The Effect of Silver Substitution in Bi1.7Pb0.3Sr2Ca2?xAgxCu3Oy

The effect of Ag substitution on the properties of high-temperature superconductor Bi_1.7Pb_0.3Sr₂Ca_2−x Ag _x Cu₃O _y system have been investigated. The electrical and structural properties of the samples, prepared by the conventional solid-state reaction method, have been characterized by X-ray diffraction (XRD), electrical resistance and scanning electron microscopy (SEM) studies. XRD analysis reveals a multiphase structure of the samples, whereas SEM micrographs indicate some morphological changes induced by silver addition. It was found that an increase of the amount of Ag₂O addition leads to an enhancement of the critical temperature and the percentage of Bi-2223 phase in the phase mixture.     

Superconductivity of YBa2?xNdxCu3Oy Solid Solution

The solubility of Nd at the Ba sites and the superconductivity of YBa_2–x Nd _x Cu₃O _y were investigated by X-ray powder diffraction and measurements of the electrical resistance and ac susceptibility. The single Re123 phase was obtained for x0.30. The onset transition temperature is insensitive to the Nd content x in the region of x0.40. All are higher than 95 K. The zero resistance transition temperatures , however, exhibits two-step variation with the increase of x. For x0.25, are all above 92 K. The highest of 94 K was obtained for x=0.25. For x0.3 drops sharply to about 84 K. Finally falls to 30 K and is below 10 K for x=0.5. The two-step variation of T _c might be an indication of the existence of two trap levels for holes.     

The Effects of Substitution of Sn for Cu in Bi1.75Pb0.25Sr2CaCu2.3?xSnxSnxOy

The influence of Sn doping on superconductivity in the Bi-based 2212 phase is studied in this paper. For the samples R–T relations and magnetic hysteresis loops were measured. X-ray powder diffraction analysis was also performed. For Bi_1.75Pb_0.25Sr₂CaCu_2.3–x Sn _x O _y , the experimental results show that by adding the proper amount of Sn the superconductivity of the samples can be improved. As x = 0.15, the critical temperature T _c, the critical current density J _c, and the magnetic pinning force density F reach a maximum. At T = 11 K, the critical state parameters H _c1, H _c2, , , and are calculated and compared with the results reported by other researchers. The experimental results also show that the Sn doping is able to speed up the growth of the 2223 phase. In brief, Sn doping is an effective way of improving the superconductivity in Bi-based superconductors.     

AC Response of Cu0.5Tl0.5Ba2Ca2Cu3?xSnxO10?δ Superconductor

We have studied the ac response of Sn doped Cu_0.5Tl_0.5Ba₂Ca₂Cu_3−x Sn _x O_10−δ superconductor samples from their ac-susceptibility measurements under different magnitudes of ac magnetic fields; H _ac=0.4, 4, 16 A/m. The samples with x=0.5 and 1.0 have shown strong flux pinning and intergrain coupling. However, the sample with Sn doping of x=1.5 has shown very poor flux pinning characteristics.     

Optimum Synthesis Temperature of (Cu1?xTlx)Ba2Ca3Cu4O12?δ Superconductor

The effect of synthesis temperature on the superconducting properties of (Cu_1−x Tl _x )Ba₂Ca₃Cu₄O_12−δ (CuTl-1234) samples has been explored. Almost all the superconducting parameters studied in this research work are observed to be suppressed with the increase of synthesis temperature beyond 880 °C, which may be due to impurities caused by the volatility of some constituents such as thallium and oxygen deficiencies as well in the final compound. The Fluctuation Induced Conductivity (FIC) analysis has shown a decrease in the cross-over temperature (T ₀) and the shift of three-dimensional (3D) Aslamasov–Larkin (AL) regions to the lower temperature with the increase of synthesis temperature beyond 880 °C. A direct correlation between the cross-over temperature (T ₀), the zero temperature coherence length {ξ _c (0)}, the zero resistivity critical temperature {T _c (R=0)} as well as carrier concentration has also been observed.     

