On the use of copper-based substrates for YBCO coated conductors

Abstract

It is well known that the recrystallization texture of heavily cold-rolled pure copperis almost completely cubic. However, one of the main drawbacks concerning the use of purecopper cube-textured substrates for YBCO coated conductor is the reduced secondaryrecrystallization temperature. The onset of secondary recrystallization (i.e., the occurrence ofabnormal grains with unpredictable orientation) in pure copper substrate was observed withinthe typical temperature range required for buffer layer and YBCO processing (600–850 °C). Toavoid the formation of abnormal grains the effect of both grain size adjustment (GSA) andrecrystallization annealing was analyzed. The combined use of a small initial grain size and arecrystallization two-step annealing (TSA) drastically reduced the presence of abnormal grainsin pure copper tapes.Another way to overcome the limitation imposed by the formation of abnormal grains is todeposit a buffer layer at temperatures where secondary recrystallization does not occur. Forexample, La2Zr2O7 (LZO) film with a high degree of epitaxy was grown by metal-organicdecomposition (MOD) at 1000 °C on pure copper substrate. In several samples the substrateunderwent secondary recrystallization. Our experiments indicate that the motion of grainboundaries occurring during secondary recrystallization process does not affect the quality ofLZO film.