Properties of high nitrogen content mixed alkali earth oxynitride glasses (AExCa1−x)1.2(1)SiO1.9(1)N0.86(6), AE = Mg,Sr, Ba

Mixed alkali earth element containing high nitrogen content oxynitride glasses (Ca_1?xAE_x)_1.2(1)SiO_1.9(1)N_0.86(6), with AE = Mg, Sr, Ba, x ≤ 0.30 for Mg and x ≤ 0.46 for Sr and Ba, and nominally constant (Ca/AE):Si:O:N ratios were prepared in order to investigate the compositional dependencies of physical properties on alkali earth element composition. The glasses were prepared by melting mixtures of AEH₂, CaH₂, SiO₂ and Si₃N₄ powders in nitrogen atmosphere at 1600–1700 °C and characterized by X-ray powder diffraction and scanning and transmission electron microscopy. Cation and anion glass compositions were determined by respectively energy dispersive X-ray analysis and combustion analysis. The determined physical properties were density, glass transition temperature, Vickers hardness, and refractive index. The physical properties were found to vary linearly with the degree of substitution of Ca by the AE elements. The density of the glasses increases substantially upon substitution by Sr and Ba, up to 3.99 g/cm³. Glass transition temperatures are found to be higher for Mg and Sr substituted glasses, ca. 900 °C, in comparison with Ba substituted glasses, ca. 850 °C. The hardness increases upon substitution by Mg, up to 12.2 GPa at x = 0.46, and decreases upon substitution by Sr and Ba. The refractive index increases upon substitution by Sr and Ba, up to 1.97 for Ba at x = 0.46, and decreases upon substitution by Mg. The transparency of the glasses was found to increase upon increasing substitution by Mg and completely transparent glasses were obtained for x = 0.24.     

Structural analysis of xCsCl(1 − x)Ga2S3 glasses

Sulphide glasses doped with rare-earth ions have been demonstrated to be suitable for photonic applications such as optical amplifiers, up-converters and fiber lasers. The substitution of metal halides into the glass network has been shown to result glasses with desirable properties in terms of quantum efficiency and fiber manufacture [J.R. Hector, J. Wang, D. Brady, M. Kluth, D.W. Hewak, W.S. Brocklesby, D.N. Payne, Journal of Non-Crystalline Solids 239 (1998) 176]. To assist in the understanding of this improvement a structural analysis of glasses with a composition xCsCl(1 ? x)Ga₂S₃ has been undertaken in order to examine the nature of the gallium environment. Information collected by high energy X-ray diffraction and neutron diffraction have been analyzed to permit the identification of the structural units as Ga centered tetrahedra. The interconnection between the tetrahedra was found to be predominantly corner sharing.     

Structural behavior of CuxZr100−x metallic glass (x = 35−70)

The structural behavior of rapidly quenched amorphous Cu_xZr_100?x alloys was investigated in a wide composition range between 35 and 70 at.% Cu content. High-energy X-ray diffraction patterns, atomic pair correlation functions, mass density and the thermal stability behavior of the alloys all exhibit monotonic changes with composition. Partial pair correlation functions were determined assuming that they remain unchanged in the different amorphous Cu_xZr_100?x alloys and only the weight fractions become altered with changes in composition. The experimental results can be well described by a solid solution-like replacement of Cu and Zr atoms in the whole composition range. No indications are observed neither for the existence of a special atomic arrangement at a particular chemical composition nor for the presence of phase separation in the glassy state of the binary Cu–Zr system.     

Enhanced 2.0 μm emission in oxyfluoride glass-ceramics containing nanocrystals MF2 (MF3): Ho3+,Tm3+ (M = Ca,Ba, and La)

