The effect of strain on grains and grain boundaries in YBa2Cu3O7−δcoated conductors

The role of grains and grain boundaries in producing reversible strain effects on the transport current critical current density (Jc) of YBa2Cu3O7−δ (YBCO) coated conductors that are produced with metal–organic deposition (MOD) was investigated. The strain (ε) dependence of Jc for full-width coated conductors is compared with that for samples in which the current transport was limited to a few or single grain boundaries by cutting narrow tracks with a laser or focused ion beam, as well as with thin films deposited on bicrystalline SrTiO3 substrates by use of pulsed-laser deposition (PLD). Our results show that the dependences of Jc on ε for the grains and for the grain boundaries from the two kinds of YBCO samples can be expressed by the same function, however with a greater effective tensile strain at the grain boundaries than in the grains. The really striking result is that the grain boundary strain is 5–10 times higher for grain boundaries of in situ PLD grown bicrystals as compared to the aperiodic, meandered, nonplanar grain boundaries that develop in ex situ grown MOD-YBCO in the coated conductor of this study.