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7055465 
Journal Article 
Octahedral tilt transitions in the relaxor ferroelectric Na1/2Bi1/2TiO3 
Meyer, KaiC; Groeting, M; Albe, K; , 
2015 
Yes 
Journal of Solid State Chemistry
ISSN: 0022-4596
EISSN: 1095-726X 
ACADEMIC PRESS INC ELSEVIER SCIENCE 
SAN DIEGO 
117-122 
WOS:000355639500018 
The kinetics of octahedral tilt transitions in the lead-free relaxor material sodium bismuth titanate Na1/2Bi1/2TiO3 (NBT) is investigated by electronic structure calculations within density functional theory. Energy barriers for transitions between tetragonal, rhombohedral and orthorhombic tilts in cation configurations with [001]- and [111]-order on the A-sites are determined by nudged elastic band calculations. By tilting entire layers of octahedra simultaneously we find that the activation energy is lower for structures with 001-order compared to such with 111-order. The energetic coupling between differently tilted layers is, however, negligibly small. By introducing a single octahedral defect we create local tilt disorder and find that the deformation energy of the neighboring octahedra is less in a rhombohedral than in a tetragonal structure. By successively increasing the size of clusters of orthorhombic defects in a rhombohedral matrix with 001-order, we determine a critical cluster size of about 40 angstrom. Thus groups of about ten octahedra can be considered as nuclei for polar nanoregions, which are the cause of the experimentally observed relaxor behavior of NBT (C) 2015 Elsevier Inc. All rights reserved.