Influence of Nano-Ag Addition on Phase Formation and Electrical Properties of (Cu0.5Tl0.5)-1223 Superconducting Phase

Superconducting samples of type (nano-Ag) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ , x=0.0, 0.5, 1.0, 1.5, 2.0 and 3.0 wt.%, were prepared under ambient pressure via a single step solid-state reaction technique at 850 °C. The prepared samples were characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and differential scanning calorimetry (DSC). The electrical properties of the prepared samples were investigated using the electrical resistivity and I–V measurements. The low addition of nano-Ag up to x=1.5 wt.% enhanced the phase formation and improved the superconducting transition temperature T _c , critical current density J _c , and melting temperature. For x>1.5 wt.%, a reverse trend was observed.     

Impact of Mn Substitution at Ru Site in?RuSr2(Eu1.4Ce0.6)Cu2O10?�� Magneto-Superconductor

We report the effect of Mn ion substitution on the structural, superconducting and magnetic properties of polycrystalline Ru_1?x Mn _x Sr₂(Eu_1.4Ce_0.6)Cu₂O_10??? system with x=0.0 to 0.50. All the samples crystallizes with tetragonal structure in I4/mmm space group. RuSr₂(Eu_1.4Ce_0.6)Cu₂O_10??? (EuRu-1222) is a reported magneto-superconductor with magnetic ordering at 100 K and superconductivity occurs at ?40 K. The exact nature of Ru spin magnetic ordering is still being debated and no conclusion has been reached yet. Here, we found the superconducting transition temperature T _c=15 K from the dc magnetization measurements for undoped sample. It is observed that the superconducting transition temperature decreases with the Mn doping at Ru site. DC magnetic susceptibility measurements exhibited ferromagnetic like transition for all the synthesized samples. It was also observed that the net magnetic moment decreases gradually with Mn doping, though not monotonically. It seems that doping of Mn in EuRu-1222 at Ru site enhance the AFM ordering of Ru spins and suppress the FM component. Our results point out possible coupling between superconductivity and magnetism.     

Mechanical and Electrical Properties of (Cu0.5Tl0.5)-1223 Phase Added with Nano-Fe2O3

Superconducting samples of type (Cu_0.5Tl_0.5)-1223 added with nano-Fe₂O₃ (x=0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 wt.%) were prepared by solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE), whereas the Oxygen-content of these samples was obtained using non Rutherford backscattering spectroscopy at 3 MeV proton beam. It was found that the Oxygen-content of (Cu_0.5Tl_0.5)-1223 phase was not affected with the addition of nano-Fe₂O₃. The electrical resistivity measurements showed that the superconducting transition temperature (T _c ) increases up to x=0.2 wt.%, followed by a systematic decrease for x>0.2 wt.%. In addition, room temperature Vickers microhardness (H _v ) measurements were carried out at different applied loads (0.49–2.94 N) to study the performance of the mechanical properties of samples. The experimental results of H _v were analyzed using different models such as elastic, energy dissipation, energy balance and modified energy balance models. It has been found that the energy dissipation model is in a good agreement with the microhardness data.     

Effects of Co doping on microstructure and properties of (K0.5Na0.5)NbO3–LiSbO3–BiFe(1−x)Co x O3 lead-free piezoelectric ceramics

0.998 [(0.95(K_0.5Na_0.5)NbO₃–0.05LiSbO₃]–0.002BiFe_(1?x)Co _x O₃ (KNN–LS–BF_(1?x)C _x ) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The influences of Co content on the phase structure, microstructure, density and related electrical properties were investigated. The results reveal that the substitution of Co significantly improves the sinterability and the electrical properties of KNN–LS–BF_(1?x)C _x ceramics, sintered at a lower temperature of 1,030 °C, compared with that of KNN–LS–BF ceramics. With increasing x from 0 to 0.8, all samples show a pure perovskite structure, but the grain size increases continuously,and the porosity level reaches it’s lowest value at x = 0.2. The density ρ, piezoelectric constant d ₃₃, coupling factor k _p and dielectric constant ε _r increase with x up to 0.2, and then decrease with further increase in x value, but the variation of dielectric loss tan δ is opposite. The density and electrical properties achieve optimal value of ρ = 4.287 g/cm³, d ₃₃ = 276 pC/N, k _p  = 48 %, ε _r  = 1,284 and tan δ = 1.95 %, when x = 0.2. And Tc ≈ 340 °C at all the variation range of Co content.     

