First-Principles Determination of Chain-Structure Instability in KNb<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Yu, Rici; Krakauer, Henry

doi:10.1103/physrevlett.74.4067

Cited by 166 publications

(129 citation statements)

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“…Further phonon analysis (17,18) on BaTiO 3 revealed two-dimensional character in the Brillouin zone, which corresponds to chains oriented along ͗100͘ directions of displaced Ti atoms. Such character had been found in KNbO 3 (19), a material with the same phase diagram as BaTiO 3 . In addition, the BaTiO 3 phonon analysis showed that X point instability is slightly less unstable than Gamma point in BaTiO 3 , implying a ferroelectric relaxation could lead to a lower-energy structure than an antiferroelectric relaxation.…”

mentioning

confidence: 96%

The ferroelectric and cubic phases in BaTiO ₃ ferroelectrics are also antiferroelectric

Zhang

Çağın

Goddard

2006

Proc. Natl. Acad. Sci. U.S.A.

130

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Using quantum mechanics (QM, Density Functional Theory) we show that all four phases of barium titanate (BaTiO 3) have local Ti distortions toward ͗111͘ (an octahedral face). The stable rhombohedral phase has all distortions in phase (ferroelectric, FE), whereas higher temperature phases have antiferroelectric coupling (AFE) in one, two, or three dimensions (orthorhombic, tetragonal, cubic). This FE-AFE model from QM explains such puzzling aspects of these systems as the allowed Raman excitation observed for the cubic phase, the distortions toward ͗111͘ observed in the cubic phase using x-ray fine structure, the small transition entropies, the heavily damped soft phonon modes, and the strong diffuse x-ray scattering in all but the rhombohedral phase. In addition, we expect to see additional weak Bragg peaks at the face centers of the reciprocal lattice for the cubic phase. Similar FE-AFE descriptions are expected to occur for other FE materials. Accounting for this FE-AFE nature of these phases is expected to be important in accurately simulating the domain wall structures, energetics, and dynamics, which in turn may lead to the design of improved materials.barium titanate ͉ phase transition F erroelectric (FE) materials have broad applications in transducers, actuators, capacitors, and memories. Particularly well studied is BaTiO 3 , which has rhombohedral (R), orthorhombic (O), tetragonal (T), and cubic (C) phases. However, the microscopic nature of the phases and transitions in BaTiO 3 remains uncertain. A popular model in history is the displacive model (1, 2), in which the equilibrium position of each Ti atom is in the middle of the oxygen octahedron for C, but displaced microscopically in the ͗111͘, ͗011͘, or ͗001͘ macroscopic polarization directions for the R, O, and T ferroelectric phases, respectively. However, this displacive model Y Predicts that first-order Raman excitation should vanish in the cubic phase due to the microscopic inversion symmetry, contradicting experiments (3). Y Contradicts the x-ray fine structure (XAFS) experiments (4) that show that the Ti atoms are displaced along various of the eight possible ͗111͘ directions in all phases. Y Does not explain the heavily damped but nonzero frequency for the soft modes at the C to T transition observed by infrared reflectivity (IR) experiments (5). Y Does not explain the strong diffuse x-ray scattering observed in all but the rhombohedral phase.To explain these failures of the displacive model, a spontaneous symmetry breaking has been hypothesized to occur in these systems (6). Thus Berserker (7), Comes et al. (8) and Chaves et al. (9) introduced the order-disorder eight-site model (8OD), in which all Ti atoms are microscopically located in one of eight potential minima along the ͗111͘ directions for all crystal phases. As in the displacive model, 8OD assumes that the low temperature R phase has all Ti atoms distorted in the same direction. As temperature increases, 8OD assumes disorder in the polarization along one or more crystal directions...

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mentioning

confidence: 96%

The ferroelectric and cubic phases in BaTiO ₃ ferroelectrics are also antiferroelectric

Zhang

Çağın

Goddard

2006

Proc. Natl. Acad. Sci. U.S.A.

