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.     

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.     

Magnetic behavior,transport properties and nanocrystallization of melt-spun YxCe50 − xCu42Al8 (0 ≤ x ≤ 50) amorphous system

Amorphous Y_xCe_50 ? xCu₄₂Al₈ (0 ≤ x ≤ 50) ribbons prepared by melt-spinning on the Cu wheel were subjected to X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and to the measurements of magnetization and resistivity in the temperature range from 1.7 to 300 K. Effective activation energies, characteristic crystallization temperatures and enthalpies of as-quenched alloys have been determined. Two stages of crystallization have been observed in most samples (except shallow effects in Ce₅₀Cu₄₂Al₈). The activation energies have been calculated from the Kissinger relation to be 247 ± 18 and 570 ± 56 kJ/mol for Y₂₅Ce₂₅Cu₄₂Al₈ and Y₅₀Cu₄₂Al₈, respectively. The absence of the endothermic effect for x = 50, usually associated with a glass transition, below the primary crystallization event, indicates the presence of dispersed polyamorphous packing with a wide range of local glass transitions. The magnetization versus temperature plot for Y₂₅Ce₂₅Cu₄₂Al₈ points to a magnetic ordering at temperatures considerably below 50 K. This observation has been confirmed by the temperature dependence of resistivity, which exhibits a singularity at the same temperature. Moreover, a negative temperature coefficient of resistivity, characteristic of disordered systems, was observed. The electrical resistivity in the Y₂₅Ce₂₅Cu₄₂Al₈ amorphous alloy is governed by the weak localization of electrons.     

Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se₈₀Te₂₀)_100 ? xAg_x (0 ≤ x ≤ 4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328 K) and in between glass transition temperature and crystallization temperature (343 K). Thin films annealed at 343 K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100 nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10^? 5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358 K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.     

Dependences of the crystallization behavior of Al–Ni–La amorphous alloys on La and Ni contents

Crystallization behaviors of Al–Ni–La amorphous alloys with a fixed Ni (La) content of 6 at.% were investigated by X-ray diffraction and differential scanning calorimeter when the La (Ni) content changes from 3 to 9 at.%. The results show that the thermal stability of the amorphous alloys monotonically increases with increasing the La (Ni) content. Glass transition only exists in the alloys with the La (Ni) content higher than 6 at.%. La plays a more significant role than Ni in promoting the glass-forming ability, improving the thermal stability, stabilizing the supercooled liquid region, depressing the precipitation of fcc-Al in the first crystallization process and increasing the apparent activation energy of the first reaction.     

Calorimetric study and Kissinger analysis of melt-spun DyMn6−xGe6−xFexAlx (1 ⩽ x ⩽ 2.5) alloys

Thermal properties of rapidly quenched alloys from the DyMn_6?xGe_6?xFe_xAl_x (1 ? x ? 2.5) series produced by melt-spinning have been investigated by differential scanning calorimetry (DSC). The DSC curves show two exothermic effects connected with crystallization processes. Crystallization temperatures and enthalpies ΔH have been estimated. The systematic changes in these parameters allow concluding that the crystallization exothermic events are independent. Effective activation energies E have been determined using the Kissinger analysis and relatively high values up to 480 ± 20 kJ/mol for DyMn₄Ge₄Fe₂Al₂ have been found indicating high thermal stability of the amorphous state in this alloy series.     

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.     

Optical properties of amorphous (As0.33S0.67)100−xTex (x = 0, 1, 5 and 10) chalcogenide thin films,photodoped step-by-step with silver

We have analysed in detail the effect of silver-content on the optical properties of Ag-photodoped amorphous (As_0.33S_0.67)_100?xTe_x (with x = 0, 1, 5 and 10 at.%) chalcogenide thin films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of composition Ag_y[(As_0.33S_0.67)_100?xTe_x]_100?y, with y ? 18 at.%, were successfully obtained by successively photodissolving about 20- or 40-nm-thick layers of silver. The optical constants (n, k) have been accurately determined by an improved envelope method [J.M. González-Leal, R. Prieto-Alcón, J.A. Angel, D.A. Minkov, E. Márquez, Appl. Opt. 41 (2002) 7300], based on the two envelope curves of the optical-transmission spectrum, obtained at normal incidence. The dispersion of the refractive index of the Ag-photodoped chalcogenide films is analysed in terms of the Wemple–DiDomenico single-effective-oscillator model: $n^2(?\omega )=1-E_{\text{o}}{E}_{\text{d}}/(E_{\text{o}}^2-(?\omega {)}^2)$, where E_o is the single-oscillator energy, and E_d the dispersion energy. We found that the refractive index of the Ag-doped samples strongly increases with the Ag-content, whereas the optical band gap, $E_{\text{g}}^{\text{opt}}$, decreases also notably. For instance, in the particular case of x = 10 at.%, the largest Te-content, $E_{\text{g}}^{\text{opt}}$ decreases from 2.17 down to 1.67 eV. It should also be mentioned that, in the case of the undoped samples, when the Te-concentration increases from zero up to 10 at.%, the value of $E_{\text{g}}^{\text{opt}}$ decreases from 2.49 down to 2.17 eV.     

