Anders Christian Wulff

Comparing superconducting and permanent magnets for magnetic refrigeration

We compare the cost of a high temperature superconducting (SC) tape-based solenoid with a permanent magnet (PM) Halbach cylinder for magnetic refrigeration. Assuming a five liter active magnetic regenerator volume, the price of each type of magnet is determined as a function of aspect ratio of the regenerator and desired internal magnetic field. It is shown that to produce a 1 T internal field in the regenerator a permanent magnet of hundreds of kilograms is needed or an area of superconducting tape of tens of square meters. The cost of cooling the SC solenoid is shown to be a small fraction of the cost of the SC tape. Assuming a cost of the SC tape of 6000

Comparison Study of YBa2Cu3O7-x Films Deposited by Using Various Carboxylate Solutions

/m2 and a price of the permanent magnet of 100

Investigation of CeO 2 Buffer Layer Effects on the Voltage Response of YBCO Transition-Edge Bolometers

/kg, the superconducting solenoid is shown to be a factor of 0.3-3 times more expensive than the permanent magnet, for a desired field from 0.5-1.75 T and the geometrical aspect ratio of the regenerator. This factor decreases for increasing field strength, indicating that the superconducting solenoid could be suitable for high field, large cooling power applications.

Superconducting Dy1-x(Gd,Yb)xBa2Cu3O7-δ thin films made by Chemical Solution Deposition

In this work, four fluorine-free solutions based on various carboxylates (propionates, butyrates, valerates, and hexanoates, respectively) were prepared and used for deposition of YBCO films on LaAlO3 single-crystal substrates, in order to further understand the role of precursors on properties of the final films. After the same pyrolysis and sintering processes, the films from propionates and butyrates show pure YBCO phase and were epitaxially grown, as determined by X-ray diffractometer analysis. There are clear differences in morphologies of these four films, i.e., the films from propionates and butyrates exhibit platelike grains without distinct grain boundaries, while almost randomly orientated grains were observed on the surface of the other two films. As a result, we noticed significant discrepancies on their superconducting performance. The films from propionates and butyrates give Jc values (at 77 K, self-field) of 2.1 MA/cm2 and 1.3 MA/cm2, respectively, while no superconducting transition above 70 K was observed in the other two films. A relatively larger amount of carbonaceous residue left as a by-product after decomposition of carboxylates with longer ligands, particularly under fast pyrolysis and sintering processes, could be one of the explanations of the poor superconductivity in the films from the valerateand hexanoate-based precursors.

Investigation of a Spinel‐forming Cu‐Mn Foam as an Oxygen Electrode Contact Material in a Solid Oxide Cell Single Repeating Unit

The effect on the thermal parameters of superconducting transition-edge bolometers produced on a single crystalline SrTiO3 (STO) substrate with and without a CeO2 buffer layer was investigated. Metal-organic deposition was used to deposit the 20-nm CeO2 buffer layer, whereas RF magnetron sputtering was applied to fabricate 150-nm-thick superconducting YBa2Cu3O7-δ (YBCO) thin film. The critical transition temperature for both of the YBCO films was 90 K, and the transition width was ~1.9 K. The bolometers fabricated from these samples were characterized with respect to the voltage phase and amplitude responses, and the results were compared with that of simulations conducted by applying a one-dimensional thermophysical model. It was observed that adding the buffer layer to the structure of the bolometer results in an increased response at higher modulation frequencies. Results from simulations made by fitting the thermal parameters in the model with and without an additional CeO2 layer were found to be in agreement with the experimental observations.

Superconducting

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

\text{Dy}_{1-x}(\text{Gd},\text{Yb})_{x}\text{Ba}_{2}\text{Cu}_{3}\text{O}_{7-\delta}

A critical issue in state-of-the-art solid oxide cell stacks is the contacting of the oxygen electrode. The commonly used ceramic contact layers are applied in a green state and cannot be sintered properly, due to compliance limitations arising from other stack components like sealing glasses and steels. The consequence is a low layer and interface strength. A metallic copper manganese foam, which is oxidized under operation conditions into a conductive Cu1+xMn2–xO4 spinel, is presented in this work as a viable contact solution. The foam has been electrochemically tested in a single repeating unit setup for 350 hours of constant operation, followed by dynamic conditions with thermal cycles. After operation, a micro structural analysis using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction was carried out. It was confirmed that after oxidation/operation the manganese solely formed a CuMn-spinel phase, mixed with a CuO phase. A separate Mn-oxide phase was not found. The conductivity and contacting of the foam was sufficient for > 350 h of SOFC operation. With an initial serial resistance comparable to single cell tests using gold foil as contact material and moderate degradation rates, the CuMn foam presented itself as an interesting cathode contact solution.

Thin Films Made by Chemical Solution Deposition

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

Superconducting Thin Films Made by Chemical Solution Deposition

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.