Transparent glass-ceramics containing MF₂(MF₃):Ho³⁺,Tm³⁺ (M = Ca, Ba, and La) nanocrystals have been prepared by melt quenching and subsequent thermal treatment. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of MF₂ (MF₃) nanocrystals among the glass matrix. Energy-dispersive X-ray spectroscopy results evidenced the incorporation of Tm³⁺ and Ho³⁺ into the MF₂ nanocrystals. Intense 2.0 μm emission originating from the Ho³⁺: ⁵I₇ → ⁵I₈ transition was achieved upon excitation with 808 nm laser diode. A large ratio of the forward Tm³⁺ → Ho³⁺ energy transfer constant to that of the backward process indicated high efficient energy transfer from Tm³⁺ (³F₄) to Ho³⁺ (⁵I₇), and benefited from the reduced ionic distances of Tm³⁺–Tm³⁺ and Tm³⁺–Ho³⁺ pairs and low phonon energy environment with the incorporation of rare earth ions into the precipitated MF₂ nanocrystals. The results indicate that oxyfluoride glass-ceramic is a promising candidate for 2.0 μm laser.     

Microstructural analysis of Ga2S3–2MCl (M = K, Rb, Cs) glasses using Raman scattering

Raman scattering spectra of Ga₂S₃–2MCl (M = K, Rb, Cs) glasses have been conducted at room temperature. Based on the analysis of the local co-ordination surroundings of Cs⁺ ions, the similarities and differences of Raman spectra for the glass Ga₂S₃–2CsCl and the bridged molecular GaCl₃ were explained successfully. Through considering the effect of M⁺ ions on mixed anion units [GaS_4?xCl_x] and bridged units [Ga₂S_6?xCl_x] and the corresponding microstructural model, the Raman spectral evolution of the Ga₂S₃–2MCl (M = K, Rb, Cs) glasses was reasonably elucidated.     

Amorphous Ni59Nb40PtxM1−x (M = Ru, Sn) electrocatalysts for oxygen reduction reaction

The oxygen reduction reaction, ORR, on amorphous Ni₅₉Nb₄₀Pt₁, Ni₅₉Nb₄₀Pt_0.6Ru_0.4 and Ni₅₉Nb₄₀Pt_0.6Sn_0.4 electrocatalysts was analyzed by electrochemical techniques such as cyclic voltammetry, CV; rotating disk, RDE, and ring-disk electrodes, RRDE, in a 0.5 M H₂SO₄ solution. The reduced amount of platinum and the incorporation of transition metals in the amorphous catalysts were found to have significant effect on the kinetic parameters of the cathodic reaction. The kinetics study (RRDE) performed on the amorphous catalysts showed a high activity towards the ORR, preferentially proceeding via multi-electron (4e^?) charge transfer pathway toward water formation, with less than 2.8% H₂O₂ in the region of PEMFC applications. The performance on Ni₅₉Nb₄₀Pt₁ was different, which may be related to changes in the electrode surface enrichment of one or two of the amorphous alloy constituents. The performance towards the cathodic reaction allows to envisage that incorporation of small amounts of Pt in the catalyst, may lead to the fabrication of good amorphous electrocatalytic materials with possible applications as cathode electrodes in polymer electrolyte fuel cells.     

Structural characterization and phase transformation kinetics of Se58Ge42−xPbx (x = 9, 12) chalcogenide glasses

The glass transition behavior and crystallization kinetics of Se₅₈Ge_42?xPb_x (x = 9, 12) have been investigated using Differential Scanning Calorimetry (DSC) at five different heating rates under non-isothermal conditions. It has been observed that these glassy systems exhibit single glass transition and double crystallization on heating. The XRD pattern revealed that the considered glasses get crystallized into GeSe₂ and PbSe/Se phases after annealing at 633–643 K for 2 h. The GeSe₂ and Se phases were found to crystallize in monoclinic structure while, PbSe phase crystallizes in cubic structure. Besides this, a mixed phase was also observed in DSC thermograms after annealing. The kinetic studies include determination of various parameters such as Avrami exponent (n), frequency factor (K_o), dimensionality of growth (m), the activation energy for glass transition (E_t) and for crystallization (E_c). The values of E_t increases while that of E_c decreases after annealing. Also, dimensionality of growth decreases to one dimension from two and three dimensions after annealing.     

