Development of novel CoCu0.5FeNiVTix (x = 0, 0.5, 1, 1.5, 2) high-entropy alloys

CoCu_0.5FeNiVTi_x (x?=?0, 0.5, 1, 1.5, 2) high-entropy alloys (HEAs) were prepared using vacuum arc melting. The microstructures, crystal structures, hardness, compressive properties and wear resistances of the alloys were studied. The alloys always contained face-centred cubic (FCC) and body-centred cubic (BCC) solid solution regardless of the increase in Ti content. The microstructure of alloys exhibited typical dendritic characteristics, which were more and more unapparent with the increase in the Ti content. The alloys with a high content of Ti had a high compressive strength and low ductility. Owing to the formation of nano-precipitates and BCC as the major phase, the CoCu_0.5FeNiVTi₁ alloy exhibited the highest compressive strength of 2747?MPa and a plastic strain limit of 7.4%. As the content of Ti was increased, the wear resistance of CoCu_0.5FeNiVTi_x alloys displayed a rapid increase and reached the highest value when x?=?1, and finally decreased. Because of the large volume fraction of BCC, the CoCu_0.5FeNiVTi₁ alloy exhibited high hardness so exhibiting the best wear resistance. Adhesive wear and abrasive wear dominated the wear behaviour of CoCu_0.5FeNiVTi_x alloys during sliding against SUJ2 steel.     

The Effects of Doping on Crystal Structure, Magnetic and Microwave Properties of SrFe12−2x La x (Mn0.5Zr0.5) x O19 Nanoparticles

M-type hexagonal ferrite powders, SrFe_12?2x La _x (Mn_0.5Zr_0.5) _x O₁₉ (x=0.0, 0.2, 0.4, 0.6, 0.8), have been synthesized by the coprecipitation method. The X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer and vector network analyzer all were used to characterize the structure of the samples, their magnetic and microwave properties. The value of the saturation magnetization increased up to x=0.2 and then slowly decreased with increasing doping. A decreasing trend was observed in the value of coercivity with increasing substitution degree, and its value reached a minimum of 2420 Oe for x=0.6 and then increased with further increasing x. The relative complex permittivity and permeability of the composite powders were investigated in the X-band frequency range (8.2–12.4 GHz).     

Synthesis, Characterization and Magnetoresistance Studies of Tl0.5Pb0.5Sr1.6Ba0.4CaCu2?x Ru x O7?δ Superconductor

Bulk superconducting samples of type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ , (Tl,Pb)/Sr-1212, with 0.0≤x≤0.525 were synthesized by the conventional one-step solid-state reaction technique via a short time, using SrO₂ instead of SrCO₃. X-ray powder diffraction XRD, scanning electron microscope SEM and the electrical resistivity measurements at different applied dc magnetic fields (0.0–4.4 kG) were performed in order to investigate the effect of Ru⁴⁺ ions substitution on (Tl,Pb)/Sr-1212 phase. Enhancement of the phase formation, the superconducting transition temperature T _c and the hole carriers concentration P was observed up to x=0.075, and they decreased for further increase in x. The magnetoresistance data of these samples were analyzed within the thermally activated flux creep TAFC model and the Ambegaokar and Halperin AH theory. The derived flux pinning energy U, the critical current density J _c (0) and the upper critical magnetic field B _c2(0) enhanced up to x=0.075, beyond which they decreased for further increase in Ru-content. The coherence length at 0 K ζ(0) decreased up to x=0.075 and increased with x>0.075. In addition, we reported a comparison between the effect of Ru substitution on the physical properties for Gd-123, (Bi,Pb)-2223 and (Tl,Pb)/Sr-1212 phases.     

Effect of Te Substitution on (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7 (x=0.0 to 0.5) Superconductor

The (Tl_0.5Pb_0.5)Sr₂(Ca_1?x Te _x )Cu₂O_7??? (Tl-1212) superconductor for x=0.0 to 0.5 has been prepared and studied by a powder X-ray diffraction method, electrical resistance and AC susceptibility measurements. Most of the samples showed Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Te substitution (x??0.3) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature ( $T_{\mathrm{c\ onset}}$ ) between 92 and 97 K. Our results indicated the combined effects of Te substitution, heating temperature and heating time on the formation and optimization of the (Tl_0.5Pb_0.5)Sr₂(Ca_1?x Te _x )Cu₂O₇ superconductor.     

