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Octahedral tilt transitions in the relaxor ferroelectric Na1/2Bi1/2TiO3

Meyer, Kai-Christian and Gröting, Melanie and Albe, Karsten (2015):
Octahedral tilt transitions in the relaxor ferroelectric Na1/2Bi1/2TiO3.
In: Journal of Solid State Chemistry, pp. 117-122, 227, ISSN 00224596, [Online-Edition: http://dx.doi.org/10.1016/j.jssc.2015.03.023],
[Article]

Abstract

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 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.

Item Type: Article
Erschienen: 2015
Creators: Meyer, Kai-Christian and Gröting, Melanie and Albe, Karsten
Title: Octahedral tilt transitions in the relaxor ferroelectric Na1/2Bi1/2TiO3
Language: English
Abstract:

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 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.

Journal or Publication Title: Journal of Solid State Chemistry
Volume: 227
Uncontrolled Keywords: Sodium bismuth titanate, Planar defects, Tilt kinetics, Short-range order, Density functional theory, Polar nanoregions
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ) > Hochleistungsrechner
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ)
Zentrale Einrichtungen
Date Deposited: 16 Apr 2015 08:17
Official URL: http://dx.doi.org/10.1016/j.jssc.2015.03.023
Identification Number: doi:10.1016/j.jssc.2015.03.023
Funders: This work has been financially supported by the DFG Priority Programme 1599 “Caloric Effects in Ferroic Materials: New Concepts for Cooling” (Grant no. AL 578/16-1)., The authors gratefully acknowledge the computing time granted by the John von Neumann Institute for Computing (NIC) and provided on the supercomputer JUROPA at Jülich Supercomputing Centre (JSC)., Moreover, computing time was granted on the Lichtenberg-High Performance Computer at TU Darmstadt.
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