The effect of strain on grains and grain boundaries inYBa2Cu3O7−δ coated conductors**Work partially supported by NIST, a US government agency, not subject to US copyright.Certain commercial materials are referred to in this paper to foster understanding.Such identification does not imply recommendation or endorsement by NIST, nordoes it imply that the materials identified are necessary the best available for thepurpose.

Abstract

The role of grains and grain boundaries in producing reversiblestrain effects on the transport current critical current density (Jc) ofYBa2Cu3O7−δ (YBCO)coated conductors that are produced with metal–organic deposition (MOD) was investigated. The strain (ε) dependenceof Jc for full-width coated conductors is compared with that for samples in which the currenttransport was limited to a few or single grain boundaries by cutting narrow tracks with alaser or focused ion beam, as well as with thin films deposited on bicrystallineSrTiO3 substrates by use of pulsed-laser deposition (PLD). Our results show that the dependences ofJc onε for the grains and for the grain boundaries from the two kinds of YBCO samples can beexpressed by the same function, however with a greater effective tensile strain at thegrain boundaries than in the grains. The really striking result is that the grainboundary strain is 5–10 times higher for grain boundaries of in situ PLD grownbicrystals as compared to the aperiodic, meandered, nonplanar grain boundaries thatdevelop in ex situ grown MOD-YBCO in the coated conductor of this study.