Influence of tetragonal platelets on the dielectric permittivity of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>0.964</mml:mn><mml:msub><mml:mi>Na</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>Bi</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi>TiO</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mtext>−</mml:mtext><mml:mn>0.036</mml:mn><mml:msub><mml:mi>Ba

Pforr, Florian; Major, M.; Donner, W.; Stuhr, U.; Roessli, B.

doi:10.1103/physrevb.94.014105

Cited by 9 publications

(11 citation statements)

References 74 publications

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“…In the scenario of continuous octahedral tilting disorder, the cubic phase recently revealed by NMR experiments13 could be regarded as a smooth interface between regions of more marked tilting or regions with different tilt orientation40. Although this cubic content cannot be detected with 3QMAS, as this experiment is “blind” for sites with vanishingly small EFGs, a larger content of the cubic phase is reported13 for samples with higher degree of local disorder (e.g.…”

Section: Discussionmentioning

confidence: 82%

Reconciling Local Structure Disorder and the Relaxor State in (Bi1/2Na1/2)TiO3-BaTiO3

Groszewicz

Gröting

Breitzke

et al. 2016

Sci Rep

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Lead-based relaxor ferroelectrics are key functional materials indispensable for the production of multilayer ceramic capacitors and piezoelectric transducers. Currently there are strong efforts to develop novel environmentally benign lead-free relaxor materials. The structural origins of the relaxor state and the role of composition modifications in these lead-free materials are still not well understood. In the present contribution, the solid-solution (100-x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-xBT), a prototypic lead-free relaxor is studied by the combination of solid-state nuclear magnetic resonance (NMR) spectroscopy, dielectric measurements and ab-initio density functional theory (DFT). For the first time it is shown that the peculiar composition dependence of the EFG distribution width (ΔQISwidth) correlates strongly to the dispersion in dielectric permittivity, a fingerprint of the relaxor state. Significant disorder is found in the local structure of BNT-xBT, as indicated by the analysis of the electric field gradient (EFG) in 23Na 3QMAS NMR spectra. Aided by DFT calculations, this disorder is attributed to a continuous unimodal distribution of octahedral tilting. These results contrast strongly to the previously proposed coexistence of two octahedral tilt systems in BNT-xBT. Based on these results, we propose that considerable octahedral tilt disorder may be a general feature of these oxides and essential for their relaxor properties.

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Section: Discussionmentioning

confidence: 82%

Reconciling Local Structure Disorder and the Relaxor State in (Bi1/2Na1/2)TiO3-BaTiO3

Groszewicz

Gröting

Breitzke

et al. 2016

Sci Rep

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show abstract

“…Bearing the cation-order dependence of the ground state tilt structure in mind, it appears reasonable to assume that the coexistence of tetragonal platelets and a rhombohedral matrix in NBT-BT results from locally different cation order, as proposed in Ref. 63. Further simulation studies have confirmed that the cation order has a significant impact on the tilt defect energies and tilt dynamics, too.…”

Section: Introductionmentioning

confidence: 73%

“…63. Spectra from 10 K to 300 K were collected at IN8 110 (ILL, France) using the same 0.964Na 1/2 Bi 1/2 TiO 3 − 0.036BaTiO 3 single crystal sample, 63 mounted in an orange cryostat using bent Al sheet and VGE-7031 varnish (Cryophysics GmbH, Darmstadt). The incident and scattered wavevectors were defined using a Si monochromator and double focusing pyrolytic graphite analyzer.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

“…QENS spectra were measured at one superlattice reflection that is due to in-phase tilting [Q = 1 2 (310)] and one that is due to anti-phase tilting [ 1 2 (311)]. 63 Reciprocal space coordinates are given with respect to the single perovskite unit cell with a ≈ 3.9Å. Nine data sets above and five at or below room temperature (RT) were collected at each Q point.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

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Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na1/2Bi1/2TiO3−0.036
Pforr
¹
,
Meyer
²
,
Major
³

et al. 2017
Phys. Rev. B
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0
2
0
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The local dynamics of the lead-free relaxor 0.964Na 1/2 Bi 1/2 TiO 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 [F. Pforr et al., Phys. Rev. B 94, 014105 (2016)]. To investigate their dynamics, ab initio molecular dynamics simulations were carried out using Na 1/2 Bi 1/2 TiO 3 with 001 cation order as a simple model system for the tetragonal platelets in NBT-3.6BT. Similarly, 111-ordered Na 1/2 Bi 1/2 TiO 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 timescale 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.

