Octahedral tilt transitions in the relaxor ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3}

Journal Article · Wed Jul 15 00:00:00 EDT 2015 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2015.03.023· OSTI ID:22475689

Meyer, Kai-Christian; Gröting, Melanie; Albe, Karsten

The kinetics of octahedral tilt transitions in the lead-free relaxor material sodium bismuth titanate Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} (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 Å . 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. - Graphical abstract: Nine orthorhombic oxygen octahedral tilt defects in a rhombohedral tilt configuration. - Highlights: • Chemical order influences energy barriers of octahedral tilt transitions. • The octahedral deformation energy is lower in rhombohedral phases. • Tilt defect clusters are more likely in rhombohedral structures. • Tilt defect clusters can act as nuclei for polar nanoregions.

• OSTI ID: 22475689
• Journal Information: Journal of Solid State Chemistry, Vol. 227; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
BISMUTH COMPOUNDS
CATIONS
COMPARATIVE EVALUATIONS
COUPLING
CRYSTAL DEFECTS
DEFORMATION
DENSITY FUNCTIONAL METHOD
DIFFUSION BARRIERS
ELECTRONIC STRUCTURE
FERROELECTRIC MATERIALS
LAYERS
MATRIX MATERIALS
ORTHORHOMBIC LATTICES
SODIUM COMPOUNDS
TITANATES
TRIGONAL LATTICES