Investigation of primary Al3(Sc,Zr) particles in Al–Sc–Zr alloys

Abstract

This paper studied the primary Al₃(Sc,Zr) particles formed during solidification in three Al–Sc–Zr alloys with various Zr contents. It has been shown that the primary Al₃(Sc,Zr) particles formed during solidification since the Sc and Zr concentrations are above the solid solubility limit in Al matrix. Scanning electron microscopy line scanning results indicated that the distributions of Sc, Zr and Al atoms in the primary Al₃(Sc,Zr) particles differ a lot from those in the secondary Al₃(Sc,Zr) particles formed during annealing. In the primary Al₃(Sc,Zr) particles, both Sc and Zr contents are found from rim to the centre of the particles, with an increasing trend from the rim to the centre, while the Al content drops sharply on the rim of the particle and slightly from the rim to the centre.     

Preparation of xTiO2·(1 − x)Al2O3 catalytic supports by the sol-gel method: physical and structural characterisation

A series of xTiO₂·(1 – x)Al₂O₃ mixed oxides has been prepared by the sol-gel method with variable amounts of TiO₂, from pure alumina to pure titania. Textural, bulk and surface characterisation of the samples has been carried out by nitrogen physisorption (S _BET, porosity), thermal analysis (TGA, DTA), X-ray diffraction (XRD), zero point charge (ZPC) and surface acidity. The textural results show that at low titania contents, higher surface areas than those of pure alumina are obtained, and in the titania-rich samples, higher surface areas than for pure titania are stabilised. The titanium content also affects the crystallization process. Furthermore, the strength and distribution of the acid sites may be varied by changing the composition of the mixed oxide.     

Synthesis and properties of dielectric (HfO2)1 − x (Sc2O3) x films

(HfO₂)_{1 ? x} (Sc₂O₃) _x films have been grown by chemical vapor deposition (CVD) using the volatile complexes hafnium 2,2,6,6-tetramethyl-3,5-heptanedionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptanedionate (Sc(thd)₃) as precursors. The composition and crystal structure of the films containing 1 to 36 at % Sc have been determined. The results demonstrate that, in the composition range 9 to 14 at % scandium, the films are nanocrystalline and consist of an orthorhombic three-component phase, which has not been reported previously. Using Al/(HfO₂)_{1 ? x} (Sc₂O₃) _x /Si test structures, we have determined the dielectric permittivity of the films and the leakage current through the insulator as functions of scandium concentration. The permittivity of the films with the orthorhombic structure reaches k = 42–44, with a leakage current density no higher than ～10^?8 A/cm².     

Powders of Pb(ZrxTi1−x)O3 by sol-gel coating of PbO

Powders of lead zirconate titanate (PZT) are prepared by coating a PbO powder with very fine particles containing titanium and zirconium derived from an alkoxide sol. The size of the particles in the coating increases from 10 nm to 100 nm with the increase in the pH during preparation from 3 to 10.5. The powders calcine at low temperature ( 600 °C) to single-phase PZT without the formation of any intermediate phase. The tetragonal and rhombohedral phases are found to coexist betweenx = 0.535 and 0.545. Careful calcination of the powders is needed to ensure removal of residual organics; otherwise the residual carbon reduces PbO to metallic lead leading to high currents during poling. Loss of lead on sintering is significantly lower (1.4 wt%) as compared to samples from conventional powders (6.4 wt%). Successful poling of the sintered samples is achieved when the powders are prepared without using sol stabilizers and are calcined without pelletizing. Washing of the powders is not helpful, perhaps because it leads to change in stoichiometry due to loss of material. A dielectric constant of 950 andd ₃₃ > 190 pCN^–1 are easily achieved.     

The investigation of structural and magnetic properties of Er2−xCoxO3 nano-oxides

Journal of Materials Science: Materials in Electronics - The sol–gel technique was used to synthesize Er2?xCoxO3 (0.0?≤?x?≤?0.30) mixed oxides to...     

