Ferroelectric phase transition in orthorhombic CdTiO3: First-principles studies

Лебедев, А. И.

doi:10.1134/s1063783409040283

Cited by 12 publications

(19 citation statements)

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“…As the energy ratio hν/E 0 = 5.51 exceeds the critical value of 2.419 obtained in Ref. 20, the energy of the lowest vibrational state in a two-well potential appears above the upper point of the energy barrier separating the potential wells, and the ferroelectric ordering is suppressed by zero-point vibrations. Therefore, the only stable phase of RbTaO 3 with the perovskite structure is the cubic phase.…”

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confidence: 97%

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Ferroelectric properties of RbNbO3 and RbTaO3

Лебедев

2015

Phys. Solid State

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Phonon spectra of cubic rubidium niobate and rubidium tantalate with the perovskite structure are calculated from first principles within the density functional theory. Based on the analysis of unstable modes in the phonon spectra, the structures of possible distorted phases are determined, their energies are calculated, and it is shown that R3m is the ground-state structure of RbNbO3. In RbTaO3, the ferroelectric instability is suppressed by zero-point lattice vibrations. For ferroelectric phases of RbNbO3, spontaneous polarization, piezoelectric, nonlinear optical, electro-optical, and other properties as well as the energy band gap in the LDA and GW approximations are calculated. The properties of the rhombohedral RbNbO3 are compared with those of rhombohedral KNbO3, LiNbO3, and BaTiO3. DOI: 10.1134/S1063783415020237 when prepared at atmospheric pressure. To obtain these materials with the perovskite structure, they should be prepared at high pressures (65-90 kbar).6 Due to the difficulties in synthesis of RbNbO 3 and RbTaO 3 with the perovskite structure, the properties of these crystals have been studied very little.The phase diagrams of Rb 2 O-Nb 2 O 5 and Rb 2 OTa 2 O 5 systems were studied in Ref. 7 and 8. RbNbO 3 is formed by the peritectic reaction and decomposes above 964• C. 7 RbTaO 3 decomposes above 600• C probably due to the peritectic reaction too.8 Rubidium-containing ferroelectric materials in the BaNb 2 O 6 -NaNbO 3 -RbNbO 3 system with the tungsten-bronze structure have high electro-optical properties that substantially exceed those of lithium niobate.9,10 In Ref. 11, the possibility of using rubidium niobate and rubidium tantalate for photoelectrochemical decomposition of water was discussed. In Ref. 12, it was proposed to use the delamination of RbTaO 3 structure to produce porous TaO 3 nanomembranes with pore sizes of 1.3×0.6 and 1.1×1.1Å, which can be used for selective filtration of lithium ions.The lack of knowledge on the properties of compounds under consideration appears, in particular, in contradictory data on the ferroelectric properties of RbTaO 3 . For example, the existence of the phase transition at 520 K in the tetragonal phase was reported in Ref. 1, whereas the data of Ref. 6 showed that RbTaO 3 prepared at high pressure has the cubic perovskite (or close to it) structure. At 300 K, the structure of RbNbO 3 is similar to that of the orthorhombic BaTiO 3 , and the data of differential thermal analysis indicate phase transitions in it at 15, 155, and 300• C. 6In this work, the equilibrium structures of RbNbO 3 and RbTaO 3 were determined from first-principles calculations, and spontaneous polarization, dielectric constant, piezoelectric and elastic moduli, nonlinear optical and electro-optical properties as well as the energy band gaps in the LDA and GW approximations were calculated for these crystals.The first-principles calculations were performed within the density functional theory using the ABINIT software.13 The exchange-correlation interaction was described in the loc...

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“…For this purpose, we used the technique proposed in Ref. 20. The energy gain resulting from the transition from the P m3m phase to the R3m phase is E 0 = 1.90 meV and the unstable phonon frequency at the Γ point in the P m3m phase is ν = 84 cm −1 .…”

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Ferroelectric properties of RbNbO3 and RbTaO3

Лебедев

2015

Phys. Solid State

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“…In Ref. 20, a criterion was proposed, which enables, using a set of parameters obtained entirely from first principles, to estimate the stability of a structure with respect to zero-point vibrations. According to this criterion, zero-point vibrations prevent the system to be localized in one of the local minima of the potential if hν/E 0 > 2.419, where ν is the unstable phonon frequency and E 0 is the depth of the local minimum of the potential.…”