Phase transformations in the La1−xNdxNi3.5Al1.5–H2 (x = 0.1 and 0.2) system

Interactions in the La_1?xNd_xNi_3.5Al_1.5-Н₂ (x = 0.1 and 0.2) system was studied from room temperature up to 950 °C at the initial hydrogen pressure of 5 MPa through differential thermal (DTA) and X-ray phase analyses. Heating two-phase alloys (x = 0.1 and 0.2) in hydrogen results in their disproportionation (at 530 and 560 °С, respectively) and the formation of NiAl and unidentified amorphous products. The single-phase La_0.9Nd_0.1Ni_3.5Al_1.5 alloy decomposes in hydrogen at 900 °С into a hydride of rare-earth metals and an Ni₃Al intermetallic; traces of NiAl and hydride of a phase of the CaCu₅-type structure have also been observed. Heating the disproportionated samples in vacuum to 520–550 °С leads to their recombination into a homogenized phase with a CaCu₅-type structure. In other words, the increase of neodymium content shifts the reaction equilibrium of La_1?xNd_xNi_3.5Al_1.5 alloys with hydrogen towards recombination.     

Crystallization kinetics of a-Se75Te25 − xGax (x = 0, 5, 10 and 15 at wt %) glassy system

Bulk glasses of a-Se₇₅Te_25 ? xGa_x (x = 0, 5, 10 and 15 at wt %) have been prepared by melt quenching technique. These samples were structurally characterized by using X-ray diffraction. Kinetic of crystallization in these glasses was studied under non-isothermal conditions using differential thermal analysis (DTA). DTA is performed at different heating rates of 5, 10, 15, 20 and 30 °C/min. The values of glass transition (T_g) and crystallization peak temperature (T_p) are found to be composition and heating-rate dependent. The obtained results have been analyzed in terms of activation energy of glass transition (E_g) using Kissinger's and Mahadevan et al. relations. Values of E_g obtained by the two relations are in agreement with each other. The results indicate that the crystallization process is a three-dimensional growth.     

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.     

The internal friction and elastic modulus of amorphous Pd–Si and Fe–P–C alloys

The internal friction and the shear modulus of the amorphous Pd₈₀–Si₂₀–, Fe₈₀–P₁₃–C₇ and Fe₅₀–Ni₃₃–P₁₂–C₅ alloys have been measured at about 0.5 Hz over a temperature range from room temperature to about 550°C. The internal friction rises steeply with temperature and shows maxima around the crystallization temperature. The activation energy for the steeply rising internal friction has been estimated by the two different procedures; from the shift of the curve by the frequency change and from the slope of the In Q^?1 versus 1/T plot. The two values are very different, which indicates the existence of a wide distribution of activation energies. Crystallization of the amorphous alloys resulted in an increase of about 30% in the shear modulus.     

Growth of Sm1 – ySryF3 – y (0 < y ≤ 0.31) Crystals and Investigation of Their Properties

Crystallography Reports - Sm1&nbsp;–&nbsp;ySryF3&nbsp;–&nbsp;y (0 &lt; y ≤ 0.31) crystals have been grown from melt by directional solidification in a...     

Corrosion behavior of Fe-based ferromagnetic (Fe,Ni)–B–Si–Nb bulk glassy alloys in aqueous electrolytes

Fe-based ferromagnetic [(Fe_1?xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ (x = 0, 0.2 and 0.4) bulk glassy alloys (BGAs) with a diameter of 2 mm were prepared by copper mold casting. The corrosion behavior of glassy alloy rods obtained was investigated in 0.5 M NaCl, 0.5 M NaOH and 0.5 M H₂SO₄ aqueous electrolytes, respectively, using weight loss and electrochemical polarization measurements. It was found that the corrosion rates significantly decrease with an increase in Ni content in all examined solutions. The Ni-containing BGAs are spontaneously passivated with wide passive regions and low passive current densities in NaCl and NaOH solutions, but exhibit the active–passive–transpassive behavior in H₂SO₄ solution. The partial substitution of Ni for Fe results in a considerable improvement on the corrosion resistance of [(Fe_1?xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ BGAs, because of the structural and chemical homogeneousness of the amorphous phase and the effect of Ni on promoting the formation of a passive film. Besides their high glass-forming ability (GFA), excellent soft-magnetic properties and good mechanical performance, which have been reported before, these FeNi-based BGAs also feature rather high corrosion resistance.     

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.     

Correlation between bulk and surface properties in Cd–X (X = Hg,Mg) liquid alloys

A theoretical investigation of the energetics and its effect on the alloying behaviour of Cd–Hg and Cd–Mg liquid alloys have been carried out with the aim of correlating their bulk and surface phenomena. Using the Quasi-chemical approximation for regular solution model, our results indicate that Cd–Hg and Cd–Mg are weakly heterocoordinated both in the bulk and on the surface. We observed that the degree of chemical order in Cd–Mg liquid alloy is more than that of Cd–Hg liquid alloy.     

Effect of germanium on the microstructure and the magnetic properties of Fe–B–Si amorphous alloys

In this work, we present a systematic study on the crystallization kinetics and the magnetic properties of melt-spun Fe₈₀B₁₀Si_10 ? xGe_x (x = 0.0 ? 10.0) amorphous alloys. The activation energy for crystallization, determined by differential scanning calorimetry, displayed a strong dependence on the Ge content, reflecting a deleterious effect on the alloys' thermal stability and their glass forming ability with increasing Ge concentration. On the other hand, the alloys exhibited excellent soft magnetic properties, i.e., high saturation magnetization values (around 1.60 T), alongside Curie temperatures of up to 600 K. Complementary, for increasing Ge substitution, the ferromagnetic resonance spectra showed a microstructural evolution comprising at least two different magnetic phases corresponding to a majority amorphous matrix and to Fe(Si, Ge) nanocrystallites for x ≥ 7.5.