Crystallization Behavior and Corrosion Resistance of Cu<Subscript>50</Subscript>Zr<Subscript>40</Subscript>Ag<Subscript>10</Subscript> Amorphous Alloy

In this study, Cu₅₀Zr₄₀Ag₁₀ amorphous alloy ribbons were prepared by a single roller melt-spinning method. The crystallization behavior of the Cu₅₀Zr₄₀Ag₁₀ amorphous alloy has been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Moreover, the polarization and passivation behaviors of the as-quenched and as-annealed amorphous alloy have been studied in 1 N H₂SO₄. The surfaces of corroded samples have been examined using scanning electron microscopy (SEM) and the element distribution across the pits has been analyzed using energy dispersive spectrometer (EDS). The results show that the Cu₅₀Zr₄₀Ag₁₀ amorphous alloy has a large supercooled region up to 36 K. The ω-(ZrCu), ZrO₂ and Cu₁₀Zr₇ phases can firstly precipitate from the amorphous matrix below glass transition temperature during annealing for 30 min. Moreover, the corrosion resistance of the as-quenched amorphous alloy is better than that of partial and full crystallization products. In addition, Zr plays a crucial role in enriching the passive film and enhancing corrosion resistance.     

Crystallization Behavior and Mechanical Properties of Mg86.33Ni12.67Y1 Amorphous Alloy

Mg_86.33Ni_12.67Y₁ amorphous alloy was obtained by a single-roller melt-spinning technique and some samples were isothermally annealed at different temperatures. The glass-forming ability (GFA), crystallization behavior and the effect of annealing treatment on the mechanical properties of the alloy were studied. The results show that for Mg_86.33Ni_12.67Y₁ amorphous alloy, the reduced glass transformation value T_rg (T_rg = T_g/T_l) is 0.5089 and the width of super-cooled liquid region (ΔT_x) is 40.08 K. When the samples were annealed at 413 K, the degree of short-range order of the amorphous atoms as well as the micro-hardness, increased due to structural relaxation, with increasing time, completing at 10 min. Significant crystallization of the Mg_86.33Ni_12.67Y₁ alloy occurred after annealing above 443 K, and two crystalline phases, Mg₆Ni and Ni₇Y₂ were precipitated into the amorphous matrix. With increasing annealing temperature (range: 573–653 K), Mg₆Ni crystals were gradually transformed into Mg₂Ni and α-Mg. The micro-hardness decreased significantly with temperatures above 413 K. This was accompanied by a decrease in free volume of the matrix during the crystallization of the two phases.     

Non‐isothermal crystallization kinetics of Al2O3‐YAG amorphous ceramic coating deposited via plasma spraying

Crystallization kinetics of the newly developed Al₂O₃‐Y₃Al₅O₁₂ (YAG) amorphous ceramic coating fabricated by atmospheric plasma spraying (APS) were investigated via differential scanning calorimetry (DSC) under non‐isothermal conditions. The phase compositions and microstructure of the as‐sprayed coating were characterized by X‐ray diffraction (XRD) and Scanning electron microscopy (SEM). The glass transition temperature T_g, the onset temperature of crystallization T_c and the peak temperature of crystallization T_p presented heating rate dependence. The related kinetic parameters of activation energies (E_g, E_c, E_p) and Avrami exponents (n) were quantified using various methods including Kissinger, Augis–Bennett, Ozawa and Matusita–Sakka, etc., to understand the phase transition mechanism and crystallization process in depth. A series of parameters including devitrification interval ΔT, thermal stability (T_c, E_c), nucleation resistance E_c/RT_g and fragility index F were quantified in order to evaluate the nucleation mechanism, crystallization behavior and thermal stability of Al₂O₃‐YAG amorphous ceramic coating. Excellent thermal stability was witnessed in the studied coating. Furthermore, the YAG crystalline phases can be reasonably controlled and independently precipitated from the amorphous matrix via proper annealing.     

