The high upper critical field characteristic of the recently discovered iron-based superconducting chalcogenides opens the possibility of developing a new type of non-oxide high-field superconducting wires. In this work, we utilize a buffered metal template on which we grow a textured FeSe 0.5 Te 0.5 layer, an approach developed originally for high temperature superconducting coated conductors. These tapes carry high critical current densities (>1×10 4 A/cm 2 ) at about 4.2 K under magnetic field as high as 25 T, which are nearly isotropic to the field direction. This demonstrates a very promising future for iron chalcogenides for high field applications at liquid helium temperatures. Flux pinning force analysis indicates a point defect pinning mechanism, creating prospects for a straightforward approach to conductor optimization.

We report a sequence of continuous phase transformations in iron telluride, Fe1+yTe (y~0.1), which is observed by combining neutron diffraction, magnetic susceptibility, and specific heat measurements on single crystal samples. While a gradual increase of magnetic scattering near the wave vector (0.5, 0, 0.5) is seen below T = 70 K, a temperature where the discontinuous first order magneto-structural phase transition is found in systems with small y (< 0.06), the reduction of the lattice symmetry in Fe1.1Te only occurs at Ts = 63 K. Below TN = 57.5 K the long-range magnetic order develops, whose incommensurate wave vector Qm varies with temperature. Finally, at Tm ~ 45 K the system enters the low-T phase, where Qm is locked at (0.48, 0, 0.5). We conclude that these instabilities are weak compared to the strength of the underlying interactions, and we suggest that the impact of the Fe interstitials on the transitions can be treated with random-field models.Comment: revised resubmission, 8 pages, 5 figure

The nucleation and growth of the c-axis-aligned Yba2Cu3Ox on SrTiO3 and CeO2, from precursor films, were studied by examining quenched and fully processed specimens using transmission electron microscopy techniques. The precursor films, a stoichiometric mixture of fine-grained Y, Cu, and BaF2, were deposited using physical vapor deposition methods. An Y-Ba oxy-fluoride formed from the precursor contributed to the nucleation of Yba2Cu3Ox, while a liquid layer between the unreacted precursor and the Yba2Cu3Ox layer played an important role in the growth of Yba2Cu3Ox. However, the process of nucleation of Yba2Cu3Ox on SrTiO3 and CeO2 were significantly different.

The ex situ process has emerged as a popular technology for growing epitaxial YBa 2 Cu 3 O 7 (YBCO) for the second generation of coated conductors. The process combines low cost, ease of scale-up, the possibility of achieving high critical currents in relatively thick YBCO layers, as well as high tolerances to substrate misalignment. All of these factors explain why the process is increasingly becoming adapted by manufacturing companies for the production of YBCO wires. Studies of the barium fluoride variant of the ex situ process have offered rare insights into the structure, chemistry and pinning in ultra-thick, 5 µm, ex situ YBCO layers. The transition to thick YBCO layers is viewed as one of the key ingredients of the commercial success of the YBCO wire technology, which makes these studies especially relevant. This review is intended to be a comprehensive introduction into the history, physics and chemistry of barium fluoride processing, discussed concomitantly with recent results and trends in this field. Furthermore, comparisons are made between YBCO films made by ex situ and in situ deposition processes.

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