Effect of calcium on the structural properties of Ba(1−x)Ca x TiO3 particles synthesized by complex polymerization method

Ferroelectric materials, such as barium titanate (BaTiO₃), have been extensively studied for application in electronic and optical devices. The substitution of Ba by Ca is an effective method to improve the piezoelectricity temperature stability, as it can greatly lower the tetragonal–orthorhombic phase transition temperature, whereas the change of the Curie point is negligible. Ba_(1?x)Ca _x TiO₃ (x = 0, 0.05, 0.10, 0.15, and 0.20) powders were prepared by complex polymerization method. The effect of calcium on the tetragonality of the BaTiO₃ system was monitored using basic characterization techniques: X-ray diffraction, differential scanning calorimetry, and Raman spectroscopy. The results indicate that increased calcium contents raise the Curie temperature (T _c) and that the addition of calcium in the BT matrix reduces tetragonality.     

Preparation,structural and spectroscopic studies of (YxLu1−x)2O3:Eu3+ nanopowders

Lutetium and yttrium oxides are promising scintillating materials suitable for use in medical planar X-ray imaging and mammography. In this paper the procedure for preparation of europium doped mixed lutetium–yttrium oxide nanopowders using polymer complex solution synthesis method is presented. Detailed information on nanopowder phase, morphology and crystallinity are obtained using X-ray powder diffraction, SEM and TEM while optical properties are investigated by photoluminescence and radioluminescence measurements. Constituting nanoparticles are 20–40 nm in size, and have excellent structural ordering in cubic bixbyite-type. Unit cell parameter, ionic coordinates, crystal coherence size and microstrain are determined from Rietveld analysis. All powders show strong Eu³⁺-characteristic red emission, with an average ⁵D₀ emission lifetime of 1.5 ms. Radioluminescence efficiency is about 15% of the commercial micron-sized Gd₂O₂S:Eu³⁺ powder while negligible level of afterglow is found.     

Effect of Al content on the performance of Cu(In1−x Al x )S2 synthesized by hydrothermal solution processing

Al doped CuInS₂ (CIS) material was prepared by a low cost and non vacuum wet chemical process. The effect of aluminum concentrations on the crystal structure, morphology, percentage composition, and band gap of Cu(In_{1? x} Al _x )S₂ were investigated. The X-ray diffraction (XRD) shows that the size of crystal grains decreased with the increase of Al concentrations. Scanning electron microscope presents the size of particles is gradually become smaller with Al concentrations increase. The reason for these phenomenons is Al concentrations cause the solution to a colloidal state. Binding between ions and grains growing together gradually become harder in a colloidal solution. In situ XRD tests show that CIS perform exceptional thermal stability below 798 K but decomposed to Cu₂S and In₂S₃ at the temperature higher than 798 K. Results of energy dispersive X-ray analysis (EDAX) show the nearly stoichiometry composition of Cu(In_{1? x} Al _x )S₂ which matched well with the ratio of the precursor solution. The transmission spectra show that spectral transmittance decrease with decreasing contents of Al. The band gap of Cu(In_{1? x} Al _x )S₂ is continuously tuned in a range of 1.56–1.92 eV as Al/(Al + In) content ratio varied from 0 to 0.3. Finally, the mechanism of Al concentration on the properties of Cu(In_{1? x} Al _x )S₂ was discussed briefly.     

The evolution of structure and properties in GdMn(1−x)TixO3 ceramics

In this work, the effects of Ti doping on the microstructure, dielectric, and magnetic properties of GdMn_(1?x)Ti_xO₃ (x?=?0.00–0.15) ceramic samples synthesized using a solid-state reaction were investigated. All the experimental samples formed a single-phase structure, and no structural transformation occurred within the experimental doping range; however, Ti doping caused lattice shrinkage. Ti doping reduced the grain size, and the microstructure of the synthesized samples appeared more compact in scanning electron microscopy images. The lattice distortion of GdMn_(1?x)Ti_xO₃ caused by Ti substitution at the Mn sites resulted in changes in the Raman vibration modes. X-ray photoelectron spectroscopy results showed that the valence state transition of the Ti and Mn ions occurred and the concentration of Ti⁴⁺, Mn³⁺ ions and oxygen vacancies changed due to the charge compensation induced by Ti doping. Ti doping had a significant influence on the size and concentration of cation vacancies in the GdMn_(1?x)Ti_xO₃ samples. Appropriate Ti doping was shown to reduce the dielectric loss, improve the frequency stability of the dielectric constant, and significantly affect the long-range ordering of Gd³⁺ magnetic moments and clearly reduce magnetization.

