Exploration of new superconductors and functional materials, and fabrication of superconducting tapes and wires of iron pnictides

Al-doped ZnO (AZO) nanoparticles have been prepared using a modified sol–gel technique The as-prepared AZO nanoparticles were annealed at 400 °C, and their morphologies and microstructural characteristics were investigated using transmission electron microscopy (TEM) and x-ray powder diffraction (XRD) analyses Crystallites with an average size of approximately 60–70 nm and ZnO as a primary phase were observed in all samples In addition, smaller nanoparticles (less than 5 nm) with an Al-rich structure covering the surface of larger ZnO crystallites were also noted on the Al-doped samples Chemoresistive devices consisting of a thick layer of AZO nanoparticles on interdigitated alumina substrates have been fabricated, and their electrical and sensing characteristics for carbon monoxide were investigated Al-doping provided a remarkable decrease in the electrical resistance of the sensing layer at the working temperature of the sensors (250–300 °C) The sensors based on Al-doped ZnO exhibited a higher response than the pure ZnO sample, allowing the detection of CO at sub-ppm concentrations in air The enhancement in sensing properties was discussed in terms of the characterization and electrical data

Al-doped ZnO for highly sensitive CO gas sensors

Sol–gel synthesis of 8 nm magnetite (Fe3O4) nanoparticles and their magnetic properties

We have examined the potential of 10 MW superconducting direct drive generators to enter the European offshore wind power market and estimated that the production of about 1200 superconducting turbines until 2030 would correspond to 10% of the EU offshore market. The expected properties of future offshore turbines of 8 and 10 MW have been determined from an up-scaling of an existing 5 MW turbine and the necessary properties of the superconducting drive train are discussed. We have found that the absence of the gear box is the main benefit and the reduced weight and size is secondary. However, the main challenge of the superconducting direct drive technology is to prove that the reliability is superior to the alternative drive trains based on gearboxes or permanent magnets. A strategy of successive testing of superconducting direct drive trains in real wind turbines of 10 kW, 100 kW, 1 MW and 10 MW is suggested to secure the accumulation of reliability experience. Finally, the quantities of high temperature superconducting tape needed for a 10 kW and an extreme high field 10 MW generator are found to be 7.5 km and 1500 km, respectively. A more realistic estimate is 200–300 km of tape per 10 MW generator and it is concluded that the present production capacity of coated conductors must be increased by a factor of 36 by 2020, resulting in a ten times lower price of the tape in order to reach a realistic price level for the superconducting drive train. (Some figures in this article are in colour only in the electronic version)

Superconducting Wind Turbine Generators

Quantum confinement and surface effects (SEs) dramatically modify most solid state phenomena as one approaches the nanometer scale, and superconductivity is no exception. Though we may expect significant modifications from bulk superconducting properties when the system dimensions become smaller than the characteristic length scales for bulk superconductors—such as the coherence length or the penetration depth—it is now established that there is a third length scale which ultimately determines the critical size at which Cooper pairing is destroyed. In quasi-zero-dimensional (0D) superconductors (e.g. nanocrystalline materials, isolated or embedded nanoparticles), one may define a critical particle diameter below which the mean energy level spacing arising from quantum confinement becomes equal to the bulk superconducting energy gap. The so-called Anderson criterion provides a remarkably accurate estimate of the limiting size for the destabilization of superconductivity in nanosystems. This review of size effects in quasi-0D superconductors is organized as follows. A general summary of size effects in nanostructured superconductors (section 1) is followed by a brief overview of their synthesis (section 2) and characterization using a variety of techniques (section 3). Section 4 reviews the size-evolution of important superconducting parameters—the transition temperature, critical fields and critical current—as the Anderson limit is approached from above. We then discuss the effect of thermodynamic fluctuations (section 5), which become significant in confined systems. Improvements in fabrication methods and the increasing feasibility of addressing individual nanoparticles using scanning probe techniques have lately opened up new directions in the study of nanoscale superconductivity. Section 6 reviews both experimental and theoretical aspects of the recently discovered phenomena of ‘parity effect’ and ‘shell effect’ that lead to a strong, non-monotonic size dependence of the superconducting energy gap and associated properties. Finally, we discuss in section 7 the properties of ordered heterostructures (bilayers and multilayers of alternating superconducting and normal phases) and disordered heterostructures (nanocomposites consisting of superconducting and normal phases), which are primarily controlled by the proximity effect.

https://iopscience.iop.org/article/10.1088/0034-4885/77/11/116503/pdf

A review of finite size effects in quasi-zero dimensional superconductors

Nanometer Al2O3 particles were added to (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) precursor powders during the final sintering cycle of a multi-step preparation process. The influence of Al2O3 on the melting temperature, high-Tc (Bi-2223) phase formation, microstructure and transport properties of ceramics was studied by means of DTA, XRD, SEM/EDX, electrical and magnetic measurements. We report that the addition of a small amount of Al2O3 (0.2 wt.%) increased the pellet's critical current density, Jc at 77 K by ∼30% and improved Jc behaviour in applied magnetic field either parallel or perpendicular to the sample wide surface (SWS). The results indicate that the introduction of a proper amount of nano-Al2O3 particles during the final processing of BPSCCO samples can effectively improve the flux pinning ability and has a little detrimental effect on the (Bi,Pb)-2223 formation process.

Addition of nanometer Al2O3 during the final processing of (Bi, Pb)-2223 superconductors

Nano- Al2O3 particle addition effects on Y Ba2Cu3Oy superconducting properties

The effect of nano-size Al 2 O 3 (40 nm) addition on the microstructure and pinning properties of polycrystalline (Bi,Pb)-2223 was analyzed. The Al 2 O 3 content in samples varied from 0.0 to 1.0 wt.% of the total mass of the sample. Phase analysis by X-rays diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS), critical current density dependence on applied magnetic field J c ( B ) and electrical resistivity as a function of temperature ρ ( T ) were carried out to evaluate the relative performance of samples. Using the right amount of Al 2 O 3 addition (0.2 wt.%), the flux pinning ability of (Bi,Pb)-2223 has been enhanced. The pinning force analysis and microstructure observations indicated that the sharp interface between nanometer scale Al-rich particles and the (Bi,Pb)-2223 phase provided effective normal surface pinning centers.

Flux pinning by Al-based nano particles embedded in polycrystalline (Bi,Pb)-2223 superconductors

We report the elaboration of vanadium-doped ZnO nanoparticles prepared by a sol–gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. Vanadium doping concentration of 10 at% has been investigated. The obtained nanopowder was characterised by various techniques such as particle size analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). In the as-prepared state, the powder with an average particle size of 25 nm presents a strong luminescence band in the visible range after thermal treatment at 500 °C in air. The energy position of the obtained PL band depends on the wavelength excitation and presents a blue shift with measurement temperature increase. Different possible attributions of this emission band will be discussed.

M. Ben Salem

Papers

Addition of nanometer Al2O3 during the final processing of (Bi, Pb)-2223 superconductors

Nano- Al2O3 particle addition effects on Y Ba2Cu3Oy superconducting properties

Flux pinning by Al-based nano particles embedded in polycrystalline (Bi,Pb)-2223 superconductors

Synthesis and luminescence properties of vanadium-doped nanosized zinc oxide aerogel

SiO2 nanoparticles addition effect on microstructure and pinning properties in YBa2Cu3Oy