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Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na_1/2Bi_1/2TiO_3−0.036BaTi_O3

Pforr, Florian and Meyer, Kai-Christian and Major, Marton and Albe, Karsten and Donner, Wolfgang and Stuhr, Uwe and Ivanov, Alexandre (2017):
Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na_1/2Bi_1/2TiO_3−0.036BaTi_O3.
In: Physical Review B, 96, (18), ISSN 2469-9950,
DOI: 10.1103/PhysRevB.96.184107,
[Online-Edition: https://doi.org/10.1103/PhysRevB.96.184107],
[Article]

Abstract

The local dynamics of the lead-free relaxor 0.964Na_1/2Bi_12TiO_3−0.036BaTiO_3(NBT-3.6BT) have been investigated by a combination of quasielastic neutron-scattering (QENS) and ab initio molecular dynamics simulations. In a previous paper, we were able to show that the tetragonal platelets in the microstructure are crucial for understanding the dielectric properties of NBT-3.6BT [Pforr et al., Phys. Rev. B 94, 014105 (2016)]. To investigate their dynamics, ab initio molecular dynamics simulations were carried out using Na_1/2Bi_1/2TiO_3 with 001 cation order as a simple model system for the tetragonal platelets in NBT-3.6BT. Similarly, 111-ordered Na_1/2Bi_1/2TiO_3 was used as a model for the rhombohedral matrix. The measured single-crystal QENS spectra could be reproduced by a linear combination of calculated spectra. We find that the relaxational dynamics of NBT-3.6BT are concentrated in the tetragonal platelets. Chaotic stages, during which the local tilt order changes incessantly on the time scale of several picoseconds, cause the most significant contribution to the quasielastic intensity. They can be regarded as an excited state of tetragonal platelets, whose relaxation back into a quasistable state might explain the frequency dependence of the dielectric properties of NBT-3.6BT in the 100 GHz to THz range. This substantiates the assumption that the relaxor properties of NBT-3.6BT originate from the tetragonal platelets.

Item Type: Article
Erschienen: 2017
Creators: Pforr, Florian and Meyer, Kai-Christian and Major, Marton and Albe, Karsten and Donner, Wolfgang and Stuhr, Uwe and Ivanov, Alexandre
Title: Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na_1/2Bi_1/2TiO_3−0.036BaTi_O3
Language: English
Abstract:

The local dynamics of the lead-free relaxor 0.964Na_1/2Bi_12TiO_3−0.036BaTiO_3(NBT-3.6BT) have been investigated by a combination of quasielastic neutron-scattering (QENS) and ab initio molecular dynamics simulations. In a previous paper, we were able to show that the tetragonal platelets in the microstructure are crucial for understanding the dielectric properties of NBT-3.6BT [Pforr et al., Phys. Rev. B 94, 014105 (2016)]. To investigate their dynamics, ab initio molecular dynamics simulations were carried out using Na_1/2Bi_1/2TiO_3 with 001 cation order as a simple model system for the tetragonal platelets in NBT-3.6BT. Similarly, 111-ordered Na_1/2Bi_1/2TiO_3 was used as a model for the rhombohedral matrix. The measured single-crystal QENS spectra could be reproduced by a linear combination of calculated spectra. We find that the relaxational dynamics of NBT-3.6BT are concentrated in the tetragonal platelets. Chaotic stages, during which the local tilt order changes incessantly on the time scale of several picoseconds, cause the most significant contribution to the quasielastic intensity. They can be regarded as an excited state of tetragonal platelets, whose relaxation back into a quasistable state might explain the frequency dependence of the dielectric properties of NBT-3.6BT in the 100 GHz to THz range. This substantiates the assumption that the relaxor properties of NBT-3.6BT originate from the tetragonal platelets.

Journal or Publication Title: Physical Review B
Volume: 96
Number: 18
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
11 Department of Materials and Earth Sciences > Material Science > Structure Research
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ) > Hochleistungsrechner
11 Department of Materials and Earth Sciences > Material Science
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ)
11 Department of Materials and Earth Sciences
Zentrale Einrichtungen
Date Deposited: 20 Nov 2017 08:45
DOI: 10.1103/PhysRevB.96.184107
Official URL: https://doi.org/10.1103/PhysRevB.96.184107
Funders: The authors would like to acknowledge D. Rytz for the synthesis of the investigated single crystal. This work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland. The authors would, also like to thank the Institut Laue-Langevin for the beam time provided and the hospitality. This research project has been supported by the European Commission under the 7th Framework Programme through the “Research Infrastructures” action of the, “Capacities” Programme, NMI3-II Grant No. 283883. This work was funded by the Deutsche Forschungsgemeinschaft (DFG) within the SFB 595 “Electrical Fatigue in Functional Materials” and by the DFG Priority Programme 1599 (AL-578/16). The authors gratefully, acknowledge the computing time granted by the John von Neumann Institute for Computing (NIC) and provided on the supercomputer JURECA [118] at Jülich Supercomputing Centre (JSC). Moreover, computing time was granted on the Lichtenberg-High Performance, Computer at TU Darmstadt.
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