Improved current transport properties of post annealed Y1Ba2Cu3O7−x thin films using Ag doping

Abstract

The influence of Ag doping on the transport properties of Y 1 Ba 2 Cu 3 O 7Ϫx thin films prepared by Y, BaF 2 , and Cu co-evaporation and optimized ex situ post annealing has been investigated. Both undoped and Ag doped films have values of T c above 90 K, but J c ͑77 K͒ is highly dependent on the nominal thickness ͑t nom ͒ of the as-deposited film. For undoped films with t nom р300 nm J c ͑77 K͒ ͑ӷ10 6 A/cm 2 ͒ decreases monotonically with increasing film thickness. Above 300 nm J c ͑77 K͒ decreases rapidly to values below 5ϫ10 5 A/cm 2 . Ag doped films with t nom у200 nm have higher J c ͑77 K͒ values than those of undoped films. Ag doped films have a maximum in J c ͑77 K͒ around 250 nm. As for the undoped films, there is a large decrease in J c ͑77 K͒ for Ag doped films with t nom у300 nm. It was found that the higher values of J c ͑77 K͒ for the Ag doped films were due to a better epitaxial growth of the YBCO compound. The low values of J c ͑77 K͒ for both undoped and Ag doped single layer films with t nom у300 nm were found to be due to the absence of 1-2-4 inclusions in these films. Based on these findings high J c ͑77 K͒ films with t nom Ͼ300 nm were grown by successive deposition and annealing of films with t nom Ͻ300 nm on top of each other. A 2ϫ150 nm undoped film was found to have a J c ͑77 K͒ value of 4, 1ϫ10 6 A/cm 2 . This is almost a doubling of the J c ͑77 K͒ value as compared to the value for the 300 nm single layer undoped film ͑2,2ϫ10 6 A/cm 2 ͒. Ag doped double layer films of 2ϫ150 nm and 2ϫ215 nm had comparable J c ͑77 K͒ values ͑5,8ϫ10 6 and 5,6ϫ10 6 A/cm 2 , respectively͒. In comparison with the undoped 2ϫ150 nm film J c ͑77 K͒ is thus further increased ͑by about 50%͒ when doping with Ag.

Increased flux pinning in YBa 2 Cu 3 O 7−δ thin-film devices through embedding of Au nano crystals

“…For this reason numerous investigations were carried out regarding possibilities to pin flux vortices without changing the sensor inductance. It was reported that well-placed microstructural voids in the superconductor [3], the preparation of normal conducting channels by ion irradiation of the thin film [4], local defects and outgrowths [5] or local inserts of normal conducting materials like silver or gold [6][7][8] could lead to an enhanced flux pinning. One possibility to draw conclusion on an additional pinning of flux vortices is to measure the critical current density j c of the modified superconductor.…”

Liquid source metal–organic chemical-vapor deposition of high-quality YBa2Cu3O7−x films on polycrystalline silver substrates

“…In fact, there are many reports of silver in dopant quantities also improving the superconducting properties of YBCO. [4][5][6][7] This letter reports the growth by liquid delivery ͑LD͒ metal-organic chemical-vapor deposition ͑MOCVD͒ of high-quality YBCO thin films on polycrystalline silver substrates. YBa 2 Cu 3 O 7Ϫx films were grown by liquid delivery MOCVD using the inverted vertical reactor configuration described previously.…”

Laser-Assisted Field Evaporation of (R = Gd, Sm) High-Temperature Superconducting Coated Conductors

“…During the deposition cycles, a controlled excess of Gd material is introduced to promote Gd-rich secondary phase precipitation during the oxidation cycles. Elemental Ag was co-evaporated alongside Gd, Ba, and Cu during HTS deposition, which is known to promote YBa 2 Cu 3 O 7−d oriented growth (Matsumoto et al, 1989;Chuang et al, 1995;Clausen et al, 1996), improve mechanical properties by filling voids (although no voids were found in this study) (Singh et al, 1993;Chuang et al, 1995), increase critical current densities (Matsumoto et al, 1989;Chuang et al, 1995;Misra et al, 1995;Clausen et al, 1996), and improve thermal cycling (Singh et al, 1993). The Sm sample was not, however, doped with Ag.…”

“…Non-superconducting secondary phases (as well as the broader spectrum of microstructural defects) provide a flux pinning mechanism whereby the magnetic flux quanta are pinned in-place, inhibiting flux movement (Jung et al, 1990;Murakami et al, 1991Murakami et al, , 1994. As a result, a significant amount of effort has been spent testing different pinning methodologies to mitigate flux creep: such as crystallographic defects (Sauerzopf, 1998;Wang et al, 2008), secondary phases (Murakami et al, 1991;Lee et al, 1992;Cantoni & Nissen, 1993;Jiao et al, 2010), or doping (Clausen et al, 1996;Goyal et al, 2005;Ichinose et al, 2008;Mele et al, 2009;Ko et al, 2011;Horide et al, 2013;Matsumoto et al, 2014;Miura et al, 2015). Weak links arise from depletion of the hole concentration at larger misorientation grain boundaries, resulting from oxygen variation or arrangement (Vargas et al, 1997;Babcock, 1999).…”