The effect of Sm substitution on properties of Bi1.6Pb0.4Sr2Ca2? x Sm x Cu3O y superconductors

The effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples have been investigated in terms of X-ray diffraction (XRD), EDXRF (Energy Dispersive X-ray Fluorescent), magnetoresistivity, critical temperature, transport critical current density, and ac susceptibility measurements. The samples were prepared by the conventional solid-state reaction method. XRD patterns are used to calculate lattice parameters and phase ratio of the Bi-2223 samples. The volume fraction was determined from the intensities of Bi-2223 and Bi-2212 peaks. The room temperature XRD patterns of the samples showed the presence of Bi-2223 phase decreases with increasing the Sm content. We estimated the transition temperature of the samples from the resistivity versus temperature measurements in dc magnetic fields up to 0.6 T. We observed that transition temperature, T _c , and transport critical current density, , depend on the Sm substitution. They both decrease with increasing the Sm substitution. We extracted the peak temperature, T _p , and the pinning force density from our previous ac susceptibility measurements. The pinning force density decreased with increasing the Sm content. The possible reasons for the observed decreases in critical temperature and critical current density due to Sm substitution were discussed.     

Study on the Physical and Electrical Properties of Bi2 ? δZnδSr2Ca2Cu3O10 + y Glass-Ceramic Superconductors

We have fabricated a series of glass-ceramic (Bi_{2 –} Zn) Sr₂Ca₂Cu₃O_{10 + y} , where = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, and investigated the effect of Zn ions on the glass formation, crystallization, thermal, electrical, and on the magnetic properties of the BSCCO-2223 superconductor system. The structural symmetry was found to be tetragonal in all the substitution levels. The best electrical performance was obtained from the = 0 sample, the T _c and T _zero was obtained at 110 K and 107 K, respectively. The J _c values of the samples were determined using the magnetization hysteresis and Bean's model. The crystallization kinetics were investigated using nonisothermal models of Augis–Bennett. The calculated activation energy, E _a, of the system was found to be in the range of 258–336 kJ/mol.     

Thermoelectric Power of Deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ Sintered Superconducting Pellets

The thermal variation of the electrical resistivity and thermoelectric power of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_{10 +} pellets subjected to various degrees of deoxygenation is reported. The temperature dependence of the electrical resistivities of deoxygenated samples displays gradual transformation from metallic-like to semiconductor-like features in the normal state. All the samples however, show superconducting transition, but increasing deoxygenation depresses T _C0 from 102 to 45 K. Gross features of the temperature variation of thermoelectric power observed in properly oxygenated (Bi, Pb)-2223 cuprates are retained in all the deoxygenated samples. Our results on electrical resistivity and thermoelectric power in the normal state have been found to be consistent with a two-band model.     

Synthesis, and study of magnetic properties, of Bi1?xCdxFeO3

Ceramic Bi_1−x Cd _x FeO₃ (x = 0.0, 0.05, and 0.1) samples were prepared by a citrate-gel method. The as-prepared compounds were calcined at 600 °C for 3 h to obtain nearly single-phase materials. The crystal structure, examined by X-ray powder diffraction (XRD) and Rietveld analysis, confirmed that the samples crystallize in a rhombohedral (space group, R-3c no. 161) structure. Magnetic measurements were carried out on the resultant powders from 300 to ~2.5 K. Magnetic hysteresis loops showed a significant increase in magnetization as a result of Cd doping in BiFeO₃.     

