Microstructural characterization of thick YBa₂Cu₃O_7−δ films on improved rolling-assisted biaxially textured substrates

Abstract

The microstructural changes associated with the reduced dependence of critical current density (J c ) versus thickness of thick, epitaxial YBa 2 Cu 3 O 7−␦ (YBCO) films on rolling-assisted biaxially textured substrates (RABiTS) were investigated. Pulsed laser deposited YBCO films varying in thickness from 1.0 to 6.4 m on RABiTS with an architecture of Ni-3 at.% W/Y 2 O 3 /yttrium-stabilized-zirconia/CeO 2 /YBCO were prepared for cross-sectional transmission electron microscopy studies. Dramatic improvements in physical properties and microstructural quality were observed resulting from the use of Ni-3 at.% W substrates, which provided a sharper texture over earlier Ni substrates, and replacement of CeO 2 with Y 2 O 3 as the seed layer within the buffers. The YBCO films showed exceptional orientation up to 6.4 m thickness, with no misoriented grains or dead layers observed and only limited reaction between the YBCO and CeO 2 cap layer. The high quality of the films was also attributed in part to the formation of a tungsten oxide layer forming at the top of the Ni-3% W substrate, limiting the growth of deleterious NiO into the conductor.

High Critical Current YBa2Cu3O7−δ Thick Films on Improved Rolling‐Assisted Biaxially Textured Substrates (RABiTS™)

“…This is in stark contrast to the TEM of the 3.0 m film on RABiTS with configuration CeO 2 /YSZ/CeO 2 /Ni shown in Fig. 4 where the CeO 2 cap layer was completely reacted with the YBCO layer 10,12,13 . This improved microstructure, assumed to be because of more suitable characteristics of the buffer layer stack with thick Y 2 O 3 seed layer, is certainly a contributing factor for the improved thickness dependence of J c observed in this study.…”

“… Cross‐sectional bright field transmission electron microscopy images of a 3.0 and 2.9 μm YBa 2 Cu 3 O 7−δ (YBCO) films on (a) CeO 2 /YSZ/CeO 2 /Ni (after Leonard et al 12,13 …”

“…Microstructural study for thick films was performed carefully by TEM to examine structural defects and disorders in the grown films and a report detailing the microstructural characteristics with increasing YBCO thickness was reported elsewhere 12,13 . Cross‐sectional TEM was also performed for the 6.4 μm‐thick YBCO film 12 . Surprisingly, a change to the predominant porous structures observed elsewhere was not observed in the 6.4 μm‐thick YBCO film on RABiTS.…”

Through-thickness superconducting and normal-state transport properties revealed by thinning of thick film ex situ YBa2Cu3O7−x coated conductors

“…Subsequent work by Foltyn and others has shown that these ''dead'' layers are not endemic of thick YBCO coated conductors, but instead dependent on the growth conditions. [8][9][10][11] In this letter, we report ion-milling studies on YBCO grown by the BaF 2 ex situ process on IBAD-YSZ buffered metal substrates. The details of the BaF 2 ex situ growth process 7,12 and preparation of IBAD-YSZ buffered metal tapes 13 are given elsewhere.…”

Iridium: An Oxygen Diffusion Barrier and a Conductive Seed Layer for RABiTS-Based Coated Conductors

“…Generally, at these extreme growth conditions, an unfavorable orientational relationship results between the native oxide and metal substrate, degrading the subsequent nucleation of crystalline oxide buffer layers. Although epitaxial growth of various oxide layers have been successfully achieved over the years by effectively controlling the surface conditions of metallic tapes [1], insulating interfacial metal-oxide formation during the subsequent deposition of (YBCO) films has not been completely prevented [2], [3]. Regarding a fully conductive architecture, this problem is a major concern since it causes a partial or total loss of electrical connection between the HTS layer and the underlying substrate material [4], [5].…”