Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

Superconductors Ba_1−xK_xBiO₃ and body-centered double perovskites Ba_1−xK_xBi_1−yNa_yO₃ have been selectively synthesized by a facile hydrothermal route. The appropriate ratio and adding sequence of initial reagents, alkalinity, reaction temperature and time are the critical factors that influence the crystal growth of the compounds. The purity and homogeneity of the crystals were detected by the ICP, SEM, EDX and TEM studies. Magnetic measurements show that the superconducting transition temperatures T_C of Ba_1−xK_xBiO₃ decrease from 22 K (for x = 0.35) to 8 K (for x = 0.55) with increasing the K doping level.     

Structural, electronic, optical and thermodynamic properties of SrxCa1−xO, BaxSr1−xO and BaxCa1−xO alloys

The structural, electronic, optical and thermodynamic properties of Sr_xCa_1−xO, Ba_xSr_1−xO and Ba_xCa_1−xO ternary alloys in NaCl phase were studied using pseudo-potential plane-wave method within the density functional theory. We modeled the alloys at some selected compositions with ordered structures described in terms of periodically repeated supercells. The dependence of the lattice parameters, band gaps, dielectric constants, refractive indices, Debye temperatures, mixing entropies and heat capacities on the composition x were analyzed for x = 0, 0.25, 0.50, 0.75 and 1. The lattice constant for Sr_xCa_1−xO and Ba_xSr_1−xO exhibits a marginal deviation from the Vegard's law, while the Ba_xCa_1−xO lattice constant exhibits an appreciable upward bowing. A strong deviation of the bulk modulus from linear concentration dependence was observed for the three alloys. The microscopic origins of the gap bowing were detailed and explained. The composition dependence of the dielectric constant and refractive index was studied using different models. The thermodynamic stability of these alloys was investigated by calculating the phase diagram. The thermal effect on some macroscopic properties was investigated using the quasi-harmonic Debye model. There is a good agreement between our results and the available experimental data for the binary compounds which may be a support for the results of the ternary alloys reported here for the first time.     

Martensitic transformation and magnetic properties in high-Mn content Mn50Ni50−xInx ferromagnetic shape memory alloys

A series of Mn₅₀Ni_50−xIn_x (x = 9.75, 10, 10.25, 10.5 10.75, and 11) ferromagnetic shape memory alloys with Mn content as high as 50 at.% were prepared. The martensitic transformation (MT), magnetocaloric effect, and magnetoresistance in Mn₅₀Ni_50−xIn_x alloys were investigated. With x increasing from 9.75 to 11, the MT temperature decreased from 270 to 110 K and the Curie temperature of austenite remains relatively constant. Large positive magnetic entropy change and negative magnetoresistance were observed around MT temperatures in these alloys. Large magnetic entropy change and magnetoresistance would be ascribed to the temperature and magnetic field-induced MT in Mn₅₀Ni_50−xIn_x alloys.     

Interplay of microstructural features in Cr1−xAlxN and Cr1−x−yAlxSiyN nanocomposite coatings deposited by cathodic arc evaporation

The interplay between the deposition geometry, the chemical and phase composition, the crystallite size, the lattice strain and the direction and the degree of the preferred orientation of crystallites was investigated in the Cr_1−xAl_xN and Cr_1−x−yAl_xSi_yN nanocrystalline coatings and nanocomposites, which were deposited in cathodic arc evaporation process at different positions of substrates in the deposition apparatus. The different positions of the substrates affected primarily the distance between the samples and the cathodes and consequently the chemical and phase composition of the coatings, the crystallite size, the lattice strain and the preferred orientation of crystallites. In the Cr_1−xAl_xN coatings, the dominating cubic crystallites were preferentially oriented with their 〈111〉 direction perpendicular to the sample surface; this out-of-plane preferred orientation of crystallites was accompanied by a strong in-plane texture. In the Cr_1−x−yAl_xSi_yN coatings, a strong inclination of the {111} texture from the normal direction and a decay of the in-plane preferred orientation were observed in cubic crystallites with increasing silicon (and aluminium) contents.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Synthesis and thermoelectric properties of the PbSe1−xTex alloys