     

Atomic and electronic structure of the Si(111)-√3x√3-Ag surface reexamined using first-principles calculations

We have reexamined the atomic and electronic structures of the Si(111)-√3x√3-Ag surface using first-principles calculations within the local density functional approach. First, we found that a discrepancy among previous first-principles studies concerning the honeycombchained- triangle (HCT) model, which was believed to describe the structure of the surface, can be attributed to the difference in the structural parameters adopted in the calculations. Second,we have confirmed that the recently proposed inequivalent triangle (IET) model, where the positions of the Ag atoms are distorted a little from those in the HCT, is energetically more stable than the HCT one. We have also examined several othermodels that have distortions similar to the IET one. The results suggest that at room temperature the surface does not stay in the HCT configuration, but fluctuates between various configurations.     

Sol–gel synthesis and properties of YBa2(Cu1−xMx)4Oy (M=Co,Ni) and effects of additional replacement of yttrium by calcium

In this work the influence of replacing Cu by Ni or Co on the structural and superconducting properties of YBa₂Cu₄O₈ is studied by means of XRD, TGA, SEM, EDX and resistivity measurements. The samples are prepared by the acetate–tartrate sol–gel method, which has proved to be very appropriate for the synthesis of Y-124 at 1 atm with even very small amounts of dopants. It is demonstrated that the transition temperature drastically decreases upon Co or Ni substitution, and that superconductivity is lost at 3% Ni and 6% Co doping. XRD measurements show that Ni and Co produce different structural effects to the orthorhombic YBa₂Cu₄O₈ phase, possibly because they are introduced in different copper positions. Interesting results are obtained by additional substitution of Y by Ca in the Co- and Ni-doped samples: It is shown that the superconducting properties are enhanced in the samples with less than 3% Ni or 6% Co, and that superconductivity is even recovered in samples with more than 3% Ni or 6% Co.     

Growth,structural and optical characterizations of LiLa(1−x)Eux(WO4)2 single-crystalline fibers by the micro-pulling-down method

Transparent and uniform LiLa_(1?x)Eu_x(WO₄)₂ single-crystalline fibers where x = 0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25 and 1.0, with an average of 20–40 mm length were obtained by the micro-pulling-down method aiming structural and optical characterization. The optimum pulling rate was found to depend on the difference between alkali and rare earth ionic radii. Rietveld analysis from X-ray diffraction data and excitation spectroscopy at room temperature were applied to investigate the lattice changes due to the Eu³⁺ incorporation in the host. LiLa_(1?x)Eu_x(WO₄)₂ crystal fibers present red emission due to the electric dipole ⁵D₀ → ⁷F₂ transition under 395 nm excitation showing a concentration quenching around 20 mol% of doping. The excitation spectra of the ⁷F₀ → ⁵D₀ transition show small changes in the Eu³⁺ surroundings as function of dopant concentration.     

Theoretical prediction of structural parameters, band-gap energies, and mixing enthalpies of Sc1−x In x As alloys

Structural parameters, band-gap energies, and mixing enthalpies of Sc_1?x In _x As alloys were calculated using the full-potential linearized–augmented plane wave method. These calculations are based on density functional theory, within local density approximation, and generalized gradient approximation for the exchange and correlation potential. Given that the binary precursor compounds ScAs and InAs crystallize in rock-salt and zinc-blende, respectively, we made calculations for the ternary alloys in these two phases. The effect of composition x on structural parameters, band-gap energies, and mixing enthalpies was analyzed for x = 0, 0.25, 0.5, 0.75, 1. The effect of atomic composition on lattice constant, bulk modulus, and band-gap energy shows nonlinear dependence on concentration x. Deviations of the lattice constant from Vegard’s law and deviations of the bulk modulus and gap-energy from linear concentration dependence were found. We have found a metallic character for rock-salt Sc_1?x In _x As alloys, while the zinc-blende Sc_1?x In _x As alloys are semiconductors. Our results show that the band-gap undergoes a direct ( $X \rightarrow X$ )-to-direct ( $\Upgamma\rightarrow \Upgamma$ ) transition at a given indium composition. The physical origin of the band-gap bowing in zinc-blende Sc_1?x In _x As alloys was investigated. To study the thermodynamic stability of Sc_1?x In _x As alloys, a regular-solution model was used. This resulted in lower mixing enthalpies for zinc-blende Sc_1?x In _x As alloys.     

