Manifestation of Polaronic States in Ferroelectric Relaxor PMN

Vikhnin, V. S.; Kapphan, S.; Kislova, I. L.; Eglitis, R. I.; Markovin, P. A.

doi:10.1080/00150190390206130

Cited by 3 publications

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“…Actually, the glassy-state versus nanodomains model is still debated and no consensus or satisfactory description of the real structure currently exists. As detailed in some reviews [3,[13][14][15], other concepts have also been considered to explain the peculiar properties of PMN, including chemically ordered regions [16] possessing large dielectric response [17,18], overbonded oxygen ions [19], polaronic mechanism [20,21], and the coexistence of ferroelectric and antiferroelectric couplings [22]. It is also unclear if the recent mechanism that has been determined from first-principles-based calculations on the homovalent Ba(Zr,Ti)O 3 (BZT) relaxor ferroelectric-that is the coexistence within the same material of ferroelectrically active and ferroelectrically inactive (silent) ions [23]-holds for PMN.…”

Section: Introductionmentioning

confidence: 99%

Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

et al. 2015

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An atomistic numerical scheme is developed and used to study the prototype of relaxor ferroelectrics, that is PbMg 1/3 Nb 2/3 O 3 (PMN), at finite temperatures. This scheme not only reproduces known complex macroscopic properties of PMN, but also provides a deep microscopic insight into this puzzling system. In particular, relaxor properties of PMN are found to originate from the competition between (1) random electric fields arising from the alloying of Mg and Nb ions belonging to different columns of the Periodic Table within the same sublattice; (2) the simultaneous condensation of several off-center k points as a result of a specific short-range, antiferroelectriclike interaction between lead-centered dipoles; and (3) ferroelectriclike interactions. Such origins contrast with those recently proposed for the homovalent Ba(Zr,Ti)O 3 solid solution, despite the fact that these two materials have similar macroscopic properties-which therefore leads to a comprehensive understanding of relaxor ferroelectrics.

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Section: Introductionmentioning

confidence: 99%

Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

et al. 2015

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“…In INDO calculations we have used a periodic (large unit cell) model with the primitive KTO unit cell volume extended by a factor of 3×3×3 = 27. As a result, the following structure of CTVE in KTO was obtained: the CTVE has a triad geometrical structure [12,14,15] with a rather strong vibronic energy gain (∼ 2.71 eV). The latter is connected to the appearance of a hole polaron on one oxygen ion which has a displacement of 5.2% of the lattice constant towards the first active Ta ion, on which the electronic polaron is partly located.…”

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“…The CTVE in ABO 3 ferroelectric oxides with mixed ionic-covalent type of chemical bonding (including KTO, KNbO 3 (KNO), STO) are new topics in this field. They consist of the correlated pairs or/and triads of electronic and hole polarons [6][7][8][9][10][11][12][13][14][15]. CTVE formation is possibile due to the electron and hole polaron vibronic interaction enhanced by the charge transfer.…”

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“…Such type of investigation was developed in the present work by the INDO method. Let us briefly discuss a recent analysis [12,14,15] of a single CTVE which was done by the INDO method [18][19][20][21][22].…”

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“…Additionally, we have evaluated the CTVE phase state constructed from triplet spin states of individual CTVE. The latter is based on the INDO calculation of the singlet-triplet splitting for an individual CTVE [15] and on the assumption that CTVE-CTVE spin-spin interaction does not change such a spin order. While this evaluation confirms that the triplet spin state is a real ground state of an individual CTVE in KTO and, probably, related systems, the CTVE-CTVE spin-spin interaction effect can lead to many-variant magnetic structures for the CTVE phase.…”

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A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons

Vikhnin¹,

Eglitis

Kapphan

et al. 2001

Europhys. Lett.

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It is shown, by means of Hartree-Fock-type calculations using the intermediate neglect of the differential overlap (INDO) method, that polaronic-type charge transfer vibronic excitons (CTVE) in ferroelectric oxides could lead to the formation of a new phase. The ground-state energy of this phase of strongly correlated CTVE lies within an optical gap of pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as ferroelectric and antiferromagnetic ordering. It is shown also that clusters of the CTVE phase being stabilized by oxygen vacancies could be responsible for the unusually strong optical Second Harmonic Generation (SHG) in nominally pure incipient ferroelectrics, like KTaO3 (KTO) and SrTiO3 (STO), especially in the case of SHG induced by an external electric field. Another experimental manifestation of CTVE is related to a drastic red shift with temperature of the fundamental absorption (FA) edge in ferroelectric oxides SBN and KTO observed at high temperatures. This effect could be explained by thermal population of a low-lying bottom part of an additional valence band induced by the CTVE phase.Introduction. -A study of polaronic states in oxygen-octahedrical perovskites is one of the important topics of modern solid-state physics and chemistry [1][2][3][4][5]. The CTVE in ABO 3 ferroelectric oxides with mixed ionic-covalent type of chemical bonding (including KTO, KNbO 3 (KNO), STO) are new topics in this field. They consist of the correlated pairs or/and triads of electronic and hole polarons [6][7][8][9][10][11][12][13][14][15]. CTVE formation is possibile due to the electron and hole polaron vibronic interaction enhanced by the charge transfer. Such an effect is partly connected to the appearance of degenerate or pseudo-degenerate states of active ions in the final, CTVE state. The above-mentioned increase of the vibronic interaction induced by charge transfer leads to the formation of a new potential well of the potential for the CTVEactive vibration. The system's stability with such a new vibronic minimum is controlled by the potential barrier which is mainly of a vibronic origin, because electron-hole Coulomb attraction is strongly screened by the polarization effect in the ferroelectric soft matrices discussed. That is why this exciton state is called CTVE [6,7]. The CTVE state can be considered as a bipolaron comprising a pair of spatially correlated polaronic electron and polaronic hole. Their correlation is controlled by the "negative-U " effect. Moreover, this is

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Manifestation of Polaronic States in Ferroelectric Relaxor PMN

Cited by 3 publications

References 0 publications

Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons

Polar modes in relaxorPbMg1∕3Nb2∕3O3
Hehlen
¹
,
Hlinka
²

2007
Phys. Rev. B
20
2
13
0
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Manifestation of Polaronic States in Ferroelectric Relaxor PMN

Cited by 3 publications

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Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

Finite-temperature properties of the relaxorPbMg1/3Nb2/3O3from atomistic simulations

A new phase in ferroelectric oxides: The phase of charge transfer vibronic excitons

Polar modes in relaxorPbMg1∕3Nb2∕3O3Hehlen1, Hlinka2 2007Phys. Rev. B202130View full textAdd to dashboardCite

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Polar modes in relaxorPbMg1∕3Nb2∕3O3
Hehlen
¹
,
Hlinka
²

2007
Phys. Rev. B
20
2
13
0
View full text Add to dashboard Cite