Fluctuation-Induced Conductivity of Cu0.5Tl0.5Ba2Ca2Cu2M1O10−δ (M = Si, Sn, Ge) Superconductors

Fluctuation-induced conductivity of Cu_0.5Tl_0.5Ba₂Ca₂Cu₂M₁O_10−δ (M = Si, Sn, Ge) superconductors has been studied from the resistivity vs. temperature data. The logarithmic plots of excess conductivity (Δσ) vs. reduced temperatures [ε=(T−T _c ^mf )/T _c ^mf ] show two crossover temperatures with three exponents. A distinct crossover from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov–Larkin equations has been observed in all the samples. Another crossover from 2D to 0D fluctuations has also been witnessed. FIC data analysis has been found to be quite useful in explaining the superconducting properties of the samples. Si and Sn doped samples have shown almost similar characteristics, while in Ge doped sample diverse behavior is observed.     

Subsolidus Phase Relations in the Systems M2 +O–M2+O–V2O5(M+ = Li, Na, K, Rb, Cs; M2+ = Mg, Ca)

Subsolidus phase relations in the M₂O(M₂CO₃)–MgO–V₂O₅ and M₂O(M₂CO₃)–CaO–V₂O₅ (M = Li, Na, K, Rb, Cs) systems are studied. Twenty mixed vanadates are obtained, of which Rb₂CaV₂O₇, Cs₂CaV₂O₇, LiMg₄(VO₄)₃, RbCaVO₄, and CsCaVO₄ are identified for the first time. Structural data are summarized for all of the mixed vanadates: the space group and lattice parameters are indicated for 14 compounds (for 6 compounds, such data are obtained for the first time), and I and d data are presented for 8 compounds. Partial series of Ca₃(VO₄)₂-based solid solutions with the general formula Ca_{3 – x} M_2x (VO₄)₂ (M = Na, K, Rb, Cs) are identified in the range 0 < x 0.14. Six phase diagrams (M⁺ = Li, Rb, Cs; M²⁺ = Mg, Ca) are investigated and are compared with the phase diagrams of the other ternary systems in question. The key features of the ternary phase diagrams and, hence, the reactivity of the constituent oxides are shown to vary systematically in going from Li₂O to Cs₂O and from MgO to SrO, which is interpreted in terms of the variation in the ionic radius of the alkali and alkaline-earth metals.     

固相法合成La2Ni0.5M0.5O4+δ(M=Co,Cu)材料及电性能

使用金属氧化物La2O3,NiO,CuO和Co2O3作为原料,固相反应法能够合成出具有K2NiF4型结构单一相的、且晶粒尺寸在35～50nm范围的La2Ni0.5M0.5O4 δ(M=Co,Cu)粉料,用XRD、SEM和直流四极探针电导测试法研究了合成La2Ni0.5M0.5O4 δ(M=Co,Cu)粉料的煅烧工艺条件和掺杂元素对电性能的影响以及粉料的颗粒形貌.随着煅烧温度的升高和保温时间的延长,晶粒尺寸在不断长大;合成的粉料在1300℃烧结5h后所有样品的电导率在空气条件下于100～800℃范围内都在增加.掺杂C0或Cu后的材料La2NiO4 δ的电导率均有增加,但掺杂Co后材料电导率要大于掺杂Cu的电导率.为此确定La2Ni0.5M0.5O4 δ(M=Co,Cu)类粉料固相法合成的适宜煅烧条件为1400℃下保温时间14h.     

Giant Magnetoresistance Effect of [bcc-Fe(M)/Cu](M=Co,Ni) Multilayers

1. IlltroductionGiant magnetoresistance (GMR) effect of metallic multilayers has been widely investigated after thefinding by Baibich et al.11], as a new phenomenon tobreak through the memory density in ultra high density magnetic recording, high sensitivity in magnetichead, and so on. Metallic multilsyers of 3d transition elements could be classified into three groups of[bee/bcc], [fee/fccl and [bee/fcc] from the standpointof combination of crystal structure of constituting elements of metal…     

Microstructure Effects on the Superconducting Properties of YBa2Cu3 – x M x O7 – δ (M = Ag, Hg)

The properties of YBa₂Cu_{3 – x} Ag _x O_{7 –} and YBa₂Cu_{3 – x} Hg _x O_{7 –} (0 < x 0.5) solid solutions were studied. The solute concentration is shown to have a significant effect on the superconducting transition temperature, density, and grain size of the solid solutions. The difference in the composition dependences of the properties of the solid solutions is interpreted in terms of the crystal-chemical behavior of the Ag and Hg ions.     