Effect of Disorder Induced by Heavy-Ion Irradiation on CeCoIn5 Superconductivity

We present a study of the effect of heavy-ion irradiation on a thinned single crystal of the unconventional heavy fermion superconductor CeCoIn₅. Magnetic susceptibility and low-temperature specific heat results show that the superconducting transition temperature (T _c) changed only 4% with irradiation of 1×10¹² ions/cm², Energy=1 GeV, while the specific heat jump at T _c, ΔC, divided by C _n, where C _n is the normal state specific heat just above T _c, was reduced to 3.6 from ΔC/C _n=4.5 for unirradiated CeCoIn₅. The increase of low-temperature magnetic susceptibility and the saturation in magnetization suggest that the defects induced by heavy-ion irradiation are magnetic in nature, as was seen in the case of neutron irradiation on the heavy fermion superconductors, UBe₁₃ and UPt₃. The non-Fermi liquid behavior of the irradiated sample, based on the temperature dependence of the low temperature magnetic susceptibility, is significantly altered.     

Investigation of the functional properties of Mg x Ni1−x Fe2O4 ceramics

The paper presents a complex study of the effect of Mg substitution on the functional properties of Ni-ferrite ceramics prepared by self-combustion sol–gel method. The sintered ceramics have pure cubic spinel structures with an increase of the lattice parameter and the grain size with Mg content. The electrical properties of Mg _x Ni_1?x Fe₂O₄ (x = 0; 0.17; 0.34; 0.5; 0.66; 1) ceramics have been investigated. The complex impedance spectra suggest a grain boundary contribution in the conduction process and reveal that the real part of impedance and the imaginary component (reactance) increase with increasing the Mg amount. The temperature dependence of dielectric properties shows that the hopping of charge carriers is thermally activated. The resistivity as a function of frequency for different degree of humidity was also investigated. All the investigated samples show a typical ferrimagnetic character with a strong non-linearity, small coercitive field (~50 Oe) and a saturation field of ~1kOe, typical to the investigated Mg _x Ni_1?x Fe₂O₄ ceramics. The Curie temperature determined from magnetic susceptibility versus temperature dependences presents a decrease with the addition of non-magnetic Mg²⁺ ion concentration from 603 °C (for x = 0) to 384 °C (for x = 1).     

Microstructure, dielectric and piezoelectric properties of La-modified Bi0.5(Na0.84K0.16)0.5TiO3 lead-free ceramics

Lead-free ceramics (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ were prepared by a conventional ceramic technique and the effects of La doping and sintering temperature on the microstructure, ferroelectric and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and La³⁺ diffuses into the Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ lattices to form a solid solution with a rhombohedral symmetry. The addition of La leads to the significant change in the grain morphology and size for the (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ and a number of rod grains with the length of 10–50 μm and the diameter of 1–2 μm are observed in the ceramic with x = 0.04 sintered at 1,140 °C for 2 h. However, as sintering temperature increases to 1,160 °C, the rod grains disappears and the uniform and rectangular grains are observed in the ceramics with x = 0.04. As x increases from 0 to 0.06, the coercive field E _c of the ceramics decreases from 4.33 to 2.81 kV/mm and the remanent polarization P _r of the ceramics retains the high values of 25.9–27.7 μm/cm². The depolarization temperature T _d decreases from 154 to 50 °C with x increasing from 0 to 0.10. All the ceramics exhibit the diffusive phase transition at high temperature (280–320 °C). The ceramic with x = 0.04 sintered at 1,150 °C for 2 h exhibit the optimum piezoelectric properties, giving d ₃₃ = 165 pC/N and k _p = 32.9 %. The optimum sintering temperature is 1,150 °C at which the improved piezoelectric properties (d ₃₃ = 165 pC/N and k _p = 32.9 %) are obtained. At the high La³⁺ level (x = 0.10 and 0.12), the ceramics exhibit weak ferroelectricity (P _r = 13.0–21.2 μm/cm²) and thus possess poor piezoelectricity (d ₃₃ = 17–27 pC/N).     