Investigation into the phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> system

Nanopowders of solid solutions with different compositions are prepared in the zirconia-enriched region of the ZrO₂-CeO₂ system. The crystallization of these powders and the formation of the monoclinic, cubic, and tetragonal solid solutions of the composition (Zr_{1 – x} Ce_x)O₂ are investigated. It is found that the unit cell parameters of the solid solutions increase as the cerium content increases. This confirms the fact that cerium ions [r(Ce⁴⁺) = 1.11 ] substitute for zirconium ions [r(Zr⁴⁺) = 0.98 ] in these solid solutions. The average size of crystallites of the solid solutions under investigation increases from 5 to 60 nm in the temperature range 500–1200°C.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Panova, Glushkova, Nefedova.     

Structure and properties of solid solutions of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BaCuFeO<Subscript>5 + δ</Subscript>

The effect of replacing lanthanum with praseodymium on the crystal chemistry parameters of solid solutions of La_{1 − x} Pr _x BaCuFeO_{5 + δ} has been investigated using X-ray powder diffraction analysis and IR spectroscopy. The thermal expansion, electroconductivity, and thermopower of these phases have been studied in air in the temperature range 300–1100 K. The values of linear thermal expansion coefficients (LTEC) of ceramics in different temperature ranges have been determined, and the values of electric transfer parameters in the above oxides have been calculated. It has been established that replacing lanthanum with praseodymium resulted in the compression of the elementary oxide unit La_{1 − x} Pr _x BaCuFeO_{5 + δ}, decrease in the content of labile oxygen in them (δ), decrease in nonmonotonic electroconductivity, increase in thermopower, decrease in LTEC, and difficulties in charge transfer in these phases.     

Analysis of the atomic structure of metallic glass of composition Al<Subscript>87</Subscript>Ni<Subscript>10</Subscript>Nd<Subscript>3</Subscript> with the use of a fragmentary model

Use of a fragmentary model in the analysis of the atomic structure of an Al₈₇Ni₁₀Nd₃ amorphous metal alloy made it possible to determine that it has fragments of the structures of three phases, namely, Al, Al₃Ni, and Al₃Nd. After crystallization of the alloy under the action of pulse photon irradiation, polycrystals of pure aluminum and two Al₃Ni and Al₄Nd intermetallides were found in it. Because fragments of structure Al₄Nd were not observed in the amorphous state, it follows that atoms which form fragments structure Al₃Nd rearrange to structure Al₄Nd upon crystallization.     

Photoluminescence characteristics of Cd<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te single crystals grown by the vertical Bridgman method

In this paper, we report a systematic investigation of band-edge photoluminescence for Cd_1-x Mn _x Te crystals grown by the vertical Bridgman method. The near-band-edge emissions of neutral acceptor-bound excitons (labeled as L1) were systematically investigated as a function of temperature and of alloy composition. The parameters that describe the temperature variation of the energy were evaluated by the semiempirical Varshni relation. From the temperature dependence of the full width at half maximum of the L1 emission line, the broadening factors Γ(T) were determined from the fit to the data. The activation energies of thermal quenching were obtained for the L1 peak from the temperature dependence of the bound exciton peaks and were found to decrease with increasing Mn concentration.     

Structure characterization of amorphous Al83Ni10Ce5Si2 under the relaxed annealing

In order to trace the structure evolution of amorphous Al₈₃Ni₁₀Ce₅Si₂ before crystallization, the alloy viscosity (η) was measured by methods after annealing treatment at various temperatures. It is found that the alloy viscosity decreases initially and then increases with the annealing temperature. The X-ray diffraction (XRD) patterns show that the variation of the height of the main peak with annealing temperature (H _max − T) is similar to that of the viscosity versus anncaling temperature (η − T), implying that the short-range order (SRO) in the amorphous alloy has changed. Additionally, the locations of the main peak and prepeak in the XRD curves move toward the high angle, implying that the characteristic spacing in the amorphous alloy decreases and that its volume decreases with the increase of the annealing temperature. The volume decrease is also confirmed by the development of the grooves on the free surface of the amorphous ribbon. The text was submitted by the authors in English.     

Combustion and structure formation in the Ti-Ta-C-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> system

Biocompatible composites (Ti, Ta)C _x + Ca₃(PO₄)₂ for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca₃(PO₄)₂ mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have little or no influence on the burning velocity U and combustion temperature T _c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.      

