@article{ishmael_luo_white_hunte_liu_mandzy_muth_naderi_ye_hunt_et al._2013, title={Enhanced Quench Propagation in Bi2Sr2CaCu2Ox and YBa2Cu3O7-x Coils via a Nanoscale Doped-Titania-Based Thermally Conducting Electrical Insulator}, volume={23}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2013.2269535}, abstractNote={The significant amount of energy stored in a large high-field superconducting magnet can be sufficient to destroy the coil in the event of an unprotected quench. For magnets based on high-temperature superconductors (HTSs), such as Bi2Sr2CaCu2Ox (Bi2212) and YBa2Cu3O7-x (YBCO), quench protection is particularly challenging due to slow normal zone propagation. A previous computational study showed that the quench behavior of HTS magnets is significantly improved if the turn-to-turn electrical insulation is thermally conducting, enhancing 3-D normal zone propagation. Here, a new doped-titania electrical insulation with high thermal conductivity is evaluated. The thermal conductivity of the insulation is measured at cryogenic temperatures, and its chemical compatibility with Bi2212 round wires is determined. Thin layers of the insulation are deposited onto the surface of Bi2212 and YBCO wires, which are then wound into small coils to study the quench behavior. Results show that the critical current and homogeneity of Bi2212 coils are improved relative to coils reacted with mullite insulation. Relative to similar coils with conventional insulation (mullite for Bi2212 and Kapton for YBCO), the turn-to-turn quench propagation is increased by a factor of 2.8 in Bi2212 coils at 4.2 K and self-field and by a factor of 2.5 in YBCO coils at 4.2 K and 5 T. These results indicate that doped-titania insulation may significantly improve Bi2212 and YBCO coils. Increased normal zone propagation velocity enhances quench detection and quench protection, and the thinness of the insulation relative to the most common alternatives increases the magnet winding pack current density and reduces the coil specific heat.}, number={5}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Ishmael, Sasha and Luo, Haojun and White, Marvis and Hunte, Frank and Liu, X. T. and Mandzy, Natalia and Muth, John F. and Naderi, Golsa and Ye, Liyang and Hunt, Andrew T. and et al.}, year={2013}, month={Oct} }
 @article{naderi_liu_nachtrab_schwartz_2013, title={Understanding processing-microstructure-properties relationships in Bi2Sr2CaCu2Ox/Ag round wires and enhanced transport through saw-tooth processing}, volume={26}, ISSN={["1361-6668"]}, DOI={10.1088/0953-2048/26/10/105010}, abstractNote={Superconducting magnets generating magnetic fields above 25 T are needed for many scientific applications. Due to fundamental limitations in NbTi and Nb3Sn, such high-field superconducting magnets require alternative high-field conductors. One candidate conductor is round wire composites of Bi2Sr2CaCu2Ox sheathed in a Ag-alloy matrix (Bi2212/Ag). The performance of such wires is sensitive to the heat treatment, so improvements in the critical current density (Jc) require a thorough understanding of the processing–structure–properties relationships. Here we present a two-part study. In part I, a new heat treatment approach, saw-tooth processing (STP), is introduced based upon previous results showing that Bi2212 nucleation is site-saturation limited. The microstructural evolution of Bi2212 filaments during processing is discussed and results from STP are compared with those from other processes. STP is shown to increase Jc by 120% and 70% relative to partial-melt processing at 5 T and self-field respectively, and by 65% and 34% relative to split-melt processing. Yet STP also complicates the heat treatment by introducing a number of new heat treatment variables that affect the grain morphology, phase assemblage and oxygen content of the Bi2212 filaments and thus the transport properties. In part II, the effects of STP heat treatment parameters on the microstructure and transport properties are discussed. It is shown that wires with the highest transport critical current densities primarily have filaments with two types of microstructures, one comprised primarily of highly textured Bi2212 grains, and another with a noticeable amount of Bi2Sr2CuOx with the Bi2212.}, number={10}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Naderi, Golsa and Liu, Xiaotao and Nachtrab, William and Schwartz, Justin}, year={2013}, month={Oct} }
