Local structural changes in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">KNbO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>under high pressure

Frenkel, Anatoly I.; Wang, F.M.; Kelly, Shelly D.; Ingalls, R.; Haskel, D.; Stern, Edward A.; Yacoby, Y.

doi:10.1103/physrevb.56.10869

Cited by 57 publications

(40 citation statements)

References 28 publications

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“…Let us recall that for an atom of scattering factor f displaced by u, the total diffuse scattering intensity is proportional to f 2 u 2 . u 2 being similar in both compounds [27,28], the intensity of the KNbO 3 DL is clearly due to the large atomic number of Nb. Moreover, INS results have shown that despite similar anisotropy, the TA mode is less dispersive in KNbO 3 than in BaTiO 3 (see Fig.…”

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confidence: 80%

High-Pressure Study of X-Ray Diffuse Scattering in Ferroelectric Perovskites

et al. 2007

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We present a high-pressure x-ray diffuse scattering study of the ABO3 ferroelectric perovskites BaTiO3 and KNbO3. The well-known diffuse lines are observed in all the phases studied. In KNbO3, we show that the lines are present up to 21.8 GPa, with constant width and a slightly decreasing intensity. At variance, the intensity of the diffuse lines observed in the cubic phase of BaTiO3 linearly decreases to zero at ∼ 11 GPa. These results are discussed with respect to x-ray absorption measurements, which leads to the conclusion that the diffuse lines are only observed when the B atom is off the center of the oxygen tetrahedron. The role of such disorder on the ferroelectric instability of perovskites is discussed. Because of the simplicity of their structure and their actual or potential applications, perovskites ABO 3 and their derivatives are amongst the most studied compounds in solid state science. Perovskites stabilize a large variety of states such as superconductivity, ferroelectricity (FE) and multiferroism, but despite decades of studies, the mechanisms of these transitions are still a matter of debate [1]. This is the case of the oxygen perovskites such as SrTiO 3 and KTaO 3 , which only exhibit incipient FE, while PbTiO 3 , BaTiO 3 and KNbO 3 stabilize this instability in well defined series of FE transitions.Upon heating at ambient pressure, barium titanate and potassium niobate undergo the same famous sequence of rhomboedric-orthorhombic-tetragonal-cubic (R-O-T-C) first-order phase transitions [2,3]. During this sequence, the polarization changes direction from the [111], to the [110] and [100] pseudo-cubic directions, before vanishing above the Curie temperature T C in the cubic phase. The mechanism of this sequence of phase transition has been often discussed from two limiting cases: the soft mode -or displacive -theory, in which a transverse optical (TO) mode frequency gradually soften when approaching the phase transition [4], and an order-disorder scenario [5], in which some atoms lying on symmetryequivalent sites, order on preferential ones. In fact, current theories favor an intermediate situation, in which soft phonons and disorder play a role [6,7].Pressure has proven to be an essential parameter to study phase transitions in perovskites [8]. Because applying pressure results in a symmetrization of chemical bonds, drastic effects on order-disorder phase transitions are expected. Indeed, the same sequence of phase transitions is observed as a function of pressure in KNbO 3 and BaTiO 3 [9]. At 300 K, FE is lost at 10 GPa (2 GPa) and is no more observed at low temperature above ∼ 26 GPa (∼ 6.5 GPa) in KNbO 3 (BaTiO 3 ). The existence of the O-T transition under pressure has been questioned in KNbO 3 [10], while in other studies its transition pressure was found at 6 GPa [11] or 8.5 GPa [9]. In this letter, we will show that high pressure x-ray diffuse scattering measurements give a unique opportunity to study the transitions and the FE instability as a function of the nature and the position of...

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confidence: 80%

High-Pressure Study of X-Ray Diffuse Scattering in Ferroelectric Perovskites

et al. 2007

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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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“…We now examine a fully distorted tetragonal phase, which enables us to compare the calculated results with experimental data. The tetragonal perovskite phase is the stable polymorph of BaTiO 3 and KNbO 3 , in a temperature range between the cubic and orthorhombic modifications (393K>T>278 K in BaTiO 3 [100], 708K>T>498 K in KNbO 3 [101]). …”

Section: Tetragonal Phasementioning

confidence: 99%