Poole-Frenkel photoconductivity in amorphous Se<Subscript>75</Subscript>Te<Subscript>20</Subscript>Sb<Subscript>5</Subscript> thin films

In many amorphous and liquid semiconductors and many other class of materials, pre-exponential factor of electrical conductivity σ₀ is found to increase exponentially with activation energy ΔE according to Meyer-Neldel rule. This rule is generally verified by selecting different compositions of different ΔE in a given class of materials. In the present paper, we report the investigation of Meyer-Neldel rule (MN rule) for the pre-exponential factor (σ _ph )₀ and activation energy of (ΔE _ph ) photoconductivity in amorphous thin films of Se₇₅Te₂₀Sb₅ for high field conduction. The photoconduction was found to be ohmic at low fields and of Poole-Frenkel type at high fields. In the present work we have changed ΔE _ph by applying high electric fields.     

Design of Efficient Ce<Subscript>x</Subscript>M<Subscript>1−x</Subscript>O<Subscript>2−δ</Subscript> (M = Zr,Hf, Tb and Pr) Nanosized Model Solid Solutions for CO Oxidation

Abstract  

Nanosized Ce_xM_1−xO_2−δ (M = Zr, Hf, Tb and Pr) solid solutions were prepared by a modified coprecipitation method and thermally treated at different temperatures from 773 to 1073 K in order to ascertain the thermal behavior. The structural and textural properties of the synthesized samples were investigated by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), BET surface area, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) techniques. The catalytic efficiency has been performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. The characterization results indicated that the obtained solid solutions exhibit defective cubic fluorite structure. The solid solutions of ceria–hafnia, ceria–terbia and ceria–praseodymium exhibited good thermal stability up to 1073 K. A new Ce_0.6Zr_0.4O₂ phase along with Ce_0.75Zr_0.25O₂ was observed in the case of ceria–zirconia solid solution due to more Zr⁴⁺ incorporation in the ceria lattice at higher calcination temperatures. The reducibility of ceria has been increased upon doping with Zr⁴⁺, Hf⁴⁺, Tb^3+/4+ and Pr^3+/4+ cations. This enhancement is more in case of Hf⁴⁺ doped ceria. Among various solid solutions investigated, the ceria–hafnia combination exhibited better OSC and CO oxidation activity. The high efficiency of Ce–Hf solid solution was correlated with its superior bulk oxygen mobility and other physicochemical characteristics.     

Structural Relaxation Phenomenon in Amorphous Al85Ni10Ce5 Alloy during Natural Aging

The structural relaxation phenomenon in amorphous Al₈₅Ni₁₀Ce₅ alloy during natural aging has been investigated. It has been found that the crystallization temperature (T _p) increases with increasing relaxation time () during the natural structural relaxation, indicative of a higher thermal stability of the alloy. After the structural relaxation, the crystallization temperature and thermal stability become invariable with increasing aging time. Based on X-ray diffraction measurements, it has been assumed that this effect is attributed to the structural unit corresponding to the prepeak, transforming from defective icosahedra to normal icosahedra composed of 13 atoms with Ni as the central atom. With the structural relaxation complete, the double icosahedra or the atomic clusters of icosahedra are formed, which leads to a higher short-range order.     

Investigation of a new lead-free Bi<Subscript>0.5</Subscript>(Na<Subscript>0.40</Subscript>K<Subscript>0.10</Subscript>)TiO<Subscript>3</Subscript>-(Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>)TiO<Subscript>3</Subscript> piezoelectric ceramic

Lead-free piezoelectric compositions of the (1-x)Bi_0.5(Na_0.40K_0.10)TiO₃-x(Ba_0.7Sr_0.3)TiO₃ system (when x = 0, 0.05, 0.10, 0.15, and 0.20) were fabricated using a solid-state mixed oxide method and sintered between 1,050°C and 1,175°C for 2 h. The effect of (Ba_0.7Sr_0.3)TiO₃ [BST] content on phase, microstructure, and electrical properties was investigated. The optimum sintering temperature was 1,125°C at which all compositions had densities of at least 98% of their theoretical values. X-ray diffraction patterns that showed tetragonality were increased with the increasing BST. Scanning electron micrographs showed a slight reduction of grain size when BST was added. The addition of BST was also found to improve the dielectric and piezoelectric properties of the BNKT ceramic. A large room-temperature dielectric constant, ε _r (1,609), and piezoelectric coefficient, d ₃₃ (214 pC/N), were obtained at an optimal composition of x = 0.10.     

