Pressure Effect and Specific Heat of RBa2Cu3Ox at Distinct Charge Carrier Concentrations: Possible Influence of Stripes

In YBa2Cu3Ox, distinct features are found in the pressure dependence of the transition temperature, dTc/dp, and in DeltaCp*Tc, where DeltaCp is the jump in the specific heat at Tc: dTc/dp becomes zero when DeltaCp*Tc is maximal, whereas dTc/dp has a peak at lower oxygen contents where DeltaCp*Tc vanishes. Substituting Nd for Y and doping with Ca leads to a shift of these specific oxygen contents, since oxygen order and hole doping by Ca influences the hole content nh in the CuO2 planes. Calculating nh from the parabolic Tc(nh) behavior, the features coalesce for all samples at nh=0.11 and nh=0.175, irrespective of substitution and doping. Hence, this behavior seems to reflect an intrinsic property of the CuO2 planes. Analyzing our results we obtain different mechanisms in three doping regions: Tc changes in the optimally doped and overdoped region are mainly caused by charge transfer. In the slightly underdoped region an increasing contribution to dTc/dp is obtained when well ordered CuO chain fragments serve as pinning centers for stripes. This behavior is supported by our results on Zn doped NdBa2Cu3Ox and is responsible for the well known dTc/dp peak observed in YBa2Cu3Ox at x=6.7. Going to a hole content below nh=0.11 our results point to a crossover from an underdoped superconductor to a doped antiferromagnet, changing completely the physics of these materials.Comment: 6 pages, 5 figures Proccedings of the 'Stripes 2000' Conference, Rome (2000

Aspectos físicos e socioeconômicos da bacia hidrográfica do rio Ivinhema.

Aspectos fisicos; Solos; Aspectos socioeconomicos; Aptidao agricola das terras.bitstream/item/65676/1/DOC25-00-ivi.pd

Current Redistribution in a Superconducting Multi-Strand 35 kA DC Cable Demonstrator

High temperature superconductors (HTS) are discussed as energy-efficient solutions for industrial high-current applications beyond 10 kA e.g., bus bar systems in industrial electrolysis plants. In this contribution, the experimental test of a 3.6-meter-long 35 kA DC demonstrator, made from twelve high-current HTS CrossConductor (HTS CroCo) strands in an liquid nitrogen bath at T = 77 K is presented. In this work, a common connector concept of the twelve HTS CroCo strands is proposed. Compared to earlier results without common connector, lead resistances were effectively reduced and current distribution among the individual strands was significantly facilitated. This is confirmed by the observation of increased critical cable current of 37.6 kA compared to 33 kA in previous work without low-resistive common connector. Additionally, the current range, in which all twelve strands reached their critical electric field, was found to be reduced from >7 kA to 2 kA. Results are discussed and assessed with the help of an electric circuit model, from which the solder resistances at the connections could be obtained by fitting. Particular focus was given to the investigation of current redistribution in the demonstrator. Therefore, a heater was installed on one HTS CroCo strand, and activated to raise the temperature on this strand and quench a single strand locally. It is observed that current is redistributed through the common connectors to the other strands

Development and test of a 35 kA - HTS CroCo cable demonstrator

The answer to energy-efficient electric power transfer of high currents in the range of several tens of kA can be given by high temperature superconducting (HTS) cables. BSCCO and MgB2 have been used widely for such cables, reaching maximum currents of about 20 kA. REBCO coated conductors are promising for future HTS cables beyond 20 kA and allow the operation based on subcooled liquid nitrogen. Several cabling concepts based on REBCO tapes were developed world-wide to realize such cables. Using the stacked-Tape concept, a scalable semi-industrial process was developed by KIT, called HTS CrossConductor (HTS CroCo). Key aspects of the conceptual design of high-current HTS cables are discussed and the design of a 35 kA DC cable demonstrator made from HTS CroCo strands is presented. Aspects regarding joints, current redistribution between individual strands and electrical stabilization are highlighted. The performance of this demonstrator cable was tested, reaching the envisaged current