Fluctuation Conductivity of RE1−2x Ca x M x Ba2Cu3O7−δ (RE=Nd,Y and M=Pr,Th) Superconductors

Polycrystalline samples of RE_1?2x Ca _x M _x Ba₂Cu₃O_7?δ with RE=Nd, Y and M=Pr, Th (with 0.0≤x≤0.10), superconductors were prepared by the standard solid-state method. Resistivity was measured as a function of temperature and doping concentration x. Excess conductivity was analyzed using the modified Lawrence-Doniach (LD) expressions. The fluctuation regions, crossover temperatures, coherence lengths, and effective layer thickness were obtained and the values were compared for both samples. For both samples, it was found that with increasing doping, the crossover temperatures were reduced, while the coherence length decreased. The upper critical field and critical current density were increased with increasing doping concentration due to the introduction of disorder and the enhancement of flux pinning by charge neutral doping. Furthermore, the coherence lengths of the Nd-based samples are larger than that for the Y-based samples by a factor 2. It was found that the value of critical current density in Nd(CaPr)-123 is higher than Y(CaTh)-123, from which it is suggested that CaPr doping is more effective than CaTh doping.     

Synthesis and Properties of (Sr1 – xMx)2Nb2O7 (M = Cu, Ni) Solid Solutions

(Sr_{1 – x} M _x )₂Nb₂O₇ (M = Cu, Ni) layered perovskite solid solutions were synthesized, and their stoichiometry ranges were determined. The electrical properties of the solid solutions were compared with those of Sr₂Nb₂O₇.     

Transport and Cu K-XANES Studies of (Hg,Cr)Sr2(Ca,Y)Cu2O6 + δ

The nominal (Hg_0.7Cr_0.3)Sr₂(Ca_0.7Y_0.3)Cu₂O_{6 +} , referred to as (Hg,Cr)-1212, were successfully synthesized at high temperature in partial vacuum. The samples were subsequently annealed in Ar or O₂ annealed at 300°C under ambient pressure. No T _c was observed in any of these samples down to 12 K which is in contrast to high pressure synthesized Y-free (Hg,Cr)-1212 phase where the latter exhibits a superconductivity at 80 K. The divalent state of Cu, as shown by XANES in the as-prepared (Hg,Cr)-1212, is not affected either by Ar or O₂ annealing. Depletion of holes due to trivalent Y substitution at the Ca-site, and a relatively higher 'a' lattice parameter (3.851 Å) are the apparent reasons for the non-superconducting nature of the samples.     

Oxygen Content and Valence of Ru in RuSr2(Gd0.75Ce0.25)2Cu2O10−δ (Ru-1222) Magnetosuperconductor

The valence of Ru was analyzed for two RuSr₂(Gd_0.75Ce_0.25)₂Cu₂O_10– samples with different oxygen contents by Ru L _III-edge x-ray absorption near-edge structure (XANES) spectroscopy. For the sample as-synthesized in 1 atm O₂ the DC magnetization data measured in an applied field of 5 Oe showed a clear branching of the zero-field-cooled (ZFC) and field-cooled (FC) curves around 140 K, an up-turn for both around 100 K and a cusp at 85 K and a diamagnetic transition around 20 K in the ZFC part. A further confirmation for the superconductivity at 28 K was obtained from a resistance vs. temperature measurement. Annealing the as-synthesized sample in 100-atm O₂ atmosphere at 420°C increased the diamagnetic transition temperature from 20 K to 40 K. According to a thermogravimetric analysis, the oxygen content increased accordingly by ca. 0.1 oxygen atoms per formula unit. Quantitative analysis of the XANES spectra using Sr₂RuO₄ (Ru^IV) and Sr₂GdRuO₆ (Ru^V) as reference materials revealed a valence value of +4.74 and +4.81 for Ru in the as-synthesized and the 100-atm O₂-annealed sample, respectively. The obtained result suggests that the valence of Ru in Ru-1222 is affected by the change in oxygen content.     