Influence of Ag-doping in La0.5Sr0.5CoO3 on Its Structural and Magnetic Properties

The structural and magnetic properties of the mixed valent cobaltites La_0.5Sr_0.5?x Ag _x CoO₃ (0≤x≤0.15) with perovskite structure have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement shows that all our samples crystallize in the orthorhombic structure with $R\overline{3}c$ space group. Although the unit cell volume remains almost constant, the Co–O bond length and the Co–O–Co bond angle are sensitive to the Ag addition. All our studied samples undergo a paramagnetic-ferromagnetic transition with decreasing temperature. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT of La_0.5Sr_0.5CoO₃ (x=0) sample exhibits thermomagnetic irreversibility indicating frustration and competition of both antiferromagnetic and ferromagnetic interactions. It is suggested that Co³⁺ ions are in the intermediate spin state but Co⁴⁺ ions stay in a mixture of intermediate and high spin states. Ag addition leads to dramatic changes in magnetic properties. An interesting result has been obtained for La_0.5Sr_0.4Ag_0.1CoO₃, where the ZFC and FC curves coincide. For La_0.5Sr_0.35Ag_0.15CoO₃ (x=0.15) sample, the observed thermomagnetic irreversibility is much higher than that observed in x=0 sample. Hysteresis loops were recorded for x=0, 0.05, 0.1, and 0.15. The coercitive field is found to increase with Ag content reaching 0.26 T for x=0.15 whereas the remanent magnetization decreases.     

Structure and electrical properties of Bi0.5Na0.5TiO3-Y0.5Na0.5TiO3-BaTiO3 lead-free piezoelectric ceramics

New (1 – x ? y)Bi_0.5Na_0.5TiO₃-xY_0.5Na_0.5TiO₃-yBaTiO₃ lead-free ceramics have been prepared by a conventional ceramic fabrication technique, and their structure and electrical properties have been studied. A morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.04 < y < 0.10. As compared to pure Bi_0.5Na_0.5TiO₃ ceramic, the partial substitutions of Y³⁺ for Bi³⁺ and Ba²⁺ for (Bi_0.5Na_0.5)²⁺ in the A-sites of Bi_0.5Na_0.5TiO₃ lower effectively the coercive field E _c and increase the remanent polarization P _r of the ceramics. Because of low E _c, large P _r and the MPB, the ceramics with x = 0–0.02 and y = 0.06 exhibit the optimum piezoelectric properties: d ₃₃ = 155–159 pC/N and k _p = 28.8–36.7%. The temperature dependences of dielectric properties of the ceramics show relaxor-like behaviors. The ferroelectric properties at different temperature suggest that the ceramics may contain both the polar and non-polar regions near/above T _d.     

Microstructure and magnetic transition in Cr-substituted Mg–Zn spinel ferrite powders prepared via hydrothermal method

Mg–Zn ferrite powder specimens with the nominal composition Mg_0.5Zn_0.5Cr _x Fe_2?x O₄ (x = 0.0–1.0 with steps of 0.2) were synthesized via hydrothermal method. It is found that all the specimens exhibit a typical spinel structure, and the lattice parameter increases slightly with x, which confirms the substitution of Cr³⁺ for Fe³⁺. The average crystallite size first increases but then decreases with x, which is not the same as the results in previous reports on spinels. The particles in specimens are the aggregate of small nanoscale crystallites, and roughly aggregate more extensively with the increasing Cr content. With the increase of x, the saturation magnetization decreases rapidly, and it becomes more and more difficult for the specimens to magnetize to saturation. The increase of coercivity from 0.6 (x = 0.0) to 32.3 kA m^?1 (x = 1.0) shows a transition from a typical soft magnetic behavior to a hard magnetic behavior with the increase of Cr content, which was not reported before.     

Effect of Ho3+ substitution on magnetic and microwave absorption properties of Sr(ZnZr)0.5Fe12O19 hexagonal ferrite nanoparticles

Sr_1?x Ho _x (ZnZr)_0.5Fe₁₁O₁₉ (x = 0.03, 0.06 and 0.09) hexaferrite nanocrystallites of average sizes in the range of 46–60 nm are synthesized by the citrate sol–gel method. Crystalline structure, morphology, magnetic properties, and microwave absorption properties of powders were studied via X-ray diffraction, field emission scanning electron microscope vibrating sample magnetometer, and vector network analyzer, respectively. The magnetic properties such as saturation magnetization (M _s ) and coercivity (H _c ) were calculated from hysteresis loops. The XRD patterns show that the main phase is M-type strontium hexaferrite without other impurity phases. Microwave absorption properties of hexaferrite (70 wt%)–acrylic resin (30 wt%) composites were measured by the standing-wave-ratio (SWR) method in the range from 12 to 20 GHz. Results showed that substitution of Ho³⁺ ions for Sr²⁺ ions in Sr(ZnZr)_0.5Fe₁₁O₁₉ resonance frequency moves to higher frequency. For samples with x = 0.03, a minimum reflection loss of ?42 dB was obtained at 16.6 GHz for a layer of 1.7 mm in thickness. It was concluded that the prepared composites could be good candidates for electromagnetic compatibility and other practical applications at high frequency.     