130

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“…Overall, both B3LYP and GGA yield similar agreement with experiment, while RHF is significantly worse. Comparisons for the cubic and ferroelectric P4mm tetragonal BaTiO 3 phases should keep in mind evidence for static and/or motional disorder of local structures suggested by experiment 54,70,71 and theory, 72,73 since the present calculations were performed for ordered crystalline structures.…”

Section: Comparison Of Oxygen Chemical Shifts With Experimentsmentioning

confidence: 99%

High sensitivity of O17 NMR to p-d hybridization in transition metal perovskites: First principles calculations of large anisotropic chemical shielding

Pechkis

Krakauer

2009

The Journal of Chemical Physics

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A first principles embedded cluster approach is used to calculate O chemical shielding tensors, σ, in prototypical transition metal oxide ABO3 perovskite crystals. Our principal findings are 1) a large anisotropy ofσ between deshielded σx ≃ σy and shielded σz components (z along the Ti-O bond); 2) a nearly linear variation, across all the systems studied, of the isotropic σiso and uniaxial σax components, as a function of the B-O-B bond asymmetry. We show that the anisotropy and linear variation arise from large paramagnetic contributions to σx and σy due to virtual transitions between O(2p) and unoccupied B(nd) states. The calculated isotropic δiso and uniaxial δax chemical shifts are in good agreement with recent BaTiO3 and SrTiO3 single crystal 17 O NMR measurements. In PbTiO3 and PbZrO3, calculated δiso are also in good agreement with NMR powder spectrum measurements. In PbZrO3, δiso calculations of the five chemically distinct sites indicate a correction of the experimental assignments. The strong dependence ofσ on covalent O(2p)-B(nd) interactions seen in our calculations indicates that 17 O NMR spectroscopy, coupled with first principles calculations, can be an especially useful tool to study the local structure in complex perovskite alloys.

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“…The symmetry of the phonons determines the symmetry of the low temperature structure. This approach has been successfully used in the study of minerals [3,4,5] and ferroelectric materials [6,7,8,9] and has been extended to shape memory alloys in our previous study of NiTi [10].…”

Section: Introductionmentioning

confidence: 99%

First-principles study of the structural energetics of PdTi and PtTi

2003

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The structural energetics of PdTi and PtTi have been studied using first-principles densityfunctional theory with pseudopotentials and a plane-wave basis. We predict that in both materials, the experimentally reported orthorhombic B19 phase will undergo a low-temperature phase transition to a monoclinic B19 ′ ground state. Within a soft-mode framework, we relate the B19 structure to the cubic B2 structure, observed at high temperature, and the B19 ′ structure to B19 via phonon modes strongly coupled to strain. In contrast to NiTi, the B19 structure is extremely close to hcp. We draw on the analogy to the bcc-hcp transition to suggest likely transition mechanisms in the present case.

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First-Principles Determination of Chain-Structure Instability in KNbO3

Cited by 166 publications

References 20 publications

The ferroelectric and cubic phases in BaTiO ₃ ferroelectrics are also antiferroelectric

The ferroelectric and cubic phases in BaTiO ₃ ferroelectrics are also antiferroelectric

High sensitivity of O17 NMR to p-d hybridization in transition metal perovskites: First principles calculations of large anisotropic chemical shielding

First-principles study of the structural energetics of PdTi and PtTi

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First-Principles Determination of Chain-Structure Instability in KNbO3

Cited by 166 publications

References 20 publications

The ferroelectric and cubic phases in BaTiO 3 ferroelectrics are also antiferroelectric

The ferroelectric and cubic phases in BaTiO 3 ferroelectrics are also antiferroelectric

High sensitivity of O17 NMR to p-d hybridization in transition metal perovskites: First principles calculations of large anisotropic chemical shielding

First-principles study of the structural energetics of PdTi and PtTi

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The ferroelectric and cubic phases in BaTiO ₃ ferroelectrics are also antiferroelectric

The ferroelectric and cubic phases in BaTiO ₃ ferroelectrics are also antiferroelectric