Effect of MgO Nano-oxide Additions on the Superconductivity and Dielectric Properties of Cu0.25Tl0.75Ba2Ca3Cu4O12?δ Superconducting Phase

The effect of MgO nano-oxide on both superconducting and dielectric properties of polycrystalline (Cu_0.25Tl_0.75)-1234 was studied. The MgO-content varied from x=0.0 up to 1.0 wt% of the sample’s total mass. The volume fraction of the prepared samples (x=0.0, 0.2, 0.6 and 1.0 wt%) was estimated from the room-temperature X-ray powder diffraction patterns. The superconducting transition temperature T _c, calculated from resistivity data, increased from 122 to 136 K as x increased from 0.0 to 0.8 wt% and then it decreased to 117 K for x=1.0 wt%. Also, the dielectric properties of all samples were measured in the frequency range from 100 Hz to 4 MHz at different temperatures from 113 to 300 K. The real part of dielectric constant ε′ was strongly dependent on both temperature and frequency for all x values. The imaginary part of dielectric constant ε″ and loss factor tan δ showed dispersion which shift toward lower frequencies with decreasing temperature. The ac conductivity σ _ac was derived from the admittance and sample dimensions in the same frequency range. It followed the power law σ _ac(ω)∼ω ^−γ with γ≈0.8.     

Fabrication and application of MFe2O4 (M = Zn,Cu) nanoparticles as anodes for Li ion batteries

In this work, MFe₂O₄ (M?=?Zn, Cu) nanoparticles were successfully prepared by a hydrothermal method. The structure, morphology, microstructure, specific surface area and electrochemical properties of the resultant particles were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physical adsorption, charge–discharge test and cyclic voltammetry (CV) method, respectively. The resulting ZnFe₂O₄ and CuFe₂O₄ products were sphere-like and cubic-shaped particles and their average size was about 30–40?nm and 60–70?nm, respectively. The initial discharge capacities of ZnFe₂O₄ and CuFe₂O₄ electrodes reached 1287.5?mAh?g^?1 and 1412.3?mAh?g^?1, respectively, at a current density of 0.2?mA?cm^?2 in a potential range of 0.0–3.0?V. This indicated that Cu is a better counter ion than Zn. The resulting MFe₂O₄ nanoparticles are expected to be a promising candidate of anode materials for Li ion batteries. The reaction mechanism of MFe₂O₄ nanoparticles in Li ion batteries was also discussed based on the CV of Li/MFe₂O₄ cell.     

锂离子电池Li3-xMx N(M:Co,Ni,Cu)系列负极材料研究进展

Li3-xMxN(M:Co,Ni,Cu)具有首次脱锂容量大,良好的充放电可逆性等优点,是制备锂离子电池负极的优良材料.本文介绍了此系列材料的制备方法、结构、特性及其性能.     

Synthesis of new members of Pb-based 1222 superconductors containing sulfur: (Pb0.75S0.25)Sr2(RE1.6Ce0.4)Cu2O z (RE = Sm,Gd, Dy,and Ho)

We have discovered new members of the Pb-based 1222 layered cuprates containing sulfur of (Pb_0.75S_0.25)Sr₂(RE_1.6Ce_0.4)Cu₂O _z with RE = Sm, Gd, Dy, and Ho. All the samples are of almost-single 1222 phase. From the ρ–T and χ–T measurements, they are found to be superconductors after annealing under 125 atm O₂ atmosphere at 400 °C. Among them, the sample with RE = Gd is found to show superconductivity at the highest temperature of 30 K.     

Role of Gd content in Cu(1) and Cu(2) sites on electrical, microstructural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ ceramics

This study deals with the effects of partial Gd³⁺ substitution for the Cu sites on the electrical, microstructural, physical, mechanical and superconducting properties of YBa₂Cu_3?xGd_xO_7?δ ceramic superconductors with x = 0, 0.025, 0.050, 0.100 and 0.150 with the aid of dc resistivity, transport critical current density (J _c ), X-Ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-Ray (EDX), Vickers microhardness (H _v ) and density measurements. The samples studied in this work are prepared by the standard solid-state reaction method. The resistivity (at room temperature), critical (onset and offset) temperature, variation of transition temperature, critical current density, hole-carrier concentration, grain size, phase purity, lattice parameter, texturing, surface morphology, element distribution, density, porosity, crystallinity, Vickers microhardness and elastic modulus (E) values of the samples are obtained and compared with each other. The obtained results show that the room temperature resistivity systematically increases with the increment of the Gd content as a result of the hole filling when the onset (T _c ^onset ) and offset (T _c ^offset ) critical temperatures determined from the resistivity curves are found to decrease from 95.2 to 93.6 K and 92.0 to 83.3 K, respectively, showing the presence of impurities and weak links between the superconducting grains. As for the critical current density measurements, the J _c values decrease from 132 to 34 A/cm² as the Gd doping increases. The XRD results give that although the Gd³⁺ ions substituted tend to occupy both the Cu(1) and Cu(2) sites, the ions are more favorable for the Cu(2) site as a consequence no change of the crystal structure. Besides, the peak intensities belonging to major phase (Y123) decrease monotonously with the increment of the Gd content in the system; however, new peaks belonging to the minor phases start to appear after the doping level of x = 0.0250 beyond which these peaks enhance monotonously, resulting in the decrement of the grain size. Further, the Lotgering indices calculated from the XRD patterns indicate that the texturing of the Y123 grains reduces systematically with the Gd content. According to the SEM investigations, the microstructures of the samples prepared degrade slightly with the content up to the doping level of x = 0.025 after which the morphology suddenly deteriorates due to the appearance of the different phases in the system. EDX measurements show that not only do the elements used for the preparation of the Y123 superconductors with and without Gd content distribute homogeneously but also the level of Cu element rapidly decreases with the increment of the Gd content compared to the other elements, illustrating that the Cu²⁺ ions may partly be substituted by Gd³⁺ ions. Moreover, the porosity analyses for the samples depict that the porosity increases with the Gd content, leading to the degradation of the grain connectivity. We also discuss on the mechanical properties of the samples to examine both the elastic modulus and the strength of connection between superconducting grains.     

