- Yu-Tsun Shao, The University of Illinois, Urbana-Champaign
Emergent properties arise from correlated lattice and charge interactions in complex, multi-element crystals. For relaxor-ferroelectric crystals, the lattice, polarization, and charge interactions must be understood to optimize and design new functional materials based on the emergent properties. The speaker will discuss the development of techniques based on scanning convergent beam electron diffraction (SCBED) to detect local structural variations such as crystal symmetry, strain, and polarization. CBED patterns were recorded as a convergent, nanometer-sized electron probe was rastered over a region of a crystal. SCBED was applied to BaTiO3 and (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (x = 0.08) single crystals. In BaTiO3, the polarization and crystal symmetry are expected to be uniform within a ferroelectric domain. However, results from SCBED demonstrated that crystal symmetry is not homogeneous; regions of ~15 nm retaining almost perfect symmetry are interspersed in regions of lower symmetry. In PZN-8%PT, the SCBED results show that local lattice-rotation vortex occurred at the 50° monoclinic charged domain boundary. The speaker will also describe how SCBED may be complementary to experimental techniques such as STEM-EELS and atom probe tomography for solving challenging problems in materials science.