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“…Two possible phase transformations were suggested: a “direct” transition from the rhombohedral to the tetragonal phase and an “indirect” transition via an intermediate orthorhombic phase . In each of these transitions it appears that several phases are present simultaneously over a wide temperature range (as in NBT‐BT), making the phase transitions “diffuse.”…”

Section: Introductionmentioning

confidence: 99%

Phase transformations in the relaxor Na_1/2Bi_1/2TiO₃ studied by means of density functional theory calculations

2017

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The relaxor material Na 1/2 Bi 1/2 TiO 3 (NBT) is an important basis for the development of lead-free piezoceramics, but still many features of this material are not well understood. Here, we study the kinetics of phase transformations by octahedral tilts and A-cation displacements in NBT by means of density functional theory calculations, employing ab initio molecular dynamics and nudged elastic band calculations. Our results show that the energetic differences between the low temperature rhombohedral, intermediate orthorhombic and other metastable phases are close to the room temperature thermal energy. Therefore, it is likely that above room temperature, several octahedral tilt patterns are present simultaneously on the local scale, just because of thermal vibration of the oxygen ions. Octahedral tilt transformations and A-cation displacements show similarly high energy barriers, however, since the vibrational frequency of oxygen is higher, tilt transformations occur more frequently. Further, tilt transformations in which the oxygen octahedra get deformed the least are more probable to occur. We also find that the chemical A-cation order affects energy barriers, influences the coupling between rotational and displacive modes and determines the stability of certain octahedral tilt orders. We conclude that the so-called polar nanoregions in this material result from local octahedral tilt transformations and subsequent A-cation displacements, which are driven by thermal vibration and are mediated by the underlying chemical order.

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Influence of tetragonal platelets on the dielectric permittivity of0.964Na1/2Bi1/2TiO3−0.036Ba

Cited by 9 publications

References 74 publications

Reconciling Local Structure Disorder and the Relaxor State in (Bi1/2Na1/2)TiO3-BaTiO3

Reconciling Local Structure Disorder and the Relaxor State in (Bi1/2Na1/2)TiO3-BaTiO3

Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na1/2Bi1/2TiO3−0.036
Pforr
¹
,
Meyer
²
,
Major
³

et al. 2017
Phys. Rev. B
Self Cite
8
0
2
0
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Phase transformations in the relaxor Na_1/2Bi_1/2TiO₃ studied by means of density functional theory calculations

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Influence of tetragonal platelets on the dielectric permittivity of0.964Na1/2Bi1/2TiO3−0.036Ba

Cited by 9 publications

References 74 publications

Reconciling Local Structure Disorder and the Relaxor State in (Bi1/2Na1/2)TiO3-BaTiO3

Reconciling Local Structure Disorder and the Relaxor State in (Bi1/2Na1/2)TiO3-BaTiO3

Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na1/2Bi1/2TiO3−0.036Pforr1, Meyer2, Major3 et al. 2017Phys. Rev. BSelf Cite8020View full textAdd to dashboardCite

Phase transformations in the relaxor Na1/2Bi1/2TiO3 studied by means of density functional theory calculations

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Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na1/2Bi1/2TiO3−0.036
Pforr
¹
,
Meyer
²
,
Major
³

et al. 2017
Phys. Rev. B
Self Cite
8
0
2
0
View full text Add to dashboard Cite

Phase transformations in the relaxor Na_1/2Bi_1/2TiO₃ studied by means of density functional theory calculations