Enhancement of magnetism by tailoring synthesis conditions in electron-doped superconducting nanoparticles.

A study on the effects of sample synthesis conditions on the particle size, structure, and magnetic properties of electron-doped cuprate superconductors of Eu1.85Ce0.15CuO4+α-δ (ECCO) nanoparticles has been carried out using transmission electron microscopy (TEM), X-ray diffraction (XRD) and the superconducting quantum interference device magnetometer (SQUID). The ECCO nanoparticles were prepared through the sol-gel method with various sintering and annealing temperatures. From TEM characterization, the average particle sizes are 87 nm and 103 nm for the sintering temperatures of 700 °C and 900 °C, respectively. The XRD results with structural Rietveld refinement reveal that the lattice constants and bond distance Cu-O change considerably compared to the bulk case. Reducing the particle and crystallite size to below 200 nm causes strong suppression in the superconducting state. From SQUID measurements it is found that none of the samples show superconducting behavior. An upturn in magnetic susceptibility below 10 K is observed in the sample when the crystallite size is in the range of 69 nm to 88 nm, indicating the existence of magnetism. The lower the sintering temperature of the sample synthesis, the higher the effective magnetic moment and Curie temperature. It suggests that the magnetic correlation is more developed in the smaller samples.

Structural Properties and Hopping Conduction in the Normal State of Electron-Doped Superconductor Cuprate Eu2-x Ce x CuO4+α-δ.

Electron-doped superconducting cuprate of Eu2-x Ce x CuO4+α-δ has been studied in the whole doping regime from x = 0.10-0.20 with reducing oxygen content to investigate the relation between the crystal structure and the hopping conduction in the normal state. Parameter of the crystal structure has been extracted from the X-ray diffraction (XRD) measurement while hopping conduction parameters have been obtained from resistivity measurements. The Eu-O bond length decreases with the increasing doping concentration, indicating the successful doping by the partial replacing of Eu3+ with Ce4+. The resistivity increases with decreasing temperature in all measured samples. This is an indication of bad metal-like behavior in the whole regime in the normal state of electron-doped superconducting cuprate of Eu2-x Ce x CuO4+α-δ. The temperature dependence of resistivity was analyzed by the Arrhenius law and the variable range hopping model. It is found that the hopping conduction mechanism more likely follows the variable range hopping rather than the Arrhenius law, indicating that the hopping mechanism occurs in three dimensions. The Cu-O bond length probably plays an important role in decreasing the activation energy. The decreasing value of the activation energy correlates with the increase in the localization radius.

Observation of Cu Spin Fluctuations in High-Tc Cuprate Superconductor Nanoparticles Investigated by Muon Spin Relaxation.

The nano-size effects of high-Tc cuprate superconductor La2-xSrxCuO4 with x = 0.20 are investigated using X-ray diffractometry, Transmission electron microscopy, and muon-spin relaxation (µSR). It is investigated whether an increase in the bond distance of Cu and O atoms in the conducting layer compared to those of the bulk state might affect its physical and magnetic properties. The µSR measurements revealed the slowing down of Cu spin fluctuations in La2-xSrxCuO4 nanoparticles, indicating the development of a magnetic correlation at low temperatures. The magnetic correlation strengthens as the particle size reduces. This significantly differs from those observed in the bulk form, which show a superconducting state below Tc. It is indicated that reducing the particle size of La2-xSrxCuO4 down to nanometer size causes the appearance of magnetism. The magnetism enhances with decreasing particle size.

Highly enhanced electrical properties of lanthanum-silicate-oxide-based SOFC electrolytes with co-doped tin and bismuth in La9.33-x Bi x Si6-y Sn y O26.

Solid oxide fuel cells (SOFCs) are one of the most promising clean energy sources to be developed. However, the operating temperature of SOFCs is currently still very high, ranging between 1073 and 1273 K. Reducing the operating temperature of SOFCs to intermediate temperatures in between 773 and 1073 K without decreasing the conductivity value is a challenging research topic and has received much attention from researchers. The electrolyte is one of the components in SOFCs which has an important role in reducing the operating temperature of the SOFC compared to the other two fuel cell components, namely the anode and cathode. Therefore, an electrolyte that has high conductivity at moderate operating temperature is needed to obtain SOFC with medium operating temperature as well. La9.33Si6O26 (LSO) is a potential electrolyte that has high conductivity at moderate operating temperatures when this material is modified by doping with metal ions. Here, we report a modification of the structure of the LSO by partial substitution of La with Bi3+ ions and Si with Sn4+, which forms La9.33-x Bi x Si6-y Sn y O26 with x = 0.5, 1.0, 1.5, and y = 0.1, 0.3, 0.5, in order to obtain an electrolyte of LSO with high conductivity at moderate operating temperatures. The addition of Bi and Sn as dopants has increased the conductivity of the LSO. Our work indicated highly enhanced electrical properties of La7.83Bi1.5Si5.7Sn0.3O26 at 873 K (1.84 × 10-2 S cm-1) with considerably low activation energy (E a) of 0.80 eV comparing to pristine La9.33Si6O26 (0.08 × 10-2 S cm-1).