The PbSe_1−xTe_x alloys with x = 0.2, 0.3, 0.5, 0.85 and 1.0 were prepared by induction melting, ball milling and spark plasma sintering techniques. The thermoelectric properties of the samples were investigated. The XRD analysis indicated that all samples are NaCl-type structure solid solutions Pb(Se,Te) containing nanograins. Increasing Te content resulted in increasing the lattice parameter a. The thermoelectric measurements show that all samples are n-type semiconductors in temperature range from 300 K to 673 K. The electrical resistivity of the doped sample is much smaller than that of pure PbSe, but comparable to that of PbTe. The absolute Seebeck coefficients for the doped sample PbSe_1−xTe_x with x = 0.2, 0.3 and 0.5 range from 150 μV/K at 300 K to 250 μV/K at 673 K, which is much larger than that of pure PbSe (66-138 μV/K), but smaller than that of PbTe (230-310 μV/K) in the same experimental conditions. The thermal conductivity for the doped sample PbSe_1−xTe_x with x = 0.2, 0.3 and 0.5 range from 0.95 to 0.66 W/m K, which is much smaller than that of pure PbSe (2.1-1.3 W/m K) or PbTe (1.4-1.1 W/m K). As a result, the figure of merit for the doped sample can be enhanced. The maximum dimensionless figure of merit ZT of 1.15 was obtained in the sample PbTe_0.5Se_0.5 at 573 K, more than 50% higher than that of pure PbTe prepared in the same condition.     

CuIn1−xAlxS2 thin films prepared by sulfurization of metallic precursors

CuIn_1−xAl_xS₂ thin films (x = 0, 0.09, 0.27, 0.46, 0.64, 0.82 and 1) with thicknesses of approximately 1 μm were formed by the sulfurization of DC sputtered Cu-In-Al precursors. All samples were sulfurized in a graphite container for 90 min at 650 °C in a 150 kPa Ar + S atmosphere. Final films were studied via X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy. It was found that all samples were polycrystalline in nature and their lattice parameters varied slightly nonlinearly from {a = 5.49 Å, c = 11.02 Å} for CuInS₂ to {a = 5.30 Å, c = 10.36 Å} for CuAlS₂. No unwanted phases such as Cu_2−xS or others were observed. Raman were recorded at a room temperature and the most intensive and dominant A₁ phonon frequency varied nonlinearly from 294 cm⁻¹ (CuInS₂) to 314 cm⁻¹ (CuAlS₂).     

Synthesis, structural and microwave dielectric properties of Al2W3−xMoxO12 (x = 0-3) ceramics

Low dielectric ceramics in the Al₂W_3−xMo_xO₁₂ (x = 0-3) system have been prepared through solid state ceramic route. The phase purity of the ceramic compositions has been studied using powder X-ray diffraction (XRD) studies. The microstructure of the sintered ceramics was evaluated by Scanning Electron Microscopy (SEM). The crystal structure of the ceramic compositions as a result of Mo substitution has been studied using Laser Raman spectroscopy. The microwave dielectric properties of the ceramics were studied by Hakki and Coleman post resonator and cavity perturbation techniques. Al₂Mo_xW_3−xO₁₂ (x = 0-3) ceramics exhibited low dielectric constant and relatively high unloaded quality factor. The temperature coefficient of resonant frequency of the compositions is found to be in the range −41 to −72 ppm/°C.     

Crystal structure and dielectric properties of La(Mg1−xZnx)1/2Ti1/2O3 ceramics at microwave frequencies

Ceramics in the system La(Mg_1−xZn_x)_1/2Ti_1/2O₃ with B₂O₃ additions (1 wt.%) have been investigated by the conventional solid-state route. The XRD patterns of the sintered samples (0.3 ≤ x ≤ 1.0) revealed single phase formation with a structure. The unit cell volume slightly increased with increasing Zn content (x). La(Mg_1−xZn_x)_1/2Ti_1/2O₃ were found to form perovskite solid solutions in the whole compositional range. The maximum values of the dielectric constant and the quality factor multiples resonant frequency (Q × f) can be obtained when the La(Mg_0.7Zn_0.3)_1/2Ti_1/2O₃ with 0.5 wt.% B₂O₃ additive were sintered at 1475 °C for 4 h. The temperature coefficient of resonant frequency τ_f (−63 ppm/°C) was measured for x = 0.7.     