SrMO3—x（M=Ti,V,Cr,Mn,Fe,Co,Ni,0≤x≤0.5）氧化物的结构及其…

本文总结了国内外对ＳｒＭＯ３－ｘ（Ｍ＝Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ，０≤ｘ≤０．５）氧化物的结构及其电行为的研究，并分析了晶体场效应对这类钙钛矿化合物结构和电性质的影响。     

Microstructure and piezoelectric properties of lead-free 0.95(Na0.5K0.5)NbO3–0.05(Bi0.5K0.5)Zr1−x Ti x O3 ceramics

0.95(Na_0.5K_0.5)NbO₃–0.05(Bi_0.5K_0.5)Zr_1?x Ti _x O₃ (abbreviated as KNN–BKZT _x ) ceramics were prepared by the conventional solid state method, and the effect of the Ti content on the surface morphology, crystalline structure, and electrical properties of KNN–BKZT _x ceramics were mainly investigated. With the increase of Ti content, the temperature of the orthorhombic–tetragonal (O–T) phases transitions shifted to lower temperatures, and the O–T phase boundary of KNN–BKZT _x ceramics was identified in the composition with 0 ≤ x ≤ 0.3 at room temperature. It was considered that the piezoelectric properties of the ceramics were enhanced significantly owing to the more possible polarization states resulting from the coexistence of two phases. The ceramic with x = 0.2 exhibited optimum properties: d ₃₃ = 260 pC/N, k _p = 0.38, and T _C = 323 °C.     

Diamagnetic and Electrical Properties of Si x Mo2S3−x (x=0.1, 0.2, 0.33, 0.5) and A0.1Mo2S3−x (A=C, B, and Ru)

Mo₂S₃ doped with Si, C, B, and Ru, is identified to bear the same crystalline structure P2₁/m as that of Mo₂S₃ through XRD analysis. Diamagnetic transitions with χ _m ～10^?4 emu/g?Oe at temperature ranging from 2 K to 6 K were observed in the doped samples of Si _x Mo₂S_3?x (x=0.1, 0.2, 0.33, 0.5). And both of the x=0.2 and 0.5 samples were found to have double diamagnetic transitions with higher T _c at the same temperature of 6.01 K, while Si _x Mo₂S_3?x of x=0.33 displayed an extra ferromagnetic-like response at 63 K. The corresponding transition in resistivity of Si _x Mo₂S_3?x with x=0.1 was noticed to show a mild drop with less than 10 % of its original transition values as measured down to 2 K. But a superconducting-like magnetic field dependence on the phase transition of resistivity was also noted. Its diamagnetic signals were greatly reduced when the applied magnetic fields were raised to 10³ Oes. In the doped samples of A_0.1Mo₂S_2.9 (A=C, B, and Ru), the phase transition in resistivity at 4.08 K, 4.62 K, and 4.35 K, respectively, exhibited similar fashion as that in the case of Si_0.1Mo₂S_2.9.     

Glass-free LTCC microwave ceramic-Ca1−x(La0.5Na0.5)xWO4

The structure and microstructure of the Ca_1?x(La_0.5Na_0.5)_xWO₄ (0.1 ≤ x ≤ 1.0) ceramics were investigated using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) method. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 10–14 GHz. Continuous solid solutions Ca_1?x(La_0.5Na_0.5)_xWO₄ (0.1 ≤ x ≤ 1.0) with Scheelite structure (space group: I4₁/a) could be densified at 850 °C/2 h. The dielectric permittivity increased slightly with the increase in substitution amount. The Q × f value decreased with the increase of x up to x = 0.5, and then increased with further increase of x. The Q × f value increased when the sintering temperature increased from 850 to 950 °C for the x < 0.5 compositions, whereas it decreased with the increase in sintering temperature for the x > 0.5 compositions. The τ _f value changed a little with the variation of x. All samples exhibited negative τ _f values. Addition of 30 mol% TiO₂ to the x = 0.9 composition improved the τ _f to ?9.3 ppm/°C with ε_r = 14.4 and Q × f = 14,255 GHz after sintering at 850 °C/2 h. The chemical compatibility of Ca_0.1(La_0.5Na_0.5)_0.9WO₄ + 30 mol% TiO₂ composite with silver (Ag) powders was also investigated. The composite showed inert behavior with Ag when cofired at 875 °C for 2 h. However small amount of Na_0.86WO₃ impurity phase was detected in the co-fired specimen.     