Oxidation behaviors of(Hf0.25Zr0.25Ta0.25Nb0.25)C and(Hf0.25Zr0.25Ta0.25Nb0.25)C-SiC at 1300-1500℃

In this work,high-entropy ceramics(Hf_0.25 Zr_0.25Ta_0.25Nb_0.25)C(HZTNC) and HZTNC doped with 20 vol%SiC(HZTNC-SiC) were fabricated by spark plasma sintering.Their oxidation behavior was investigated over the temperature range of 1300-1500℃ for up to 60 min.Both HZTNC and HZTNC-SiC exhibited good oxidation resistance,and their weight change as a function of oxidation time obeyed a parabolic law.Through XRD,microstructure observation,and elemental mapping analysis of the oxide layers,it was found that the formation of Nb₂ Zr₆ O₁₇,Hf₆ Ta₂ O₁₇,and(Ta,Nb)₂ O₅ mixed-oxide layers effectively protected the matrix from further oxidation.Microcracks began to appear on the oxide layer of HZTNC at high temperatures after 60 min of oxidation.However,the addition of SiC in HZTNC suppressed these microcracks at high temperatures due to the active oxidation of SiC.Compared with the oxides formed on HZTNC,the additional formation of Hf(Zr)SiO₄ on HZTNC-SiC could further improve its oxidation resistance over HZTNC ceramics.     

Structural,dielectric, magnetic,and optical properties of Ni0.75Zn0.25Fe2O4–BiFeO3 composites

The magnetoelectric composites of spinel ferrite Ni_0.75Zn_0.25Fe₂O₄ (NZF) and BiFeO₃ (BFO) with general formula xNi_0.75Zn_0.25Fe₂O₄ + (1 ? x)BiFeO₃ (x = 0, 0.10, 0.20, and 0.30) have been prepared via hybrid processing route. Subsequently, the effects of addition of NZF on structural, dielectric, magnetic, magnetoelectric, and optical properties of BFO have been investigated, and significant enhancements have been observed in physical observables such as grain size, dielectric constant, magnetization, and polarization in ferroelectric hysteresis loops. The variation of magnetization with temperature indicates the presence of spin glass behavior along with the ferromagnetic component. The magnetoelectric coupling is found with a value of magnetocapacitance to be 4.6 % for 30 mol% addition of NZF. The optical properties of the composites are also studied using UV–Vis diffuse reflectance spectroscopy, Photoluminescence spectroscopy, and FTIR spectroscopy.     

Influence of Fe/Zn content on the structural,and optical properties of nontoxic and earth-abundant Cu2ZnxFe1 − xSnS4 (x = 0, 0.25, 0.5, 0.75 and 1) compounds

Journal of Materials Science: Materials in Electronics - In this paper, we report the synthesis of multicomponent Cu2ZnxFe1???xSnS4 (CZFTS)...     

LiNi0.75Al0.25O2的制备与性能

LiNi0.75Al0.25O2是很有希望取代LiCoO2的新一代锂离子电池正极材料。采用球形Ni(OH)2和LiNo3、Al(OH)3为原料，空气气氛条件下700℃恒温8h合成了锂离子电池正极材料LiNi0.75Al0.25O2。X衍射分析表明合成的LiNi0.75Al0.25O2粉末结晶良好，具有规整的α—NaFeO2层状结构，扫描电镜分析表明粉末颗粒呈球形，粒径约为7μm。充放电测试表明，合成的LiNi0.75Al0.25O2正极材料具有优良的电化学性能。