Structure, Phonon Vibration, and Spin Correlation of LaBa2Cu3?xCoxOy

Polycrystalline samples LaBa₂Cu_3–xCo _x O _y (0 x 1.0) were synthesized by solid state reaction method. The structure, phonon vibration, conduction, and spin correlation were investigated by means of X-ray diffraction, infrared spectra, resistivity, and electron spin resonance. It is found that there are orthorhombic–tetragonal and tetragonal–orthorhombic structural transitions with Co doping, and the conduction behavior changes from metallic to semiconducting. With the increase of Co content, the Cu(1)—O(1) phonon mode around 531 cm^–1 softens, the Cu(2)—O(2) phonon mode around 657 cm^–1 hardens, and the Cu(1)—O(4) mode around 583 cm^–1 is nearly unchanged. The Cu²⁺ spins tend to localize with Co doping. The changes in structure, phonon vibration, and spin correlation with Co doping are analyzed and discussed.     

Effect of Pb Doping on the Superconducting Properties of?(Cu0.5?xPbxTl0.5)Ba2Ca2Cu3O10?δ

The effect of Pb doping on the superconducting properties of (Cu_0.5−x Pb _x Tl_0.5)Ba₂Ca₂Cu₃O_10−δ (x=0.0, 0.15, 0.25, 0.35) samples has been investigated. Lead is doped in Cu_0.5Tl_0.5Ba₂O_4−δ charge reservoir layer and at the CuO₂ planar sites. A multiphase material is achieved with the doping of Pb at the CuO₂ planar sites; however, a predominant single-phase (Cu_0.5−x Pb _x Tl_0.5)Ba₂Ca₂Cu₃O_10−δ (x=0.0, 0.15, 0.25, 0.35) material is synthesized with the doping of Pb at the charge reservoir layers. Formation of multiphase material with the doping of lead at the planar sites showed that its substitution at the planar site is not possible and the formation of PbO₂ planes is less likely. In the samples doped at the charge reservoir layer, the zero critical temperature [T _c (R=0)] is systematically depressed with the increased concentration of lead. The T _c (R=0) and magnitude of the diamagnetism are enhanced after post-annealing the samples in oxygen atmosphere. An apical oxygen mode is observed around 438 cm⁻¹ in undoped samples, which is shifted to 457–461 cm⁻¹ in the Pb-doped samples. This shift in the peak position is most likely associated with the connectivity of apical oxygen atoms with Pb atoms of (Cu_0.5−x Pb _x Tl_0.5)Ba₂O_4−δ (x=0.0, 0.15, 0.25, 0.35) charge reservoir layers. The presence of Pb in the charge reservoir layer and its increased concentration, somehow, stops the flow of mobile carriers to the conducting CuO₂ planes. The decreased density of mobile carriers diminishes the critical temperature and magnitude of diamagnetism in the final compound. The increased oxygen diffusion in the unit cell achieved by post-annealing in oxygen replenishes the concentration of carriers in conducting CuO₂ planes, which increases the T _c (R=0) and the magnitude of diamagnetism. These experiments have shown that the density of mobile carriers plays a vital role in the mechanism of superconductivity and their depressed density suppresses the superconductivity parameters.     

The Influence of Lithium Halides on the Superconducting Properties of YB2Cu3O7?x

The effects of addition to YBa₂Cu₃O_7–x of lithium halides (YBa₂Cu₃O_7–x (LiF) _y , and YBa₂Cu₃O_7–x (LiCl) _y ) on the structural, electric, magnetic, and transport properties are analyzed. Both structural and superconducting properties depend weakly on the lithium content up to y= 0.10. The critical temperature keeps on a value well above 91 K for a small amount of lithium halide (reaching 93.48K. for y= 0.02 in YBa₂Cu₃O_7–x (LiF) _y and 91.30 K in YBa₂Cu₃O_7–x (LiCl) _y ), but for higher concentration of Li it rapidly decreases (81.68K for y= 0.20). The same behavior is exhibited in the lower intragranular critical field. The intragranular critical current density depends on the magnetic field as a power law:j _cB ^–, with a lithium-concentration-dependent . The voltage–current characteristics follow a law typical for granular superconductors, V(I–I _c(B,T)) ^n(B,T). The dependence of the intergranular critical current, I _c, and of the exponent, n, on temperature, magnetic field, and concentration is analyzed.     