Preparation and characterization of La1−xKxFeO3 (x = 0-1) by self-propagating high-temperature synthesis for use as soot combustion catalyst

This paper proposes La_1−xK_xFeO₃ prepared by self-propagating high-temperature synthesis (SHS) as an alternative to platinum catalysts for promoting diesel soot combustion. The catalytic property of eleven products SHSed with different substitution ratios of potassium (x = 0-1) was experimentally evaluated using a thermobalance. In the mass loss curves of the product, T₅₀ was defined as the temperature at which the weight of the reference soot decreases to half its initial weight. The BET specific surface area of SHSed La_1−xK_xFeO₃ depended on x strongly. All the products showed good oxidation catalytic activity. Despite having the smallest surface area (0.11 m²/g) among the obtained products, La_0.9K_0.1FeO₃ (x = 0.1) was found to be the best catalyst with the lowest T₅₀ (442 °C). T₅₀ of La_1−xK_xFeO₃ decreased with increasing x for x > 0.2. The products with x = 0.6 and 0.8 were the second-best catalysts in terms of their T₅₀. Moreover, average apparent activation energy of La_0.9K_0.1FeO₃ (x = 0.1) calculated by Friedman method using TG was as much as 61 kJ/mol lower than that of Pt/Al₂O₃ catalyst. In conclusion, potassium-substituted SHSed La_1−xK_xFeO₃ can be used as an alternative to Pt/Al₂O₃ for soot combustion.     

Microstructure, mechanical and tribological properties of Cr1−xAlxN films deposited by pulsed-closed field unbalanced magnetron sputtering (P-CFUBMS)

Nanocrystallized Cr_1−xAl_xN films with various Al contents (0 to 68 at.%) were deposited by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The effects of aluminum content on the microstructure, mechanical and tribological properties of the Cr_1−xAl_xN films have been investigated. It was found that the hardness and elastic modulus of Cr_1−xAl_xN films increased with increasing Al contents in the films and reached the highest value of 36 GPa and 370 GPa, respectively, at an Al content of 58.5 at.%. Addition of Al beyond 64.0 at.% resulted in a change in crystal structure from B1 cubic to B4 hexagonal phase. The wear resistance improved gradually with the increase of Al in the Cr_1−xAl_xN films. A combination of the abrasive and adhesive wear mechanism was proposed based on the SEM and EDS analysis of the wear track. The steady state dry coefficient of friction measured against a WC ball for the Cr_1−xAl_xN films were in the range of 0.36-0.55, and the wear rate was in the 10^− 6 mm³ N^− 1 m^− 1 range.     

Nanoindentation characteristics of Zr69.5Al7.5 − xGaxCu12Ni11 glasses and their nanocomposites

This work deals with the indentation behavior of Zr_69.5Al_7.5 − xGa_xCu₁₂Ni₁₁ (x = 0, 1.5, 7.5 at.%) alloys. A comparison between their nanohardness and reduced elastic modulus values of the as-synthesized glassy phase with their nanocomposites has been made. The indentation characteristics of a novel Ga substituted glass composition corresponding to x = 7.5 have shown significant improvement in regard to hardness and elastic modulus. The evidence of pile up has been observed in case of as-synthesized glassy ribbons. The load (P) versus depth (h) curves for as-synthesized melt-spun ribbons displayed the presence of displacement burst, which are known as pop-ins. The amount of energy per unit volume required for the shear band formation in glassy state has been estimated based on the pop-ins observed in P-h curve. This seems to decrease with Ga addition. Based on transmission electron microscopic observations of indented glassy specimen, the possibility of nanocrystallization has been ruled out.     

