Lattice reorientation in tetragonal PMN-PT thin film induced by focused ion beam preparation for transmission electron microscopy

摘要

Focused ion beam sample preparation for transmission electron microscopy (TEM) can induce relaxation mechanisms in epitaxial thin films. Here, we describe a relaxation mechanism that can occur in materials having a tetragonal structure. We investigated the lattice structure of a 600 nm thick 0.4[Pb(Mg_(1/3)Nb_(2/3))O_3] - 0.6[PbTiO_3] layer grown by epitaxy on (110) GdScO_3 substrate using geometrical phase analysis applied to high resolution TEM images. The lattice mismatch at the interface is expected to favor the formation of c-domains. However, it was measured that the out-of-plane lattice parameter can decrease abruptly along the growth direction and the transition depends on the thickness of the TEM lamella. Different observations indicate that the crystal flipped by 90° following the preparation of the sample, so that the c-axis is oriented in the thinning direction. Such a mechanism can easily lead to misinterpretations and might happen in other materials with a similar structure.