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.     

Electronic properties calculation of Ge1 − x − ySixSny ternary alloy and nanostructure

The band structure of Ge_{1 ? x ? y}Si_xSn_y ternary alloys, which are easier to grow than binary Ge_1-xSn_x alloys, and clearly offer a wider tunability of their direct band-gap and other properties, was calculated and investigated by using the empirical pseudo-potential plane wave method with modified Falicov pseudo-potential formfunction. The virtual crystal approximation (VCA) and 2 × 2 × 2 super-cell (mixed atoms) method were adopted to model the alloy. In order to calculate all of these properties, the empirical pseudo-potential code was developed. The lattice constant of the alloy varies between 0.543 to 0.649 nm. The regions in the parameter space that corresponds to a direct or indirect band gap semiconductor are identified. The Ge_{1 ? x ? y}Si_xSn_y ternary alloy shows the direct band gap for appropriate composition of Si, Ge and Sn. The direct energy gap is in the range 0–1.4 eV (from the VCA calculation), and 0–0.8 eV (from the super-cell calculation), depending on the alloy composition. Therefore, this alloy is a promising material for optoelectronic applications in both visible and infrared range, such as interband lasers or, solar cells. Furthermore, strain-free heterostructures based on such alloys are designed and, using the effective-mass Hamiltonian model, the electronic structure of GeSiSn quantum wells with arbitrary composition is investigated, in order to understand their properties and the potential of their use in devices.     

Formation and mechanical behavior of (Fe0.5Ni0.5)80−xMoxB20 (x = 0–8) amorphous alloys

Glass forming ability, thermal stability and mechanical behavior of (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ (x = 0, 2, 4, 6, 8) amorphous alloys were studied by XRD, TEM, SEM, DSC, tensile test, microhardness test and tearing test. The effects of Mo addition on glass formation, strength and ductility of (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ amorphous alloys were discussed. The substitution of Mo for Fe and Ni simultaneously causes improvement in glass forming ability and thermal stability, and changes the crystallization process. The tensile fracture strength of amorphous alloy depends on both hardness and ductility; the alloy with high hardness and good ductility simultaneously also has a high tensile fracture strength. The (Fe_0.5Ni_0.5)₇₈Mo₂B₂₀ amorphous alloy exhibits good glass forming ability and the highest tensile fracture strength among (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ alloys. Micro-plastic deformation occurred in ductile and brittle amorphous alloys that both show viscous flow characteristics. The mechanical behavior of (Fe_0.5Ni_0.5)_80?xMo_xB₂₀ amorphous alloys is related to the average outer shell electron concentration of metal atoms.     

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.     

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.     

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.     

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.     

Nano-heterogeneous structure of (1-x)KNbO3–xSiO2 glasses in the low glass-forming oxide content range 0.05 ≤ x ≤ 0.3

Glasses with a high content of niobium oxide are of significant interest for electro-optics and nonlinear optics. In the present paper we report the results of the investigation of the submicroscopic structure and nonlinear optical properties of (1-x)KNbO₃–xSiO₂ (KNS) glasses (x = 0.05–0.30) by XRD, SANS, electron microscopy and second harmonic generation (SHG) technique. Vitreous samples were fabricated by rapid melt cooling, via pressing the melt by steel plates, quenching between rotating metal rolls or splat cooling in air or nitrogen flow. Glasses with x < 0.15 are shown to possess a micro-inhomogeneous structure with regions enriched by SiO₂. On the contrary, as-quenched glasses with x > 0.15 are found by SANS to be homogeneous, but form nanostructures enriched by SiO₂ after heat-treatment. At temperatures below ~(T_g + 50 °C), SiO₂-enriched regions grow slightly, whereas their chemical composition shifts considerably closer to SiO₂. The data on the nano-inhomogeneous structure enables clarifying the complicated T_g(x) dependence of KNS glasses. SHG-active KNbO₃ phase precipitates at later stages of crystallization when the glass starts to lose its transparency, and crystallization of perovskite-like KNbO₃ is accompanied by the enhancement of SHG efficiency by several orders of magnitude.     

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.     

The electrical switching and thermal behavior of bulk Ge15Te85 − xSnx and Ge17Te83 − xSnx glasses

Bulk Ge₁₅Te_85 ? xSn_x and Ge₁₇Te_83 ? xSn_x glasses, are found to exhibit memory type electrical switching. The switching voltages (V_t) and thermal stability of Ge₁₅Te_85 ? xSn_x and Ge₁₇Te_83 ? xSn_x glasses are found to decrease with Sn content. The composition dependence of V_t has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge–Te–Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge₁₅Te_85 ? xSn_x and Ge₁₇Te_83 ? xSn_x glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses.     