Fabrication and properties of p-type K doped Zn1−xMgxO thin film

A series of K doped Zn_1−xMg_xO thin films have been prepared by pulsed laser deposition (PLD). Hall-effect measurements indicate that the films exhibit stable p-type behavior with duration of at least six months. The band gap of the K doped Zn_1−xMg_xO films undergoes a blueshift due to the Mg incorporation. However, photoluminescence (PL) results reveal that the crystallinity decreased with the increasing of Mg content. The fabricated K doped p-type Zn_0.95Mg_0.05O thin film exhibits good electrical properties, with resistivity of 15.21 Ω cm and hole concentration of 5.54 × 10¹⁸ cm⁻³. Furthermore, a simple ZnO-based p-n heterojunction was prepared by deposition of a K-doped p-type Zn_0.95Mg_0.05O layer on Ga-doped n-type ZnO thin film with low resistivity. The p-n diode heterostructure exhibits typical rectification behavior of p-n junctions.     

High-Q microwave dielectrics in the (Mg1−xZnx)Al2O4 (x = 0-0.1) system

The microwave dielectric properties and the microstructures of (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) ceramic system prepared by the conventional solid-state route were investigated. The forming of spinel-structured (Mg_1−xZn_x)Al₂O₄ (x = 0-0.1) solid solutions was confirmed by the XRD patterns and the measured lattice parameters, which linearly varied from a = b = c = 8.0815 Å for MgAl₂O₄ to a = b = c= 8.0828 Å for (Mg_0.9Zn_0.1)Al₂O₄. By increasing x, the Q × f of (Mg_1−xZn_x)Al₂O₄ can be tremendously boosted from 82,000 GHz at x = 0 to a maximum of 156,000 GHz at x = 0.05. The Zn substitution was effective in reducing the dielectric loss without detrimental effects on the ?_r and τ_f values of the ceramics.     

Calculation of band offsets in Cd1−xXxTe alloys, X = Zn, Mg, Hg and Mn and magnetic effects in CdMnTe

Due to the large variety of properties offered by the telluride binaries CdTe, ZnTe, MgTe, HgTe and MnTe as well as their mixed ternary alloys, an accurate knowledge of their electronic band parameters is crucial. These materials have been extensively studied but, some points bearing on several properties have never previously reported or are still not clear. In this paper, we report results on the conduction and valence band offsets of the pseudo-morphically strained Cd_1−xX_xTe layer on relaxed Cd_1−yX_yTe substrate, X = Zn, Hg, Mg and Mn. Based on the Van Der Walle model, calculations have been performed for the all range of material and substrate 0 ≤ x,y ≤ 1. These discontinuities have not yet calculated for X = Mg, Mn or Hg in the all range 0 ≤ x,y ≤ 1. For the CdMnTe diluted magnetic semiconductor which we focus more interest due to its considerable current interest for applications, calculations have been done without and with correction taking into account magnetic effect of magnesium ions Mn²⁺. It is found that the introduction of only a few percent of Mn into CdTe provides a unique opportunity to combine two important fields in physics, semiconductivity and magnetism. We can take advantage both of possibility of applications in solid-state lasers and exceptional magnetic properties offered by this magnetic diluted semiconductor.This study presents important quantities that are required to model quantum structures and offers a fast and inexpensive way to check device designs and processes.     

Temperature and field induced strain in polycrystalline Ni50Mn35In15−xSix magnetic shape memory Heusler alloys

Magnetic shape memory properties of polycrystalline Ni₅₀Mn₃₅In_15−xSi_x were investigated. A reversible strain of more than 0.4% was observed for x = 0 at a magnetic field H = 5 T that was found to be associated with a field induced reverse martensitic transformation. The strains were found to increase with the substitution of In by Si and strains larger than 1% were observed for x = 2 at H = 5 T. Both the positive and negative strain changes were observed in the vicinity of martensitic transition temperatures. The strain in Ni₅₀Mn₃₅In_15−xSi_x was found to depend on silicon concentration, and on samples texture.     

