Phase Equilibria Relationships of High-Tc Superconductors

Abstract

Accomplishments SummaryAs an integral part of a DOE R&D program (1987DOE R&D program ( -2007 3227-3229 (2005). During the course of this work, we developed extensive collaborations with several DOE laboratories. Our studies involved bulk materials, single crystals (e.g. Phys. Rev. B 41, 4220, 1990) and thin films (e.g. Appl. Phys. Lett, 88 102507, 2006; Appl. Phys. Lett. 90,102508, 2007). In addition, we also studied the interactions (phase equilibria and kinetics) of superconductor phases with buffer layers and substrates of the coated conductors (e.g. J. Solid State Chem., 470(5-6) [345][346][347][348][349][350][351] 2010).Various experimental challenges were successfully dealt with, including atmospheric contamination, substrate reaction, gas-phase interactions, and the complexity of multiphase products. Results were used to guide materials processing for optimal onset T c , critical current density, high-field behavior, mechanical properties, and cost/performance ratio, including the development of novel flux-pinning techniques.In addition, we have studied the theory and phenomena of phase transformation of the high T c BaR 2 Cu 3 O 6+x phases; the explanation of the trend of melting temperature of BaR 2 Cu 3 O 6+x as a function of the size of the ionic radius of R; phase formation studies of the (Pb,Bi):Sr:Ca:Cu (2212 and 2223) oxide phases.This work resulted in a number of awards and more than 150 publications. In the course of the project we were awarded the highest rating three times during the required annual DOE peer reviews. We were also given the Department of Commerce bronze awards in 2002 and in 2008.The list of publications as a result of the partial support of the DOE program is summarized in the following pages. Fifteen selected papers are attached. 46. W. Wong-Ng, E.J. Gonzalez, G.J, Piermarini, C. Wolters, and J. Schwartz, X-ray diffraction study of high T c materials under high pressures, Adv. X-Ray Anal. (CD-ROM format), 40 (1996 Since the discovery of high-T c superconducting oxides in 1986, 1 extensive research has led to a variety of prototype applications. In particular, the low-cost second generation high-T c wire and tape ͑coated conductor͒ technology 2-5 is promising for large-scale commercialization of superconductors. The coated-conductor materials are based on Ba 2 YCu 3 O 6+x ͑Y-213͒ and its lanthanide variants, Ba 2 RCu 3 O 6+x ͑R-213, R = lanthanides͒. 6,7 Major techniques for processing biaxially textured templates include the rolling-assisted biaxially textured substrate ͑so-called RABiTS͒ 2,3 and ion-beam-assisted deposition 4,5 methods. The BaF 2 ex situ process is among the leading candidates for producing long-length tapes with high performance. [8][9][10][11] Information on phase relationships in the Ba-Y-Cu-O system is critical for manufacturing of coated conductors, particularly for flux pinning applications. List of publications:Previously, we used in situ high-temperature x-ray diffraction ͑HTXRD͒ 11,12 to establish phase relations in high-T c superconductor Ba-Y...