Investigation of the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. II: The series LaMn0.25?xCo0.75?xCu2xO3?δ and LaMn0.75?xCo0.25?xCu2xO3?δ

This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ and LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO₃–LaCoO₃–“LaCuO₃”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich series (LaMn_0.25−x Co_0.75−x Cu_2x O_3−δ), the Mn-rich series (LaMn_0.75−x Co_0.25−x Cu_2x O_3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C. The Co-rich series showed higher thermal expansion coefficients (α_max = 19.6 × 10⁻⁶ K⁻¹) and electrical conductivity (σ_max = 730 S/cm at 800 °C) than the Mn-rich series (α_max = 10.6 × 10⁻⁶ K⁻¹, σ_max = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15. I. Arul Raj—on leave from Central Electrochemical Research Institute, Karaikudi, 630006 India.     

Determination of the Glassy Exponent of Melt Textured YBa2Cu3O7?x by Magnetic Relaxation

By magnetic relaxation method we obtained the glassy exponent (T, H) of the melt textured Yba₂Cu₃O_7–x sample. The results have a similar behavior compared with ones using the method of magnetic field sweep, and are compatible with the model of collective pinning theory.     

超导Ag/Bi1.6Pb0.4Sr2Ca2Cu3O10-x复合氧化物摩擦磨损性能

为适应20℃～-200℃ 温度的适用范围,采用固相法制备了Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x超导材料,用摩擦磨损试验机测试了Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x从液氮温度至室温的摩擦学性能。结果表明 : 在室温 20℃下,Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x与对偶件轴承钢盘对摩时,摩擦系数约为0.35,当温度降到超导转变温度以下时(液氮温度-170℃)摩擦系数大幅度降低,Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x超导态摩擦系数为正常态值的一半,实验证明了电子激励对摩擦能量耗散的作用。为改善室温下Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x摩擦学性能,掺杂不同质量分数 Ag作为润滑组元,制备了Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x超导固体润滑复合材料,取得良好耐磨减摩效果。Ag掺杂不影响Ag/Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x复合材料的超导性,在正常载荷和滑动速度下10 wt%Ag/ Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10-x复合材料摩擦系数为0.2~0.3,磨损率为4.57×10-4 mm3·(N·m)-1。     

Preparation and Magnetic Properties of?(La1?xSr1+x)(Mn0.5Co0.5)O4

A series of single phase (La_1−x Sr_1+x ) (Mn_0.5Co_0.5)O₄ (0≤x≤0.40) materials with a tetragonal K₂NiF₄ structure was prepared by a solid state reaction method at 1400 or 1450 °C with a short period of heating time. Powder X-ray diffraction (XRD) and the Rietveld refinement method were employed for the structural analysis. Unit cell a- and c-axes decrease with increasing amount of Sr substitution. A discrepancy between the zero-field-cooled and the field-cooled magnetization is observed in all samples investigated below a characteristic temperature, T ^*, which likely arises from the canted nature of spins or the random freezing of spins. It appears that T ^* decreases with increasing amount of Sr substitution, which is possibly due to the enhancement of chemical pressure induced by Sr and a corresponding increases of the valence of Mn and/or Co.     

Magnetic and Magneto-Transport Measurements of 57Fe-doped SrCoO3 and Sr1?xCdxCoO3 Perovskites

