Strain release and twin structure in GdBa2Cu3O7-δ films on (001) SrTiO3 and NdGaO3 -: art. no. 113402

Ultrathin films of GdBa2Cu3O7-delta grown by pulsed laser deposition on NdGaO3 (001) and SrTiO3 (001) were studied by grazing incidence x-ray diffraction. The critical thicknesses t(c) was found to be 50 nm on SrTiO3 (001). On NdGaO3 (001), the shear distortion introduced by the substrate is released in two stages at 15 nm and 40 nm thickness by the formation of disclinations with orthogonal pseudo-Burgers vectors. The twin structure forms in the films at the first stage of strain relief, and as a consequence the twin boundaries are aligned unidirectionally. Calculated values for the critical thickness are too small for GdBCO/STO suggesting the existence of other mechanisms of strain relief, which is corroborated by our experimental findings.