Square-wave voltammetry and impedance spectroscopy in tin doped melts with the compositions xNa2O · 15Al2O3 · (85 − x)SiO2 (x = 8.5, 11 and 16)

Glasses with the base compositions xNa₂O · 15Al₂O₃ · (85 ? x)SiO₂ (x = 8.5, 11 and 16) doped with 0.5 mol% SnO₂ were investigated by both square-wave voltammetry and impedance spectroscopy in the temperature range from 1300 to 1600 °C. Each recorded square-wave voltammogram exhibits a well pronounced peak attributed to the Sn²⁺/Sn⁴⁺-redox pair. Impedance spectra were measured in a frequency range from 0.1 to 10⁵ s^?1 as a function of the superimposed dc-potential and were simulated using an equivalent circuit taking into account the resistivity of the melt, the electrochemical double layer, a resistor attributed to a kinetically hindered electron transfer and a Warburg parameter which accounts for the diffusion process of Sn⁴⁺ and Sn²⁺ to and from the electrode. Additionally, two impedance elements, a resistor and a capacitance both attributed to adsorption processes were necessary to fit the impedance spectra.     

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.     

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.     

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.     

Structure and properties of the 70Li2S · (30 − x)P2S5 · xP2O5 oxysulfide glasses and glass–ceramics

The 70Li₂S · (30 ? x)P₂S₅ · xP₂O₅ (mol%) oxysulfide glasses were prepared by the melt quenching method. The glasses were prepared in the composition range 0 ≦ x ≦ 10. The glass–ceramics were prepared by heating the glasses over crystallization temperatures. The PO_nS_3?n (n = 1–3) oxysulfide units were produced in the glasses and glass–ceramics by partial substituting P₂O₅ for P₂S₅. In particular, the P₂OS₆^4? unit would be produced by substituting a small amount of P₂O₅ for P₂S₅. The oxygen atoms were incorporated into the Li₇P₃S₁₁ crystal structure because the diffraction peaks of the oxysulfide glass–ceramic shifted to the higher angle side. The glass–ceramic with 3 mol% of P₂O₅ exhibited the highest conductivity of 3.0 × 10^?3 S cm^?1 and the lowest activation energy for conduction of 16 kJ mol^?1. The P₂OS₆^4? dimer units in the oxygen-incorporated Li₇P₃S₁₁ crystal would improve conductive behavior of the Li₂S–P₂S₅ glass–ceramics.     

Effects of Fe2O3 replacement of ZnO on elastic and structural properties of 80TeO2–(20 − x)ZnO–xFe2O3 tellurite glass system

Ternary tellurite glasses with the chemical formula 80TeO₂–(2 ? x)ZnO–xFe₂O₃ (x = 0–15 mol%) have been prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5 MHz and Fourier transform infrared (FTIR) spectroscopy, respectively. Both longitudinal and shear velocity showed a large increase of 3.40% and 4.68%, respectively, at x = 5 mol% before a smaller increase for x > 5 mol%. Interestingly, longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young's modulus (E) recorded similar trends with increase in Fe₂O₃. The initial large increases in shear and longitudinal velocity and related elastic moduli observed at x = 5 mol% are suggested to be due to structural modification which enhances rigidity of the glass network. FTIR analysis showed increase in bridging oxygen (BO) as indicated by the relative intensity of the TeO₄ assigned peaks and increase in intensity of the FeO₆ assigned peak (~ 451 cm^? 1) which indicates that Fe acts as a modifier in the glass network. The increase in rigidity of the glass system is suggested to be due to the increase of BO together with the formation of strong covalent FeO bond. Quantitative analysis based on the bulk compression and ring deformation models showed that the k_bc/k_exp value decreased gradually from 2.41 (x = 0 mol%) to 2.02 (x = 15 mol%) which infers that the glass system became a relatively more open 3D network as Fe₂O₃ was increased.     

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...     

Mössbauer and Magnetic Study of Lanthanum Manganite La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20): Nonstoichiometric and Stoichiometric Composition

Crystallography Reports - Mössbauer and magnetic study of calcium-doped lanthanum manganites La1&nbsp;–&nbsp;xCaxMn0.98Fe0.02O3&nbsp;+&nbsp;δ (x = 0.05, 0.10, 0.20)...     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.