Corrosion behaviour of dc magnetron sputtered Fe1−xMgx alloy films in 3 wt% NaCl solution

Fe_1−xMg_x alloy films (with x ? 43.4 at.% Mg) were deposited by dc magnetron sputtering onto glass slide substrates. The objective of this study was to characterise the corrosion properties of these alloys in saline solution for application as new friendly environmentally sacrificial coatings in the protection of steel structures. The morphological and structural properties of the alloys were systematically studied prior to electrochemical experiments, and then the degraded surfaces were analysed to determine the composition and nature of corrosion products. Alloys with <25  at.% Mg were single-phase body-centred cubic (bcc) with enlarged lattice parameters, whereas for magnesium contents above 25 at.%, amorphisation occurred. The reactivity of the alloys in saline solution is strongly dependent on the Mg content and the alloy structure. The incorporation of magnesium leads to an open circuit potential shift of the alloy towards more negative values, that confers an attractive interest of these alloys as sacrificial coatings. A transition in corrosion activity is observed at 25 at.% Mg from which the reactivity decreases with the magnesium content increase. The evolution of the alloy corrosion behaviour is discussed in terms of structural and corrosion products evolution versus magnesium content.     

Structural investigation of thin films of Ti1−xAlxN ternary nitrides using Ti K-edge X-ray absorption fine structure

Thin films of Ti_1−xAl_xN nitrides were prepared over a large range of composition (0 ≤ x < 1) on Si substrates using nitrogen reactive magnetron sputtering from composite metallic targets. Ti K-edge X-ray Absorption Spectroscopy experiments were carried for a better understanding of the local structure. The evolution of the intensity of Ti K-edge pre-edge peak gives evidence of the incorporation of Ti in hexagonal lattice of AlN for Al-rich films and in cubic lattice of TiN for Ti-rich films. An attempt to determine their atomic structure by combining X-ray diffraction and Ti K-edge Extended X-ray Absorption Fine Structure is presented. The evolution of the nearest neighbour and next-nearest neighbour distances depending on the composition is presented and discussed together the cubic and hexagonal lattice parameters. A possible contribution of amorphous nitrides is suggested.     

High temperature thermoelectric properties and energy transfer devices of Ca3Co4−xAgxO9 and Ca1−ySmyMnO3

The high temperature oxide thermoelectric materials of p-type Ca₃Co_4−xAg_xO₉ (denoted as p-Co349/Ag_x) and n-type Ca_1−ySm_yMnO₃ (denoted as n-Mn113/Sm_y) were prepared by the self-ignition method combined with a sintering technique. The influence of doping Ag and Sm on the thermoelectric properties of the corresponding materials was evaluated. The figures of merit, ZT, for the p-Co349/Ag_0.2 and n-Mn113/Sm_0.02 materials reached maxima of 0.20 and 0.15 at 973 K, respectively. The performances of thermoelectric devices constructed with the p- and n-type pairs were evaluated in terms of the maximum output power (P_max) and manufacturing factor. The P_max and volume power density for the four-leg devices reached 36.8 mW and 81.9 mW cm⁻³ at ΔT of 523 K, respectively.     

Structural, elastic and electronic properties of Mg(Cu1−xZnx)2 alloys calculated by first-principles

The structural, elastic and electronic properties of Mg(Cu_1−xZn_x)₂ alloys (x = 0, 0.25, 0.5,and 0.75) were investigated by means of first-principle calculations within the framework of density functional theory (DFT). The calculation results demonstrated that the partial substitution of Cu with Zn in MgCu₂ leaded to an increase of lattice constants, and the optimized structural parameters were in very good agreement with the available experimental values. From energetic point of view, it was found that with increase of Zn content the structural stability of Mg(Cu_1−xZn_x)₂ alloys decreased apparently. The single-crystal elastic constants were obtained by computing total energy as a function of strain, and then the bulk modulus B, shear modulus G, Young's modulus Y and Poisson's ratio ν of polycrystalline aggregates were derived. The calculated results showed that among the Mg(Cu_1−xZn_x)₂ alloys, MgCuZn exhibited the largest stiffness, while Mg₂Cu₃Zn showed the best ductility. Finally, the electronic density of states (DOSs) and charge density distribution were further studied and discussed.