Effect of annealing treatments on photoluminescence and charge storage mechanism in silicon-rich SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H films

In this study, a wide range of a-SiN _x :H films with an excess of silicon (20 to 50%) were prepared with an electron-cyclotron resonance plasma-enhanced chemical vapor deposition system under the flows of NH₃ and SiH₄. The silicon-rich a-SiN _x :H films (SRSN) were sandwiched between a bottom thermal SiO₂ and a top Si₃N₄ layer, and subsequently annealed within the temperature range of 500-1100°C in N₂ to study the effect of annealing temperature on light-emitting and charge storage properties. A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C. The possible origins of the PL are briefly discussed. The authors have succeeded in the formation of amorphous Si quantum dots with an average size of about 3 to 3.6 nm by varying excess amount of Si and annealing temperature. Electrical properties have been investigated on Al/Si₃N₄/SRSN/SiO₂/Si structures by capacitance-voltage and conductance-voltage analysis techniques. A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices.     

Direct Synthesis of Dimethyl Carbonate from Methanol and Carbon Dioxide over Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>/Ce<Subscript>0.6</Subscript>Zr<Subscript>0.4</Subscript>O<Subscript>2</Subscript> Catalysts: Effect of Acidity and Basicity of the Catalysts

Abstract  

Ce _X Zr_1−X O₂ catalysts with different cerium content (X) (X = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0) were prepared by a sol–gel method for use in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Among these catalysts, Ce_0.6Zr_0.4O₂ was found to show the best catalytic performance. In order to enhance the acidity and basicity of Ce_0.6Zr_0.4O₂ catalyst, Ga₂O₃ was supported on Ce_0.6Zr_0.4O₂ (XGa₂O₃/Ce_0.6Zr_0.4O₂ (X = 1, 5, 10, and 15)) by an incipient wetness impregnation method with a variation of Ga₂O₃ content (X, wt%). Effect of acidity and basicity of Ga₂O₃/Ce_0.6Zr_0.4O₂ on the catalytic performance in the direct synthesis of dimethyl carbonate was investigated using NH₃-TPD and CO₂-TPD experiments. Experimental results revealed that both acidity and basicity of the catalysts played a key role in determining the catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. Large acidity and basicity of the catalyst facilitated the formation of dimethyl carbonate. The amount of dimethyl carbonate produced over XGa₂O₃/Ce_0.6Zr_0.4O₂ catalysts increased with increasing both acidity and basicity of the catalysts. Among the catalysts tested, 5Ga₂O₃/Ce_0.6Zr_0.4O₂, which retained the largest acidity and basicity, showed the best catalytic performance in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide.     

Improved electrochemical properties of Li(Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript>)O<Subscript>2</Subscript> cathode for lithium ion batteries with controlled sintering conditions

Improved electrochemical properties of Li(Ni_0.7Co_0.3)O₂ cathode material are reported. Samples were synthesized by the co-precipitation method with various sintering conditions, namely temperature, time and atmosphere. Li(Ni_0.7Co_0.3)O₂ sintered at 850 °C for 14 h in air exhibited the lowest unit cell volume accompanied with relatively higher values of c/a and I ₁₀₃/I ₁₀₄ reflection peaks ratios. This also exhibited superior electrochemical properties, such as high charge–discharge capacity, high Coulombic efficiency, and low irreversible capacity loss. This can be attributed to improved hexagonal ordering, crystallinity and morphology. The electrochemical cell parameters were better than the reported ones, probably due to controlled sintering conditions.     