Synthesis and structure–property relations in xCuO–(1 − x)Bi2O3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the xCuO–(1 ? x)Bi₂O₃ (0.5 ? x ? 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ～0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g-matrix elements g_|| > g_⊥ > g_e for the glasses C1–C5 at 4.2 K are due to the Cu²⁺ (3d⁹) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O_1/2–CuO_4/2–O_1/2] having D_4h symmetry. IR spectroscopic results show the presence of octahedron [BiO_6/2]^3? and [CuO_6/2]^4? units and pyramidal [BiO_2/2O]^? unit in the glasses.     

Nanostructured Crystals of Fluorite Phases Sr1 – xRxF2 + x (R Are Rare-Earth Elements) and Their Ordering. 14: Concentration Dependence of the Defect Structure of Nonstoichiometric Phases Sr1 – xNdxF2 + x As Grown (x = 0.10, 0.25, 0.40, 0.50)

Crystallography Reports - The defect structure of as grown Sr1 – xNdxF2 + x (x = 0.10–0.50) crystals grown from a melt by...     

Growth and characterization of lead-free Ba(1−x)CaxTi(1−y)ZryO3 single crystal

A lead-free Ba_(1?x)Ca_xTi_(1?y)Zr_yO₃ (BCZT) single crystal (x=0.08, y=0.26) was grown by the Czochralski (CZ) method in a mixed flux of TiO₂ and ZrO₂. The composition of as-grown BCZT was analyzed by electron probe micro-analysis. The structure, dielectric properties and phase transition were investigated at different temperatures. The X-ray diffraction results confirmed that the structure of the as-grown BCZT crystal was cubic both at 25 °C and 500 °C. The temperature dependence of the dielectric constant and Raman spectra characterization revealed that there was a phase transition from cubic to tetragonal, which happened between 200 K and 250 K. With increasing frequency, the Curie temperature shifted towards high temperature.     

Specific effects of nanometer scale size on magnetic ordering in La1−xCaxMnO3 (x = 0.1, 0.3 and 0.6) manganites

To check the impact of nano-size originated effects on the magnetic ordering in doped manganites, X-band electron magnetic resonance measurements were performed on nanometer sized and bulk samples of La_1?xCa_xMnO₃ (x = 0.1, 0.3 and 0.6). The model fittings of EPR signal parameters and complementary magnetic measurements indicate that bulk La_0.9Ca_0.1MnO₃ shows inhomogeneous confinement of charge carriers, leading to its mixed magnetic ordering. The carriers mobility within impurity-like band and ferromagnetic (FM)-like ground state are observed on nanocrystals of the same composition. The bulk La_0.7Ca_0.3MnO₃ demonstrates homogeneous FM order and band-like carrier mobility. The surface magnetic disorder in its nano-counterpart leads to appearance of two magnetic phases – a core phase (bulk-like in properties) and a surface phase with notably reduced temperature of magnetic ordering; neither double-exchange interaction nor carriers mobility exist between these phases. The size reduction induced effects in La_0.4Ca_0.6MnO₃ are: an increase of surface FM-like component and a decrease of the charge-ordering temperature. These findings allow us to conclude that the nano-scale effect on magnetic ordering in La_1?xCa_xMnO₃ system weakens progressively upon stabilization of the low temperature magnetic ground state with Ca-doping.     

Production and properties of high purity TeO2− WO3−(La2O3, Bi2O3) and TeO2− ZnO−Na2O−Bi2O3 glasses

TeO₂–WO₃ (TW), TeO₂–WO₃–La₂O₃ (TWL), TeO₂–WO₃–La₂O₃–Bi₂O₃ (TWLB) and TeO₂–ZnO–Na₂O–Bi₂O₃ (TZNB) glasses were produced by high-purity oxide mixtures melting in platinum or gold crucible at 800 °C in the atmosphere of purified oxygen. The total content of Cu, Mn, Fe, Co and Ni impurities was not more than 0.1–0.5 ppm wt in the initial oxides and glasses. The stability of TZNB glasses to crystallization, characterized by (T_x ? T_g) value more than 150 °C, was demonstrated by DSC measurements at heating rate 10 K/min. In the case of La₂O₃-containing glasses the thermal effects of both crystallization and fusion of the crystallized phases were not observed. The hydroxyl groups absorption coefficients of pure tellurite glasses at the maximum of the absorption band (λ ~ 3 μm) were in the region of 0.012–0.001 cm^?1. The optical absorption losses, measured by the laser calorimetry method at λ = 1.56 and 1.97 μm, did not exceed 100 dB/km.     

