Facile microwave assisted combustion synthesis, structural, optical and magnetic properties of La2? xSrxCuO4 (0???x ? 0.5) perovskite nanostructures

Cobalt substituted La2CuO4/LaCoO3 perovskite nanocomposites were prepared using a microwave combustion method. X-ray diffraction analysis showed that Co2+ substitution in La2CuO4 induced the formation of a secondary LaCoO3 phase with rhombohedral structure along with the existing orthorhombic (La2CuO4) structure. The orthorhombic/rhombohedral structured nanocomposites possessed an average crystallite size in the range of 36–46 nm and 21–49 nm, respectively. The Rietveld analysis confirmed the formation of these two phases. The appearance of FT-IR bands around 682 and 512 cm−1 was correlated to the orthorhombic stretching modes while the bands around 580 and 445 cm−1 were associated with the rhombohedral stretching modes thereby confirming the two-phase perovskite system. An optical study revealed two linear regions depicting two band gaps related to the La2CuO4 and LaCoO3 phases. The band gap was found to increase with an increase in the Co2+ doping fraction. Morphological observations using scanning electron microscopy showed intragranular pores and fused grains with distinct grain boundaries. The change in the magnetic properties was associated most probably with the exchange of the A and B sites within the La2CuO4 host lattice because of Co2+ doping, as well as the important phase composition of La2CuO4/LaCoO3 obtained from the ferromagnetic-to-paramagnetic transition. The BET surface area of the pure and doped nanocomposites was found to vary considerably within the range of 12.2–43.7 m2 g−1. The as-fabricated La2CuO4/LaCoO3 perovskite nanocomposites were evaluated for the conversion of glycerol to formic acid in a liquid phase batch reactor under atmospheric conditions. This La3+ based nanocomposite behaves as an efficient bifunctional catalyst with high conversion efficiency and selectivity around 96.5% and 95.1%, respectively.

Co2+ substituted La2CuO4/LaCoO3 perovskite nanocomposites: synthesis, properties and heterogeneous catalytic performance

Through far-infrared studies of La2-xSrxCoU4 single crystals for x = 0.063, 0.07, 0.09, and 0.11, we found that only similar to0.2% of the total holes participated in the nearly dissipationless normal state charge transport and superconductivity. We have also observed characteristic collective modes at omega similar to 18 and 22 cm(-1) due to the bound carriers in an electronic lattice (EL) state, and the free carriers are massively screened by the EL. Our findings lead us to propose a composite picture of the charge system where the free carriers are coupled to and riding on the EL. This unique composite system of charge carriers may provide further insights into the understanding of the cuprate physics.

The composite picture of the charge carriers in La2−xSrxCuO4 (0.063 ≤ x ≤ 0.11) superconductors

Structural, magnetic and catalytic properties of La2-xBaxCuO4 (0 ≤ x ≤ 0.5) perovskite nanoparticles

Structural, optical, and magnetic properties of Ca2+ doped La2CuO4 perovskite nanoparticles

A series of La 2 CuO 4+ δ samples chemically oxidized in NaClO aqueous solution at room temperature with different oxidation time of 2–120 h have been prepared. The X-ray powder diffraction analyses indicate that all the oxidized samples are orthorhombic and single phase, and show an enhanced orthorhombic distortion with the oxidation time, compared with that of the as-prepared sample. The magnetic susceptibility measurements indicate that all the oxidized samples are bulk superconductors with an onset transition temperature at 45 K. The excess oxygen contents of the oxidized samples determined by iodometric titration increase with the oxidation time, which versus the oxidation time obeys the law of the second order exponential decay. The grain size observed by scanning electron microscopy has no obvious changes for the sample before and after oxidation. All the results indicate that NaClO is indeed an efficient oxidizing agent for La 2 CuO 4 .

Structural and superconducting properties of La2CuO4+δ chemically oxidized by NaClO

We fabricated highly textured Y1−xHoxBa2Cu3Oy (x=0, 0.2, 0.4, and 0.6) bulk samples by a ‘‘powder melting process’’ method under identical conditions and investigated their critical current densities and flux pinning behavior with a superconducting quantum interference device magnetometer. The dependence of Jc on the magnetic field, estimated by the Bean model, is studied. The results indicate that Jc drops with the magnetic field according to a power law Jc∝H−n (n<0.5), which implies that the Jc value of these samples is controlled by the flux pinning rather weak links. It is found that Jc and flux pinning can be significantly improved by Ho substitution for Y in Y‐based superconductors. The reduction of the size of Y2BaCuO5 particles, stress‐field pinning, and magnetic pinning created by the Ho addition are considered to be responsible for the increase in Jc and flux pinning.

Critical current density and flux pinning in Ho‐doped melt‐processed YBa2Cu3Oy

Structural features and physical properties in La2CuO4+x materials have been systematically investigated. A short-range-order (SRO) state has been observed at low temperatures for 0.05<x<0.1. Anomalies in physical properties, in particular a superconducting phase segregation, are found to be in connection with the presence of this SRO state. We herein explain this SRO state in terms of intercalated-oxygen ordering, which could yield a local excess-oxygen content of x congruent to1/16 and a local hole concentration of n congruent to1/8.

Short-range-oxygen order and superconducting phase separation in La2CuO4+x

The effect of quenching and preparing procedure on the superconductivity, oxygen content and microstructure of Bi(Pb)-2223 phase has been investigated by means of TEM, TGA and oxygen content and superconductivity measurements. The results show that Tc (0) exhibits a nonlinear change with raising quenching temperature, in the range of 100–400°C, Tc (0) unchangs approximately, in 500–600°C, Tc (0) increases slightly, at 750°C, Tc (0) exhibits a minimum value. The oxygen content is increased and the weak link behavior is improved in the samples quenched at 500–600°C and 800–820°C respectively.

Effect of quenching and preparing procedure on the superconductivity, oxygen-content and microstructure of bi(pb)-2223 phase

The magnetic relaxation has been measured using a SQUID magnetometer for the YBa 2 Cu 2.95 Sn 0.05 O y superconductor, which was prepared by the powder melting process (PMP) method. It is found that the magnetization shows a good linear dependence on lnt in a very large range of temperature (4.5–85K). Moreover, the pinning potential increases with increasing temperature in the Sn-doped sample.

J.Q. Li

Papers

Structural and superconducting properties of La2CuO4+δ chemically oxidized by NaClO

Critical current density and flux pinning in Ho‐doped melt‐processed YBa2Cu3Oy

Short-range-oxygen order and superconducting phase separation in La2CuO4+x

Effect of quenching and preparing procedure on the superconductivity, oxygen-content and microstructure of bi(pb)-2223 phase

Investigation of flux pinning and magnetic relaxation behavior in PMP YBa2Cu2.95Sn0.05Oy sample