SHS of Y<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>-based mineral-like ceramics: Influence of green density

Explored was the influence of compacting pressure (P) and green density (ρ) on the properties of Zr-doped mineral-like pyrochlore ceramics Y₂(Ti_{1 – x} Zr _x )₂O₇ (x ≤ 0.3) prepared by SHS method. The optimal ρ values that provide minimal porosity and maximal mechanical strength of synthesized ceramics were found. An increase in ρ was found to decrease combustion temperature and increase pyrochlore lattice parameter a. Green density was also found to affect phase composition of the SHS-produced ceramics under study.     

Fabrication and Magnetic Properties of Fe<Subscript>65</Subscript>Co<Subscript>35</Subscript>–ZnO Nano-Granular Films

A series of nano-granular films composed of magnetic metal (Fe₆₅Co₃₅) granules with a few nanometers in size and semiconductor oxide (ZnO) have been fabricated by a magnetron sputtering method, and excellent soft magnetic properties have been achieved in a wide metal volume fraction (x) range for as-deposited samples due to the exchange coupling between FeCo granules (a ferromagnetic interaction in nano-scale). In a wide range (0.53 < x < 0.71), the films exhibit coercivity H _C not exceeding 15 Oe, along with high resistivity. Especially for the sample with x = 0.67, coercivities in hard and easy axes are 1.43 and 7.08 Oe, respectively, 4πM _S  = 9.85 kg, and ρ reaches 2.06 × 10³ μΩ cm. The dependence of complex permeability μ = μ′ − jμ″ on frequency shows that the real part μ′ is more than 100 below 1.83 GHz and that the ferromagnetic resonance frequency reaches 2.31 GHz, implying the promising for high frequency application. The measured negative temperature coefficient of resistivity reveals that may be the weak localized electrons existing in samples mediate the exchange coupling.     

Viscoelastic,thermal, and morphological analysis of HDPE/EVA/CaCO<Subscript>3</Subscript> ternary blends

High density polyethylene (HDPE), calcium carbonate (CaCO₃), and ethylene vinyl acetate (EVA) ternary reinforced blends were prepared by melt blend technique using a twin screw extruder. The thermal properties of these prepared ternary blends were investigated by differential scanning calorimetry. The effect of EVA loading on the melting temperature (T _m) and the crystallization temperature (T _C) was evaluated. It was found that the expected heterogeneous nucleating effect of CaCO₃ was hindered due to the presence of EVA. The melt viscosities of the ternary reinforced blends were affected by the % loading of CaCO₃, EVA, and vinyl acetate content. Viscoelastic analysis showed that there is a reduction of the storage modulus (G′) with increasing of EVA loading as compared to neat HDPE resin or to HDPE/CACO₃ blends only. The morphology of the composites was characterized by scanning electron microscopy (SEM). The dispersion and interfacial interaction between CaCO₃ with EVA and HDPE matrix were also investigated by SEM. We observed two main types of phase structures; encapsulation of the CaCO₃ by EVA and separate dispersion of the phases. Other properties of ternary HDPE/CaCO₃/EVA reinforced blends were investigated as well using thermal, rheological, and viscoelastic techniques.     

Thermoelectric Properties of <Emphasis Type="Italic">x</Emphasis>PbTe/Yb<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Hot-Pressed Samples

The xPbTe/Yb_0.2Co₄Sb₁₂ compounds were prepared by the ball-milling and hot-pressed process. Electrical conductivity of the composite samples are reduced with a increase in PbTe content; and, their temperature dependence coefficients show the positive values. The maximum electrical conductivity of composite materials is ~80000 Sm⁻¹ at 800 K. The Seebeck coefficient (absolute value) of the composite material is obviously improved with an increase in the dispersed phase (PbTe) content; the Seebeck coefficient (absolute value) of the 10PbTe sample is ~260 μVK⁻¹ at 700 K, which increases by 13.6% relative to that of the Yb_0.2Co₄Sb₁₂ sample. The thermal conductivity of the composite samples is improved due to introduction of PbTe, and the thermal conductivity of the 10PbTe sample is ~3 Wm⁻¹ K⁻¹ at 550 K. The maximum value of ZT is 0.78 at 700 K for the 2.5PbTe sample.