Synthesis and characterisation of nanostructured Al–Al3V and Al–(Al3V–Al2O3) composites by powder metallurgy

In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al₃V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al₃V–Al₂O₃ reinforcement was synthesised by mechanochemical reduction during milling of V₂O₅ and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al₃V and Al-10?wt-% (Al₃V–Al₂O₃) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C.     

Synthesis of compositionally homogeneous Pb(ZrxTi1−x)1−y(Mg1/3Ta2/3)yO3 by wet–dry combination method and its dielectric properties

Ternary perovskite-type solid solutions of Pb(Zr_xTi_1−x)_1−y(Mg_1/3Ta_2/3)_yO₃ (PZTMT) were synthesized by a wet–dry combination method in which a coprecipitation process was applied to B-site cations (Zr⁴⁺, Ti⁴⁺, Mg²⁺ and Ta⁵⁺). The compositional homogeneity in calcined powders and dielectric properties of sintered ceramics were investigated. The powder X-ray diffraction analysis revealed that PZTMT powders prepared by the wet–dry combination method had no compositional fluctuation unlike that prepared by a conventional dry method. The sintered PZTMT prepared by the wet–dry combination method exhibited much higher dielectric constant than that prepared by the conventional dry method. The improvement of the compositional homogeneity and the density led to the improvement of the dielectric properties.     

The HREM study of precipitates in an Al−Zn−Mg alloy

A study of precipitate phases in an Al–Zn–Mg alloy in the T74 condition has been conducted by means of high resolution electron microscopy. It has been observed that G.P. zones, and phases exist simultaneously in the matrix. The G.P. zones are plate-like forming on (111) matrix plane. The phase has a hexagonal structure witha=0.496 nm,c=1.403 nm and the orientation relationship with the matrix is . A new orientation relationship between the phase and the matrix is found to be .     

Electrical properties of nanostructures (CoFeZr)x + (Al2O3)1−x with use of alternating current

CoFeZr–Al₂O₃ nanocomposite films of 3–5 μm thickness, containing metallic alloy nanoparticles embedded into the dielectric alumina matrix, have been deposited on a glass ceramic substrate using magnetron sputtering of composite target in Ar gas ambient. Measurements of AC conductance and lagging have been performed within the frequency range of 50 Hz–1 MHz at the temperatures from 79 K to 373 K in the initial (as-deposited) samples as well as directly after their isochronous (15 min) annealings within the temperature range from 398 K to 648 K with 25 K step.The observed variations of real part AC electrical conductivity with temperature and frequency σ_real(T, f) in the as-deposited films display transition from dielectric to metallic behaviour when crossing the percolation threshold x_C in the studied nanocomposites. After annealing of the samples below the x_C the σ_real(T, f) progress follows the hopping law of electron conductivity with sigmoidal frequency dependence. The samples being far beyond the percolation threshold revealed transition from metallic to activational σ_real(T) law after high-temperature annealing attributed to the internal oxidation of metallic nanoparticle by excess of oxygen presented in the as-deposited samples.     

Superstructures exhibited by oxides of the aurivillius family, (Bi2O2)2+ (An−1BnO3n+1)2−

Bi₅Ti₃FeO₁₅ and Bi₇Ti₃Fe₃O₂₁ which are n=4 and n=6 members of the family of oxides of the general formula (Bi₂O₂)²⁺(A_n−1B_nO_3n+1)²⁻ show unusual superstructures, possibly due to cation ordering.