In this article, the magneto-transport features of ⁵⁷Fe isotope (1%) doped SrCoO₃ (referred to as SrCo_0.99 ⁵⁷Fe_0.01O₃) perovskite compound have been investigated. The compound crystallized in cubic symmetry undergoes ferromagnetic transition around ∼270 K. The isothermal magnetization data collected at low temperature (1.8 K) indicates a characteristic of soft ferromagnet with saturation moment, M _s∼1.81 μ _B/Co. Interestingly, the electrical resistivity, ρ(T), measurements indicate semiconducting properties while metallic nature is seen for the pristine compound. The SrCo_0.99 ⁵⁷Fe_0.01O₃ sample shows temperature and field dependence of magnetoresistance, MR, around 1.5%, which is rather smaller than of the pristine perovskite. The second part of the present work reports the attempt to dope Cd on Sr-site in the perovskite structure, Sr_1−x Cd _x CoO₃, under extreme conditions. A minimum amount of about x=0.05, 0.1 is tested for solid solution in the Sr_1−x Cd _x CoO₃ structure. However, the structural data indicate that Cd is not fully doped in the matrix for x=0.05, 0.1 samples; some of the CdO is intact as an impurity and it did not show major impact on the physical properties of the samples. The ρ(T) data reveal metallic nature for both x=0.05 and 0.1 samples with relatively low resistivity at low temperature regions, and they exhibit −MR ∼4% around ∼250 K. For x=0.05 the molar magnetic susceptibility of the sample shows ferromagnetic transition at T _c=244 K, whereas x=0.1 sample exhibits ferromagnetism at T _c=264 K. The effective Bohr magnetron parameter, p _eff, determined for x=0.05 and 0.1 samples is found to be 3.10 μ _B/Co and 3.25 μ _B/Co, respectively, and these data suggest intermediate spin state for Co⁴⁺ ion for both the samples. The M(H) data for both the samples reveal soft ferromagnetism. The M _s of x=0.05 reaches 1.9 μ _B/Co and of x=0.1 reaches 1.86 μ _B/Co at 1.8 K and 70 kOe conditions.     

The Normal State Properties of Y3Ba5Cu8?xZnxO18?δ Superconductor in Bipolaron Model

We report the effect of Zn Substitution on superconducting and normal state properties of new Y-based Y₃Ba₅Cu_8−x Zn _x O_18−δ superconductor. The resistivity of the samples rather shows linear temperature dependence. Two cases of bipolaron model, in presence and absence of thermally excited individual polarons, are used to analyze normal state resistivity. The effect of Zn substitution on carrier localization, transition temperature, boson–boson relaxation time, and extended bosons are discussed.     

Magnetic susceptibility of (Bi2 ? xSbx)Te3 (0 < x < 1) crystals from 2 to 400 K

The magnetic susceptibility (χ) of crystals of (Bi_{2 − x} Sb _x )Te₃ (0 < x < 1) solid solutions has been measured at temperatures from 2 to 400 K. The χ of the crystals containing 10 and 25 mol % Sb₂Te₃ increases with temperature in the range 50 to 220 K, where the Hall coefficient of Bi₂Te₃ increases anomalously. The increase in diamagnetic susceptibility and Hall coefficient with temperature is shown to be caused by a reduction in light-hole concentration, accompanied by a decrease in light-hole effective mass. With increasing Sb₂Te₃ content, the shape of the χ(T) curve changes as a consequence of changes in band structure, which increase the influence of heavy, paramagnetic holes.     

Effect of Nano-Sized ZnO on the Physical Properties of (Cu0.5Tl0.25Pb0.25)Ba2Ca2Cu3O10?δ

High-temperature superconductor phase of (Cu_0.5Tl_0.25Pb_0.25)-1223 was synthesized by solid-state reaction technique and characterized using X-ray powder diffraction (XRD). XRD analysis revealed that the prepared sample was nearly monophase and exhibited tetragonal structure with space group P4/mmm. Nano-zinc-oxide, prepared by Co-precipitation method, was added to the sample. ZnO-concentrations y varied from 0.0 to 2.0 wt.% of the sample’s mass. The prepared samples were investigated through XRD, scanning electron microscope (SEM), energy dispersive X-ray (EDX), particle size analyzer (PSA), differential scanning calorimeter (DSC), electrical resistivity and transport critical current density measurement. X-ray data analysis showed that the nano-Zn addition does not affect the tetragonal structure of (Cu_0.5Tl_0.25Pb_0.25)-1223 phase, whereas the lattice parameters showed an insignificant variation. The results of the superconducting transition temperature, the transport critical current density and melting point of the prepared samples were found to depend on nano-ZnO concentrations.