(1 − x)CaTiO3–x(Li0.5Nd0.5)TiO3 for ultra-small dielectrically loaded antennas

Microwave (MW) dielectric ceramics based on the solid solution (1 ? x)CaTiO₃–x(Li_0.5Nd_0.5)TiO₃ (0.25 ≤ x ≤ 1.0) were prepared by conventional solid-state synthesis using the mixed oxide route. Compositions closest to zero τ_f (+65 ppm/°C) were obtained at x = 0.8 where ε_r = 110 and the microwave quality factor, Qf ₀ ? 2600 GHz for samples sintered at 1300 °C. To reduce the sintering temperature and compensate for any Li₂O loss during fabrication, ≤0.5 wt% 0.5Li₂O–0.5B₂O₃ was added as a sintering aid in the form of raw oxides (LBR) and also as a pre-reacted glass (LBG). 0.5 wt% LBR was the most effective, reducing the temperature to achieve optimum density by ~50 °C with no significant deterioration of microwave properties (ε_r = 115, τ_f = +65 ppm/°C and Qf ₀ ? 2500 GHz). The high permittivity and relatively low sintering temperatures (1250 °C) are ideal for the development of low cost ultra-small dielectric loaded antenna, assuming the system can be tuned closer to zero by fractionally increasing x.     

Synthesis of Cr x Ti1−2x Nb x O2O20≤x≤0.5 rutile solid solutions from alkoxides

In this study, Cr _x Ti_1–2x Nb _x O₂ (0 x 0.5) rutile solid solutions have been synthesized from gels built from hydrolysis-condensation of Cr (III) acetylacetonate, NbCl₅ and Ti (IV) isopropoxide mixture (polymeric gel). Characterization of these solid solutions was carried out by X-ray diffraction, ultraviolet-visible and infrared spectroscopy, differential thermal and thermogravimetric analysis and CIELAB (Commission Internationale del'Eclairage L^*a^*b^*) parameter measurements. The results obtained by the polymeric gel method were compared with those obtained by traditional ceramic synthesis. This comparison reveals some differences with regard to synthesis temperatures and reaction mechanisms. The formation of Cr _x Ti_1–2x Nb _x O₂ (0 x 0.5) rutile solid solutions by the ceramic method requires temperatures of about 1200°C and soaking times of several days. These solid solutions are synthesized at 1000°C in 24 h by the polymeric gel method. In ceramic synthesis, the CrNbO₄ compound with rutile structure appears as an intermediate compound in the formation of rutile solid solutions. In polymeric gel synthesis, however, the CrNbO₄ rutile compound was not detected in the samples.     

The thermal conductivity and Lorenz function of the tin-lead alloy system Sn x Pb1 − x (x = 0.85, 0.7 0.5 0.3)

The thermal conductivity and electrical resistivity of the tin-lead alloy system Sn _x Pb_{1 – x} (x = 0.85, 0.7 0.5 0.3) were measured in the temperature range 7–300 K. The thermal conductivity was analyzed at temperature T 20K, assuming 1//T+Tⁿ, where , , and n are constants. The analysis shows that n < 2, and not n 2, which would be expected for a normal pure metal. The electrical resistivities could be represented by a T ⁵ relation for temperatures up to about 60 K. The characteristic temperature _R appears to decrease with increasing weight percent of lead. The total Lorenz functions were high, indicating the presence of phonon conductivity. The phonon conductivity _g appears to vary with T, and can be represented by _g=a/Tⁿ (a > 0) and n2.Work supported by the Universiti Sains Malaysia.     

