Off-center displacement of the Nb ions below and above the ferroelectric phase transition of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">KTa</mml:mi></mml:mrow><mml:mrow><mml:mn>0.91</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Nb</mml:mi></mml:mrow><mml:mrow><mml:mn>0.09</mml:mn></

Hanske-Petitpierre, O.; Yacoby, Y.; León, J.; Stern, Edward A.; Rehr, J. J.

doi:10.1103/physrevb.44.6700

Cited by 155 publications

(80 citation statements)

References 26 publications

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“…Of special interest here are the experimental conclusions that in all the phases, the Ti ion is instantly displaced in the trigonal direction in disagreement with displacive theories in which the metal off-center displacement occurs as a result of the phase transition to the ferroelectric phases. This basic conclusion was confirmed directly by a variety experimental methods, noticeable EXAFS, [36][37][38] EPR experiments with probing ions, [39][40][41] NMR, 42,43 neutron scattering, 44 etc. Not only is the Ti ion displaced along the [111] type direction in the paraelectric phase where the averaged symmetry is cubic, but it is as well displaced in this trigonal direction in the tetragonal phase where the crystal symmetry and the macroscopic polarization are tetragonal.…”

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confidence: 77%

Pseudo Jahn–Teller effect in the origin of enhanced flexoelectricity

Берсукер

2015

Applied Physics Letters

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The controversy between the theory and experiment in explaining the origin of enhanced flexoelectricity is removed by taking into account the pseudo Jahn-Teller effect (PJTE) which, under certain conditions, creates local dipolar distortions of dynamic nature, resonating between two or more equivalent orientations. The latter become nonequivalent under a strain gradient thus producing enhanced flexoelectricity: it is much easier to orient ready-made dipoles than to polarize an ionic solid. For BaTiO3, the obtained earlier numerical data for the adiabatic potential energy surface in the space of dipolar displacements in the Ti centers were used to estimate the flexoelectric coefficient f in the paraelectric phase in a one-dimensional model with the strain gradient along the [111] direction: f = −0.43 × 10−6 Cm−1. This eliminates the huge contradiction between the experimental data of f ∼ μ Cm−1 for this case and the theoretical predictions (without the PJTE) of 3–4 orders-of-magnitude smaller values. Enhanced flexoelectricity is thus expected in solids with a sufficient density of centers that have PJTE induced dipolar instabilities. It explains also the origin of enhanced flexoelectricity observed in other solids, noticeable containing Nb perovskite centers which are known to have a PJTE instability, similar to that of Ti centers. The SrTiO3 crystal as a virtual ferroelectric in which the strain gradient eases the condition of PJTE polar instability is also discussed.

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confidence: 77%

Pseudo Jahn–Teller effect in the origin of enhanced flexoelectricity

Берсукер

2015

Applied Physics Letters

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“…This technique has been proven to be a powerful tool to analyze the local distortions in ferroelectric perovskites (e. g. Refs. 28,29,30,31). On the other hand, only a few EXAFS studies have been reported for relaxors yet 32,33,34,35,36 .…”

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confidence: 99%

EXAFS study of lead-free relaxor ferroelectricBaTi1−xZrxO3at the Zr
Laulhé
¹
,
Hippert
²
,
Kreisel
³

et al. 2006
Phys. Rev. B
104
2
65
1
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Extended X-ray absorption fine structure (EXAFS) experiments at the Zr K-edge were carried out on perovskite relaxor ferroelectrics BaTi1−xZrxO3 (BTZ) (x = 0.25, 0.30, 0.35), and on BaZrO3 for comparison. Structural information up to 4.5Å around the Zr atoms is obtained, revealing that the local structure differs notably from the average Pm3m cubic structure deduced from X-ray diffraction. In particular, our results show that the distance between Zr atoms and their first oxygen neighbors is independent of the Zr substitution rate x and equal to that measured in BaZrO3, while the X-ray cubic cell parameter increases linearly with x. Furthermore, we show that the Zr atoms tend to segregate in Zr-rich regions. We propose that the relaxor behavior in BTZ is linked to random elastic fields generated by this particular chemical arrangement, rather than to random electric fields as is the case in most relaxors.

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“…According to x-ray diffraction ͑XRD͒ experiments, a structural phase transition to a cubic structure occurred in this case. [4][5][6] Recently, we studied the composition resulting from the substitution of the Pb ion by La in the Pb 1−x La x TiO 3 system for x ranging from 0 to 30 at. % using XAS and XRD techniques.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of Pb1−xLaxTiO3 ferroelectric materials from Ti 2p and O 1s soft x-ray absorption spectroscopy

Mastelaro

Neves

Lázaro

et al. 2006

Journal of Applied Physics

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The electronic structure of Pb 1−x La x TiO 3 ͑PLT͒ compounds for x ranging from 0 to 30 at. % of La is investigated by means of soft x-ray absorption near edge structure ͑XANES͒ at the Ti L 3,2 and O K edges. The greatest modification in the structure of the Ti 2p XANES spectra of the PLT compounds is observed in the region of the high energy peak of the L 3 edge ͑e g states͒, which exhibits a splitting in the undoped sample. As the amount of lanthanum increases, this splitting becomes less pronounced. This modification is interpreted as a decrease in the degree of disorder of titanium atoms, which is correlated to the substitution of Pb by La atoms. The structural changes observed at the low energy peaks of the O K-edge XANES spectra of the PLT compounds may be interpreted in terms of hybridization between O 2p, Ti 3d, and Pb 6p orbitals. A decrease in the degree of hybridization observed as Pb atoms are replaced by La atoms may be related to the differences in the ferroelectric properties observed between x = 0.0 and x = 0.30 compounds.

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Off-center displacement of the Nb ions below and above the ferroelectric phase transition ofKTa0.91Nb0.09

Cited by 155 publications

References 26 publications

Pseudo Jahn–Teller effect in the origin of enhanced flexoelectricity

Pseudo Jahn–Teller effect in the origin of enhanced flexoelectricity

EXAFS study of lead-free relaxor ferroelectricBaTi1−xZrxO3at the Zr
Laulhé
¹
,
Hippert
²
,
Kreisel
³

et al. 2006
Phys. Rev. B
104
2
65
1
View full text Add to dashboard Cite

Electronic structure of Pb1−xLaxTiO3 ferroelectric materials from Ti 2p and O 1s soft x-ray absorption spectroscopy

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Off-center displacement of the Nb ions below and above the ferroelectric phase transition ofKTa0.91Nb0.09

Cited by 155 publications

References 26 publications

Pseudo Jahn–Teller effect in the origin of enhanced flexoelectricity

Pseudo Jahn–Teller effect in the origin of enhanced flexoelectricity

EXAFS study of lead-free relaxor ferroelectricBaTi1−xZrxO3at the ZrLaulhé1, Hippert2, Kreisel3 et al. 2006Phys. Rev. B1042651View full textAdd to dashboardCite

Electronic structure of Pb1−xLaxTiO3 ferroelectric materials from Ti 2p and O 1s soft x-ray absorption spectroscopy

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Product

Resources

About

EXAFS study of lead-free relaxor ferroelectricBaTi1−xZrxO3at the Zr
Laulhé
¹
,
Hippert
²
,
Kreisel
³

et al. 2006
Phys. Rev. B
104
2
65
1
View full text Add to dashboard Cite