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).     

Magnetocaloric study of monovalent-doped manganites Pr0.6Sr0.4−x Na x MnO3 (x = 0–0.2)

A systematic investigation of structural, magnetic, and magnetocaloric properties is reported for a series of monovalent sodium-doped manganites Pr_0.6Sr_0.4?x Na _x MnO₃ (x = 0, 0.05, 0.1, 0.15, and 0.2). Rietveld refinements of the X-ray diffraction patterns show that all powder samples are single-phased and crystallized in the orthorhombic structure with Pnma space group. Magnetic characterization and Arrott plot confirm the second-order phase transition at Curie temperature T _C decreasing from 310 K for x = 0 down to 272 K for x = 0.2. Magnetic entropy change is largest for x = 0 reaching 1.95 J kg^?1 K^?1 at 2 T field. This corresponds to a large relative cooling power of 102 J kg^?1 . Magnetic field sensitivity of magnetic entropy change and relative cooling power are analyzed and discussed.     

Gd Substitution Effects on the Magnetic Properties of the Pr1−x Gd x Co4Si Compounds

The crystal structure and magnetic properties of single phase Pr_1?x Gd _x Co₄Si compounds with x=0,0.2,0.4,0.6,0.8, and 1.0 have been investigated. X-ray analysis reveals that the compounds crystallize as a single phase having the hexagonal CaCu₅-type structure with the space group P6/mmm. The substitution of Gd for Pr causes a linear decrease of the unit-cell parameters a and c, and the unit-cell volume V. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The saturation magnetization at 4.2 K decreases upon the Gd substitution up to x=0.6, and then increases.     

Physical Properties of Mo-Doped Cu(Re0.69−x Mo x Ca0.31)Sr2O6, x=0.1 to 0.6 Cuprate Perovskites

The physical properties of high-pressure synthesized polycrystalline Cu(Re_0.69?x Mo _x Ca_0.31)Sr₂O₆ samples are reported in this article to attract the scientific community. The present system undergoes a structural phase transition from cubic symmetry (for x=0, 0.1) to tetragonal for 0.2≤x≤0.4 and again cubic perovskite structure for x=0.5 and 0.6. The pristine compound (x=0) undergoes a ferromagnetic (ferrimagnetic) transition with high T _c～460 K. Neither the Curie temperature nor the effective magnetic moment is enhanced upon Mo substitution. The mechanism of the suppression of ferromagnetism in the present system is discussed assuming a localized electron system which is reminiscent of W substitution (Balamurugan et al. in J. Appl. Phys. 101:09N501, 2007). The temperature dependence of electrical resistivity, ρ decreases with x=0–0.4 and then increases for x=0.5 and 0.6. Though the suppression of ferromagnetism in the present system is similar to W-substitution, interestingly the former one (Mo) shows different results on structural and transport electrical properties which urge for further studies. The interesting aspect of the present work is for x=0.6, the specific heat data shows significant electronic contribution, whereas the resistivity measurement reveals insulating behavior.     

Effects of copper content on the structural and magnetic properties of spinel (Co,Cu)Fe2O4 ferrites

Spinel Co–Cu ferrites with the nominal composition Co_1?x Cu _x Fe₂O₄ ferrites (x = 0.0–0.4 with steps of 0.1) were prepared by a chemical coprecipitaiton and sintering process, and their structural and magnetic properties were studied by using XRD, TGA–DTA, FTIR, SEM and VSM analyses. All the specimens prepared are single phase after sintering at 900 °C for 5 h, and nearly no change of lattice parameter is found. The study of grain size shows that suitable amount of Cu substitution is favorable for the growth of grains, while too much Cu substitution inhibits the growth of grains instead. Also found is that with the increase of x, the saturation magnetization decreases continuously from 76.6 (x = 0.0) to 59.0 emu/g (x = 0.4), while the coercivity exhibits a first decreasing but then increasing tendency.     