Structural properties of nickel manganite Ni x Mn3−x O4 with 0.5 ⩽x ⩽ 1

Single-phase nickel manganite spinels, Ni _x Mn_3–x O₄, with 0.5 x 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni²⁺ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni²⁺ ions (forx>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni²⁺ in A sites =P = – 82.1x ²+192.4x–81.5 and thus the general formula for cation distribution is

Synthesis and electrical properties of (BaTiO3)1 ?x (K0.5Bi0.5TiO3) x solid solutions

(BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO₃ presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K_0.5Bi_0.5TiO₃ content on the microstructure of the (BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions.     

Relaxor Behavior of Pb[(Mg0.5W0.5 )1 – x Ti x ]1 – y Sn y O3 Ceramics

The dielectric and ferroelectric properties of Pb[(Mg_0.5W_0.5)_{1 – x} Ti _x ]_{1 – y} Sn _y O₃ (x = 0.4–0.5, y = 0–0.15) solid solutions are studied. The results are used to elucidate the origin of the relaxor state developing in a temperature range between the para- and ferroelectric phases.     

Co0.5Mn0.5La x Fe 2−x O4 Magnetic Particles: Preparation and Kinetics Research of Thermal Transformationof the Precursor

Co_0.5Mn_0.5La _x Fe_2?x O₄ precursor was synthesized by solid-state reaction at low temperatures using CoSO₄ ?7H₂O, MnSO₄ ?H₂O, FeSO₄ ?7H₂O, La(NO ₃)₃ ?6H₂O, and Na₂ CO ₃ ?10H₂O as raw materials. Co_0.5Mn_0.5La _x Fe_2?x O₄ was obtained by calcining carbonates precursor in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized Co_0.5Mn_0.5La _x Fe _2?x O₄ with a cubic structure was obtained when the precursor was calcined at 700 °C in air for 2 h. The specific saturation magnetizations and coercivity of Co_0.5Mn_0.5La _x Fe_2?x O₄ depend on the calcination temperature and composition. The thermal transformation of Co_0.5Mn_0.5CO₃–Fe₂O₃?0.967H₂O from 700 °C in air presented two steps. The values of the activation energies associated with the thermal transformation of Mn_0.5Co_0.5CO₃–Fe₂O₃?0.967H₂O were determined based on the Kissinger–Akahira–Sunose (KAS) equation     

Magnetically Recyclable Spinel Mn x Ni1−x Fe2 O 4 (x= 0.0–0.5) Nano-photocatalysts: Structural,Morphological and Opto-magnetic Properties

Manganese doped nickel ferrite (Mn _x Ni_1?x Fe₂ O ₄: x = 0.0–0.5) spinel nanoparticles (NPs) were successfully prepared by a facile microwave combustion method (MCM) using urea as the fuel. The prepared samples were characterized by different techniques. Powder X-ray diffraction (XRD) analysis was confirmed the formation of a single-phase NiFe₂ O ₄ spinel structure. The average crystallite sizes of the samples were in the range of 11.49 to 17.24 nm, which was confirmed by Sherrer’s formula. The morphology of the samples showed a nanoparticle-like structure with smaller agglomeration, which was confirmed by high-resolution scanning electron microscopy (HR-SEM). The particle size diameter ranges from 15 to 20 nm, which was confirmed by high-resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis confirmed the elemental composition, which was also evidence for the formation of single pure phase. Selected area electron diffraction (SAED) analysis showed well crystalline nature. UV-visible diffuse reflectance spectra (DRS) and photoluminescence (PL) spectrum analysis was used to calculate the optical band gap, and the values are slightly increased (2.02 to 2.42 eV) with increasing the Mn-dopant, due to the decreasing of particle size, which may be due to the quantum confinement effect. Magnetic properties of the samples were analyzed by vibrating sample magnetometer (VSM) technique, which showed the magnetization (M _s ) value of the samples are increased with increasing Mn content and reach a maximum value of 67.82 emu/g for Mn_0.5Ni_0.5Fe₂ O ₄ sample. Photo-catalytic activity of the samples was measured and showed the photocatalytic degradation (PCD) of methylene blue dye with good results. The catalyst was magnetically recycled and reused five consecutive cycles and showed good reproducibility without change of catalytic activity.     