 @article{kajbafvala_nachtrab_lu_hunte_liu_cheggour_wong_schwartz_2012, title={Dispersion-Strengthened Silver Alumina for Sheathing Bi2Sr2CaCu2O8+x Multifilamentary Wire}, volume={22}, ISSN={["1558-2515"]}, DOI={10.1109/tasc.2011.2179296}, abstractNote={High-strength high-elastic-modulus dispersion-strengthened (DS) silver aluminum alloys are studied for sheathing Bi2Sr2CaCu2O8 + x (Bi2212) round wire. DS is an effective method for producing a fine grain metallurgical structure that is resistant to softening during high-temperature heat treatment. Here, DS Ag/0.5-wt.% Al (AgAl) alloy sheet is produced using powder metallurgy and is compared with Ag/0.2-wt.% Mg (AgMg) alloy, which is currently the most common alloy used for Bi2212 wire. Room temperature (RT), 77- and 4.0-K tensile tests, Vickers microhardness, optical microscopy, field emission scanning electron microscopy, and electrical resistivity measurements are compared. Furthermore, Bi2212/AgMg and Bi2212/AgAl wires are produced and compared for short-sample and coil Ic (4.2 K; self-field). It is found that the AgAl solid wire shows high yield stress and ultimate tensile strength in the annealed condition at both RT and 4.0 K, as well as significant ductility at 4.0 K. Electrical transport measurements show that the Bi2212/AgAl wires perform as well or better than Bi2212/AgMg wires. Furthermore, no leakage is observed after partial melt processing (PMP) of Bi2212/AgAl spirals. After PMP, the Bi2212/AgAl wire not only has yield and tensile stresses slightly higher than those of the Bi2212/AgMg wire but also exhibits >; 2% elongation, which is several times higher than that of Bi2212/AgMg.}, number={1}, journal={IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY}, author={Kajbafvala, Amir and Nachtrab, William and Lu, Xi Feng and Hunte, Frank and Liu, Xiaotao and Cheggour, Najib and Wong, Terence and Schwartz, Justin}, year={2012}, month={Feb} }
 @article{carson_ward_liu_schwartz_gerhardt_tannenbaum_2012, title={Dopant-Controlled Crystallization in Metal-Organic Frameworks: The Role of Copper(II) in Zinc 1,4-Benzenedicarboxylate}, volume={116}, ISSN={["1932-7455"]}, DOI={10.1021/jp2117032}, abstractNote={A series of Zn–Cu 1,4-benzenedicarboxylate(bdc) metal organic frameworks(MOF) have been synthesized by introducing N,N-dimethylformamide(DMF) solutions of 1,4-benzenedicarboxylic acid to metal salt solutions with a range of concentrations of Cu(NO3)2 and Zn(NO3)2 across the entire composition range. At the Zn-rich side of the range, the presence of Cu(II) had the effect of changing the polymorph of the solid from the predominantly P21/n structure, associated with MOF-2, to the C2/m structure, shared with Cu(bdc). There was an associated change in crystal morphology that accompanied the addition of a Cu salt impurity. BET surface area measurements of the thermally desolvated product showed that the surface area of the Zn(bdc) increased with the addition of Cu. At the Cu-rich side, magnetic susceptibility measurements indicated that the presence of the Zn impurity increased the fraction of paramagnetic Cu centers, suggesting the formation of a large fraction of heterometallic secondary building units(hSBU) ...}, number={29}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Carson, Cantwell G. and Ward, Jason and Liu, Xiao Tao and Schwartz, Justin and Gerhardt, Rosario A. and Tannenbaum, Rina}, year={2012}, month={Jul}, pages={15322–15328} }
 @article{gupta_zaidi_melton_malguth_yu_liu_liu_schwartz_ferguson_2011, title={Electrical and magnetic properties of Ga1-xGdxN grown by metal organic chemical vapor deposition}, volume={110}, ISSN={["1089-7550"]}, DOI={10.1063/1.3656019}, abstractNote={This paper presents the first report on Gd doping (0%–4%) of GaN thin films by metal organic chemical vapor deposition. The Ga1−xGdxN films grown in this study were found to be of good crystalline quality, single-phase, and unstrained, with a high saturation magnetization strength of 20 emu/cm3 being obtained for GaN films doped with 2% Gd at room temperature. Furthermore, these films were found to be conductive with an enhanced n-type behavior suggesting that unintentional donors are responsible for stabilizing the ferromagnetic phase in as-grown Ga1−xGdxN. Additionally, it was found that this magnetization can be enhanced by n-(Si: 1018 cm−3) and p-(Mg: 1019 cm−3) doping to 110 emu/cm3 and ∼500 emu/cm3, respectively. This paper shows empirically that holes are more efficient in stabilizing the ferromagnetic phase as compared to electrons. Overall, this research has resulted in a room temperature ferromagnetic dilute magnetic semiconductor that is conductive and whose magnetic properties can be tuned by carrier doping thus providing a path towards realizing spintronic devices.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Gupta, Shalini and Zaidi, Tahir and Melton, Andrew and Malguth, Enno and Yu, Hongbo and Liu, Zhiqiang and Liu, Xiaotao and Schwartz, Justin and Ferguson, Ian T.}, year={2011}, month={Oct} }