Doping of YBa2Cu3O7−δ (YBCO) has become an effective means of increasing the flux pinning and critical current densities (Jc) in thin film superconductors, while maintaining the transition temperature (Tc). In previous research efforts, our group showed that doping (Y1−xREx)BCO with typically deleterious rare earth (RE) elements can be used to improve the fil's current density via flux pinning when the x molar additions are less than 1%. However, data was only presented for different orders of magnitude (x = 0.1%, 1.0%, 10%) without consideration of optimization. The research presented here demonstrates that the deleterious RE elements can differ greatly in how broad the range of optimal doping concentration is, in addition to the relative doping concentration. Rare-earth elements Nd and Tb were compared due to the difference in degradation mechanisms: Nd additions results in Ba site substitution and Tb123 exhibits poor phase formation. Thin films of Nd and Tb doped YBCO films were grown by pulsed laser deposition (PLD) using standard deposition parameters for plain YBCO. The compositions studied were (Y1−xREx)BCO where x was varied from 0.0001 to 0.025 for Nd and 0.005 to 0.015 for Tb. Targets for PLD were prepared using solid state reaction and sintering procedures. All films were characterized for Jc and Tc by vibrating sample magnetometry. Data for Jc(H,T) and Tc were compared to undoped YBCO films processed under the same conditions. The results show a measurable increase in flux pinning for both different concentrations and range of Nd and Tb doping, with little decrease in Tc.

Various types of chemical doping have been reported as very effective methods to improve the superconducting properties of MgB2 superconductor. Specially, carbon doping via liquid type of carbon-containing compounds have been shown better superconducting properties. In this work, the liquid type of glycerin (C3H8O3) was used as a carbon dopant in MgB2 synthesis. The glycerin was mixed with a liquid media at a different ratio and then pretreated with refined boron powder. Then carbon doped MgB2 superconductor was synthesized through subsequent heat treatment of the pretreated boron powder with magnesium powder. Variation of the amount of carbon dopants and viscosity of the liquid media was correlated with critical current densities and other superconducting properties of MgB2 bulk. The effects of liquid carbon dopants on the superconducting properties also compared with those of solid dopants.

Recent efforts in investigating the mechanism of ion beam assisted deposition (IBAD) of biaxially textured thin films of magnesium oxide (MgO) template layers have shown that the texture develops suddenly during the initial 2 nm of deposition. To help understand and tune the behavior during this initial stage, we pre-deposited thin layers of MgO with no ion assist prior to IBAD growth of MgO. We found that biaxial texture develops for pre-deposited thicknesses < 2 nm, and that the thinnest layer tested, at 1 nm, resulted in the best qualitative RHEED image, indicative of good biaxial texture development. The texture developed during IBAD growth on the 1.5 nm pre-deposited layer is slightly worse and IBAD growth on the 2 nm pre-deposited layer produces a fiber texture. Application of these layers on an Al2O3 starting surface, which has been shown to impede texture development, improves the overall quality of the IBAD MgO and has some of the characteristics of a biaxially texture RHEED pattern. It is suggested that the use of thin (<2 nm) pre-deposited layers may eliminate the need for bed layers like Si3N4 and Y2O3 that are currently thought to be required for proper biaxial texture development in IBAD MgO.

In the recent development of the studies in iron-based superconductors, high-pressure experiments have been played an important role. Large enhancement of Tc with applying pressure and pressure-induced superconductivity were reported in LaFeAsO1-xFx. In this work, electrical, magnetic and structural measurements on 1111 type Ca(Fe1-xCox)AsF and 11 type Fe(Se1-xTex)0.92 under high pressure have been performed. For Ca(Fe1-xCox)AsF, the substitution of Co suppressed the magnetic and structural transitions and raised superconductivity. Pressure-induced superconductivity was observed for x = 0.0 and 0.05. The highest Tc was obtained in parent compound under high pressure, in contrast to LaFeAsO1-xFx. These results suggest that the substitution of Co increases carrier concentration and induces disorder in the FeAs superconducting layer. For FeTe0.92, pressure-induced superconductivity was not detected under high pressure up to 19 GPa, although the resistive anomaly due to the structural and magnetic phase transition was suppressed by applying pressure.

Measurements of the actual fluorine content x in the RO1−xFxFeAs-samples by wavelength-dispersive X-ray spectroscopy (WDX) reveal sample dependent discrepancies to the nominal fluorine content (initial weight). In particular for SmO1−xFxFeAs, the measured value only reached approximately half of the required value. In the lanthanum compound LaO1−xFxFeAs, we found a good agreement mainly for x>0.05, but the fluorine hardly goes into the sample for x<0.05. We used the measured fluorine content when plotting the electronic phase diagrams again and find a more consistent picture occurs as well for our samples as for comparison with the divers published data.

To apply the superconducting wire to power machines, it is necessary to conduct research on the characteristics of wire phase changes in connection with insulating layers. In this study, according to the presence or absence of insulating layers in the wire, and to the thickness of such layers, the wire's resistance increase trends and the characteristics of its recovery from quenching were examined by current-applied cycle at the temperatures of 90 K, 180 K and 250 K. Towards this end, YBCO thin-film wires that have the same critical temperatures and that have copper and stainless-steel stabilizing layers were prepared. One level and three and five levels of superior-performance polyimide pressure-sensitive adhesive tape was attached to the wires at a very low temperature. The eight prepared test samples were wound around the linear frames, then the wire's voltage and current created owing to the phase change characteristics were measured at each prescribed temperature, using the four-point probe method. Further, near the examination temperatures of 90 K, 180 K and 250 K the wire's resistance and recovery characteristics were examined by cycle.

In-field critical current Ic variations, detected using a short sample, angular Ic(77K, H=5.2kOe, Angle) measurement on the ends of a 20 m coated conductor tape fabricated by the MOD / RABiTS process, are shown to be variations in the Ic(H) anisotropy that exist on subcentimeter length scales. A Ic(75 K, H, Angle) study was performed on segments cut from the tape where the power law exponent of the field dependence, α, Ic ∼H−α was calculated for Ic(H, Angle) data. Two extrema behaviors, anisotropic and isotropic, were identified. The isotropic material is shown to outperform the anisotropic material for a wide range of fields and angles at T=26 K.