the crystal planes (1 1 1) and (2 0 0), which may be associated with different types of Mn²⁺ arrangements, such as dipole complexes, octahedral and rhombohedral structures as well as other possible nanostructures that include mixtures of bromine/chlorine ions. These are responsible for the emission spectra of “as grown” crystals consisting of maxima around 500 nm and 600 nm. The green emission has been usually attributed to rhombohedral/tetrahedral symmetry sites; the present results point out that this is due to Mn–Cl/Br nanostructures with rhombohedral structure. On the other hand when the crystals are thermally quenched from 500 °C to room temperature the structures previously detected present changes. Only a red band appears around 620 nm if the samples are later annealed at 80 °C.     

Photocatalytic O2 evolution performances of Cd1+xIn2−2xSnxO4 (x=0.1, 0.3, 0.5, 0.7, 1.0) conducting oxides

The conducting oxides solid solutions of Cd_1+xIn_2−2xSn_xO₄ (x=0.1, 0.3, 0.5, 0.7, 1.0) were prepared via a solid state reaction method. The band gaps were estimated to be 2.4 eV for x=1.0, 2.5 eV for x=0.7, 2.6 eV for x=0.5, 2.7 eV for x=0.3 and 2.8 eV for x=0.1. Oxygen could be evolved over Cd₂SnO₄ under the irradiation of Xe-lamp or even visible light (λ>420 nm), while the others could only work in the UV-light range. Raman showed the cation distribution in Cd₂SnO₄ is ordered, while that in the others is disordered. The cations distribution was proposed to be the cause of the difference in photocatalytic O₂-evolution activities.     

Phase transformation behavior and dielectric characteristics of BaTi1−x(Al1/2Nb1/2)xO3 (0.01≤x≤0.40) ceramics

Microstructure, phase transformation behavior and dielectric properties of BaTi_1−x(Al_1/2Nb_1/2)_xO₃ (0.01≤x≤0.40) ceramics were investigated. A high level of (Al_1/2Nb_1/2)⁴⁺ substitution for Ti⁴⁺ ions was not conducive to the stability of the perovskite structure and resulted in the formation of BaAl₂O₄. As x was increased, lattice constants and unit cell volume decreased, reached a minimum at x=0.10 and then increased. The BaTi_1−x(Al_1/2Nb_1/2)_xO₃ ceramics at room temperature experienced a transformation from ferroelectric to paraelectric phase with increasing (Al_1/2Nb_1/2)⁴⁺ concentration. Meanwhile, permittivity of the BaTi_1−x(Al_1/2Nb_1/2)_xO₃ ceramics was markedly reduced, while Q value was slightly increased. Frequency dispersion of dielectric peak was obviously increased as x was increased from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200-400 K was observed for the composition with x=0.40.