Nanostructured Crystals of Fluorite Phases Sr1 – xRxF2 + x (R Are Rare-Earth Elements) and Their Ordering. 13: Crystal Structure of SrF2 and Concentration Dependence of the Defect Structure of Nonstoichiometric Phase Sr1 – xLaxF2 + x As Grown (x = 0.11, 0.20, 0.32, 0.37, 0.47)

Crystallography Reports - The defect structure of as-grown SrF2 and nonstoichiometric phases Sr1 – xLaxF2 + x (x = 0.11, 0.20, 0.32, 0.37, 0.47) single...     

Nanostructured Crystals of Fluorite Phases Sr1 – xRxF2 + x (R Are Rare-Earth Elements) and Their Ordering. 15. Concentration Dependence of the Defect Structure of As Grown Nonstoichiometric Phases Sr1 – xRxF2 + x (R = Sm,Gd)

Crystallography Reports - The defect structure of as grown single crystals Sr1 – xSmxF2 + x (x = 0.14, 0.26) and...     

Luminescence of Dy3+-doped GexGa5Se(95−x) glasses

Dysprosium doped Ge_xGa₅Se_(95?x) (x = 15–30) chalcogenide glasses were synthesized in this present work. The Vis–NIR transmission spectra, photoluminescence spectra and lifetime were measured. Glasses (x = 27.5, 29.17 and 30) doped with 0.2 wt% dysprosium ions shows relatively strong emission bands at 1146 and 1343 nm when pumped at 808 nm. The emission lifetime ranged from 440 to 540 μs. The oscillator strengths and intensity parameters Ω_t (t = 2, 4 and 6) were calculated using Judd–Ofelt theory.     

Magnetic, magnetocaloric, and lattice properties of the La(Fe x Si1 − x )13 ferromagnets

The magnetic and lattice properties of a sample of La(Fe_0.86Si_0.14)₁₃ ferromagnet have been measured. The influence that neutron irradiation has on the physical properties of this ferromagnet is studied. It is shown that the irradiation of this sample by a fluence of 3 × 10¹⁹ n/cm² increases the lattice constant a and the Curie temperature (T _C ) as the volume magnetostriction decreases. A model of ferromagnet is proposed which satisfactorily describes the dependence a(T) of the initial and irradiated samples and their magnetic properties. The temperature dependence of the change in entropy when switching the magnetic field on and off is calculated. It is established that the change in both the magnetic and lattice parts of the total entropy at the magnetic phase transition must be taken into account for La(Fe _x Si_{1 ? x} )₁₃ compounds.     

Influence of Temperature on the Defect Structure of the Fluorite Sr1 – xLaxF2 + x (x = 0.11–0.33) Single Crystals

Crystallography Reports - X-ray diffraction data on the Sr1 – xLaxF2 + x (x = 0.11, 0.24, 0.32, 0.33) single crystals with different thermal histories...     

Crystallization behavior of Ce70−xAl10Cu20Cox (x = 0, 1, 3, 5 at.%) amorphous alloys

The effect of Co addition (substituting for Ce) on crystallization behavior of Ce₇₀Al₁₀Cu₂₀ amorphous alloys has been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The Co addition has an obvious effect on topological short-range ordering of Ce–Al–Cu–(Co) amorphous alloys. Moreover, the Co addition can slightly improve the thermal stability of Ce–Al–Cu based amorphous alloys. The 1 and 3 at.% Co additions do not obviously change the crystallization behavior of the Ce–Al–Cu–(Co) amorphous alloys, and the final crystallization products are FCC–CeAlCu(Co)O. However, the 5 at.% Co addition can alter the crystallization behavior of the Ce₇₀Al₁₀Cu₂₀ amorphous alloys. Proper content of Co can effectively suppress the formation of oxide phases during annealing of the Ce–Al–Cu–(Co) amorphous alloys.