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Calorimetric and magnetic AC loss measurements are made on a pair of technology quadrupole (TQ) class cables, one with and the other without a stainless steel core. The coupling losses are compared to the cables' hysteretic losses determined at the same time, the latter being compared to the magnetically measured hysteretic losses of individual strand segments.

A standard Bloch-Gruneisen (B-G)-based connectivity model was applied to experimental data on binary and heavily doped Mg[B.sub.2] samples as well as published resistivity data to determine the highest attainable [J.sub.c] in a given class of samples. The results from calorimetric measurements that probed the homogeneity of the doped samples in terms of the roundness of the electronic specific heat jump near [T.sub.c] are also discussed.

Advances in crystal growth have allowed for synthesis of large single crystals of Nd 1 + ∊ Fe 4 B 4 , a well-known phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd 1 + ∊ Fe 4 B 4 sample with a distribution of ∊ that skews towards the solubility limit of Nd near ∊ ≈ 1 7 . Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previously reported values in the Nd 1 + ∊ Fe 4 B 4 system. We also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have created a high pressure, high temperature material synthesis apparatus. [•] This apparatus is programmable and capable of various thermal analysis procedures. [•] Using our apparatus we have established the peritectic transition temperature of MgB2. [•] This temperature is 300°C lower than established values for the same pressure. [•] We have shown that this discrepancy is likely the result of impurities such as C. [ABSTRACT FROM AUTHOR]

Highlights: [•] We notice that when MgB2 is doped so as to increase its Birr and Bc2 , the low-field Jc is decreased. [•] We propose that this phenomenon is intrinsic to superconductors with a large variability in Bc2 . [•] Using the surface pinning function, we have shown that increases in Bc2 will decrease low-B Jc . [•] For an application where low-B Jc needs to be maximized, doping will be deleterious. [•] Rather, increases in connectivity should be explored. [Copyright &y& Elsevier]

Abstract: The decomposition of malic acid (C4H6O5) in the presence of Mg and B was studied using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) which revealed that malic acid reacted with Mg but not B. Also, the addition of toluene (C7H8) to dissolve malic acid followed by subsequent drying resulted in no reaction with Mg, indicating that the malic acid had decomposed during the dissolution/drying stage. The total carbon contributed by toluene versus a toluene/5wt.% malic acid mixture was measured using a LECO CS600 carbon analyzer. The toluene sample contained ∼0.4wt.% C while the toluene/malic acid mixture had ∼1.5wt.% C, demonstrating that the toluene contributed a significant amount of carbon to the final product. Resistivity measurements on powder-in-tube MgB2 monofilamentary wires established that the toluene/malic acid doped sample had the highest Bc 2. However, the toluene-only sample had the highest transport Jc over most of the magnetic field range (0–9T), equaled only by that of toluene/malic-acid sample in fields above 9T. [Copyright &y& Elsevier]

Abstract: Improvements in B c2, B irr, and high field transport J cs are crucial for many MgB2 applications. As transport J c is inextricably linked with microstructure, a knowledge of the detailed influence of two of the most practical variables – Mg/B ratios and SiC additions – on microstructure, B c2/B irr, and high field J c, is of interest. In this work, the influence of Mg/B ratios on microstructure, B irr, and transport J c was investigated in MgB2 strands with and without SiC doping. The binary compositions chosen were Mg x B2 where x =0.85, 0.90, 1.0, 1.10, and 1.15 in monofilamentary strands. In general, high Mg molar percentages were seen to increase transport J c, especially at higher fields. At 8 T, for example, heat treatments at 700°C for 40min yielded J cs at 4.2K which ranged from 5.8×103 A/cm2 for x =0.85 to 2.73×104 A/cm2 at x =1.15. Microstructures evolved from powdery (B-rich) to web-like (Mg-rich). In a second set of samples, Mg-rich stoichiometries were investigated with and without SiC. High field transport J cs increased, and the microstructure appeared to densify. Both excess Mg and SiC doping significantly increased high field J c. The highest transport result was seen for SiC dopant (5mol%) added to 15% excess Mg strands, which yielded a transport J c at 4.2K and 8T of 5×104 A/cm2. Variable temperature analysis was performed on the 15% excess Mg strands with and without SiC in fields of 0–15T. At temperatures below 20K, excess Mg+SiC doping performed best, while above 20K, excess Mg without SiC had better transport properties. [Copyright &y& Elsevier]

Abstract: Cu sheathed polycrystalline Ba0.6K0.4Fe2As2 superconducting wire was prepared by a two-step powder-in-tube method. A pressure of 2GPa was applied to a short sample before heat treatment. Magnetization and transport measurements were performed to investigate the effects of cold high pressure densification on the microstructure and superconductivity. The cold pressed sample shows an improved self-field transport critical current density of 2.8×104 A/cm2 (I c =83A) at 4.2K, which is nearly as twice as the unpressed sample. However, both samples manifest pronounced weak-link behavior, suggesting the technique need to be further optimized. The comparison of properties between pressed and unpressed sample and related mechanism was discussed. [Copyright &y& Elsevier]