New Pb-Based 1222 Cuprates, (Pb0.5B0.5)Sr2(RE2−x−y Ce x Sr y )Cu2O z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y)

New Pb-based layered cuprates with the 1222 structure have been synthesized in the (Pb_0.5B_0.5)Sr₂ (RE_2−x−y Ce _x Sr _y )Cu₂O _z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single-phase samples in the systems can be obtained for a nominal composition of x=0.7 and y=0.1. The crystal structure of the samples has a tetragonal symmetry, the lattice parameters of a and c are increasing with increasing the ionic radius of RE element. Despite treatment under high O₂ pressure of 100 atm, the samples are semiconductors with the transport process characteristic of three-dimensional variable range hopping conduction.     

Fluctuation Induced Conductivity in Hg-Doped (Cu0.5Tl0.5?x Hg x )Ba2Ca3 Cu 4O12?δ Superconductor

The fluctuation induced conductivity (FIC) analysis on resistivity data of the Hg-doped (Cu_0.5Tl_0.5−x Hg _x )Ba₂Ca₃Cu₄O_12−δ (x=0, 0.15, 0.25, 0.35) superconductor has been carried out in the light of the Aslamazov–Larken (AL) theory. The superconducting properties have been improved with Hg-doping (up to x=0.25) at Tl sites in the Cu_0.5Tl_0.5Ba₂O_4−y charge reservoir layer. These samples are also post-annealed in oxygen to improve intergrain connectivity and to optimize the carriers’ density in CuO₂ planes. The results of FIC analysis have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in the order parameters. It has been observed that there is an increase in the cross-over temperature (T _o) as well as in zero resistivity critical temperature {T _c(0)} with Hg-doping. These properties have been further improved after post-annealing in oxygen, which may be due to improved inter-grain coupling and optimization of mobile carriers in CuO₂ planes. A direct correlation between T _o, T _c(0) as well as zero temperature coherence length ξ _c(0) has been observed.     

Composition-dependent structural, optical and electrical properties of In x Ga1−x N (0.5 ≤ x ≤ 0.93) thin films grown by modified activated reactive evaporation

In this report, we have studied the compositional dependence of structural, optical and electrical properties of polycrystalline In _x Ga_1?x N thin films grown by modified activated reactive evaporation. The growth was monitored by optical emission spectroscopy. The thickness of the films was in the range ~600–800 nm. The phase, crystallinity and composition of the films were determined by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analysis. The surface morphology was studied by atomic force microscopy. The band gaps of these films obtained from transmittance and photoluminescence measurements were found to vary from 1.88 to 3.22 eV. All the films show n-type conductivity. The carrier concentration was found to be decreasing with increase in gallium incorporation which is in good agreement with the free carrier absorption observed in transmittance spectra.     

AC Potential-Dependent Concentration Variation and Domain Wall Pinning in Co1−x Zn x (x=0.4−0.5) Nanorods

The Co_1?x Zn _x (x=0.4?0.5) nanorods were synthesized via an AC electrochemical deposition method into anodized aluminum oxide (AAO) templates at different voltages ranging from 10 to 18 V, and nanorods of varying concentrations of Co and Zn were obtained. The characterization tools were used to examine different aspects of nanorods, e.g., shape, size, morphology, chemical composition, and magnetic behavior. Scanning electron microscope (SEM) images show that CoZn nanorods have length L=1μm and diameter d=50 nm. The grain size was calculated to be 25.4 nm using an X-ray diffraction (XRD) technique. The XRD also shows some other phases of ZnCoO. The M?H loops measured by a vibrating sample magnetometer (VSM) at room temperature show pure ferromagnetic behavior at all AC potentials. The nanorods show magnetic isotropic behavior due to strong magnetic interactions and presence of random nanorods. The potential-dependent coercivity H _c and saturation magnetization M _s show a non-linear curve which is explained on the basis of magnetic islands and domain wall pinning. This study is useful to tune the magnetic properties of nanorods by a simple and low-cost technique.