Investigation of Anomalous Magnetic Transition in Pr0.5Sr0.5CoO3

Polycrystalline perovskite cobalt oxides Pr_0.5Sr_0.5CoO₃ were prepared by the sol-gel method. We mainly study the anomalous magnetic transition of Pr_0.5Sr_0.5CoO₃. We report the investigations of polycrystalline samples of the metallic ferromagnetic material Pr_0.5Sr_0.5CoO₃ through measurements of X-ray diffraction, the magnetization, and the resistivity. We found an unusual anomaly around T _A=120 K, much below the ferromagnetic transition (T _C=228 K). Further using the variable temperature X-ray diffraction and electron spin resonance (ESR) measurements, we found that as the temperature goes down, the crystal structure changes obviously at T _A=120 K. We show that this actually results in anomalous magnetic transition.     

Properties of B-site non-stoichiometric (K0.5Na0.5)(Nb0.9Ta0.1)1+x O3 lead-free piezoelectric ceramics

The non-stoichiometric (K_0.5Na_0.5)(Nb_0.9Ta_0.1)_1+x O₃ (x = 0, ±0.005, ±0.010) [KN(NT)_1+x ] lead-free piezoelectric ceramics were prepared by normal sintering. The samples were characterized by X-ray diffraction and scanning electron microscopy. All the KN(NT)_1+x ceramics possess orthorhombic perovskite structure. The grain growth of the ceramics is inhibited and the relative density is improved with increasing x. 0.5 mol% (NT)⁵⁺ excess KN(NT)_1+x ceramic which sintered at 1,120 °C has the highest piezoelectric performances among with other samples. Meanwhile, the (NT)⁵⁺ excess ceramics have better time stability than the (NT)⁵⁺ deficient ones. These results show that the KN(NT)_1+x ceramic with x = 0.005 is a promising lead-free piezoelectric material.     

Phase transition and piezoelectric properties of (1 − x)K0.5Na0.5NbO3–xLiSbO3 ceramics by hydrothermal powders

KNbO₃, NaNbO₃ and LiSbO₃ powders were synthesized by a hydrothermal route have been used to prepare (1 ? x)K_0.5Na_0.5NbO₃–xLiSbO₃ (KNN–LS; x = 0.00–0.08) ceramics. The effects of LiSbO₃ doping on the structures of KNN–LS ceramics have been systematically investigated by X-ray diffraction (XRD) and Rietveld refined XRD patterns. A gradual phase transition from orthogonal to tetragonal with the increase of LiSbO₃ content is demonstrated. Thereinto, the monoclinic phase is identified for the KNN–LS ceramic with the LiSbO₃ content of x = 0.08. Meanwhile, the XRD pattern reveals that the intensity ratio of (200)/(002) crystal face of the ceramic with x = 0.08 was bigger than one, which is different from the tetragonal phase. The tetragonal phase is revealed in the KNN–LS ceramic in the vicinity of x = 0.07, accompanying with relatively higher piezoelectric and ferroelectric properties. Tetragonal phase is beneficial to improve the piezoelectric properties of the KNN–LS ceramics.     

Magnetic and Mössbauer Studies of Ba(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>As<Subscript>2</Subscript> Single Crystals

Magnetization and ⁵⁷Fe Mössbauer effect spectroscopy (MS) studies of Ba(Fe_1?x Ni _x )₂As₂ single crystals (x=0 to 0.054) at temperatures (5 K to 300 K) have been performed. Magnetic measurements show that for BaFe₂As₂ the magnetic moment decreases below T _N=136 K. T _N is suppressed monotonically by Ni doping. On the other hand, for higher x values the magnetic moment increases below T _N. Unexpectedly for x=0.024 (T _N=67 K), the virgin zero-field-cooled (ZFC) curve is higher than that of field-cooled (FC) one below 48 K. The magnetic MS spectra of this sample are composed of a superposition of two subspectra, corresponding to commensurate and incommensurate field distributions. The average magnetic hyperfine field H _eff decreases with T and becomes zero at 80 K. For higher x values, the samples become superconducting at T _C=15.5 and 19 K for x=0.046 and 0.054, respectively. For both samples below T _C, the FC curves are positive (the paramagnetic Meissner effect) up to applied field of H～15 Oe and the susceptibility is inversely proportional to H. The MS spectra below and above T _C are almost identical, indicating that the MS parameters are not sensitive enough to detect the superconducting state. The peculiar phenomena observed are attributed to disorder induced by the presence of Ni atoms in the Fe sublattice.