The effect of strain on grains and grain boundaries in YBa2Cu3O7-δ coated 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.