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confidence: 99%

Structural instability in BaZrO3 crystals: Calculations and experiment

Лебедев

Sluchinskaya

2013

Phys. Solid State

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Phonon spectrum of cubic barium zirconate is calculated from first principles using the density functional theory. Unstable phonon mode with the R25 symmetry in the phonon spectrum indicates an instability of the cubic structure with respect to rotations of the oxygen octahedra. It is shown that the ground-state structure of the crystal is I4/mcm. In order to find the manifestations of the predicted instability, EXAFS measurements at the Ba LIII-edge are used to study the local structure of BaZrO3 at 300 K. An enhanced value of the Debye-Waller factor for the Ba-O atomic pair (σ 2 1 ∼ 0.015Å2 ) revealed in the experiment is associated with the predicted structural instability. The average amplitude of the thermal octahedra rotation estimated from the measured σ 2 1 value is ∼4 degrees at 300 K. The closeness of the calculated energies of different distorted phases resulting from the condensation of the R25 mode suggests a possible structural glass formation in BaZrO3 when lowering temperature, which explains the cause of the discrepancy between the calculations and experiment.

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“…Note, however, that some subtlety is involved in discriminating between relaxor ferroelectrics and dipole glasses via VogelFulcher equations [108,109]. However, further investigations, especially structural, are required for both since, as with other cryogenic ferroelectric such as CdTiO 3 [110,111] the controversy will continue.…”

Section: Discussionmentioning

confidence: 99%

“…The symmetry change is most probably P 4/mbm-Cmmm. It is inevitable that ferroelastic twin walls parallel to (110) and (1 −1 0) of the parent tetragonal structure will be present in orthorhombic KLT crystals which were synthesized at high temperatures and then cooled through the transition point.…”

Section: Tetragonal Tungsten Bronze-type Structures Including Potmentioning

confidence: 99%

Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5O
Smith
¹
,
Gardner
²
,
Morrison
³

et al. 2018
Phys. Rev. Materials
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We have synthesized ceramic specimens of the tetragonal tungsten bronze K 3 Li 2 Ta 5 O 15 (KLT) and characterized its phase transition via x-ray diffraction, dielectric permittivity, resonant ultrasonic spectroscopy, and heat capacity measurements. The space group of KLT is reported as both P 4/mbm and Cmmm with the orthorhombic distortion occurring when there are higher partial pressures of volatile K and Li used inside the closed crucibles for the solid state synthesis. The data show strong relaxor behavior, with the temperature at which the two dielectric relative permittivity peaks decreasing, with 104 T m1 69 K and 69 T m2 46 K as probe frequency f is reduced from 1 MHz to 316 Hz. F tests show that the data satisfies a Vogel-Fulcher model better than Arrhenius with an extrapolated freezing temperature for ε and ε of T f 1 = +15.8 and −11.8 K and T f 2 = −5.0 and −15.0 K for f → 0 (tending to dc). This difference between T f from real and imaginary values, albeit counterintuitive, is mandatory, according to the theory of Tagantsev. Therefore, by tuning frequency, the transition could be shifted to absolute zero, suggesting KLT has a relaxor-type quantum critical point. In addition, we have reanalyzed the conflicting literature for Pb 2 Nb 2 O 7 pyrochlore which suggests that this also has a relaxor-type quantum critical point since the freezing temperature from the Vogel-Fulcher fitting is below absolute zero. Since the transition temperature evidenced in the dielectric data at approximately 100 kHz shifts below 0 K for very low frequencies, this transition would not be seen with heat capacity data collected in the zero-frequency (dc) limit. Both of these materials show promise for possible new relaxor-type quantum critical points with nonperovskite based structures. DOI: 10.1103/PhysRevMaterials.2.084409 I. THE SEARCH FOR NEW QUANTUM CRITICAL POINT (QCP) FERROELECTRICS INCLUDING RELAXOR QCPSQuantum critical point (QCP) studies of ferroelectrics have been limited to a few crystal structures, emphasizing perovskite oxides. The drive to find new QCPs with ferroelectrics (FEs) are of interest due to the likelihood that they will exhibit novel electrical and thermal properties over wide ranges in temperature and tuning parameters, similar to what is seen in more widely studied magnetic counterparts. However, as the dynamical exponent is 1 for displacive FE rather than 3 for itinerant ferromagnets, the understanding and modeling of their properties are likely to be more complex, since real systems can exceed the upper and lower critical dimensionality [1]. For a QCP to occur, the transition should be driven by quantum fluctuations rather than classical fluctuations, and such quantum fluctuations tend to dominate in a region just above 0 K. Interest in ferroelectric quantum critical points has grown rapidly in the past several years, with emphasis upon perovskites [1,2] and several other materials, including hexaferrites [3][4][5][6] and organic or molecular crystals [7][8][9][10]. However, the QCPs studied thus ...

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Ferroelectric phase transition in orthorhombic CdTiO3: First-principles studies

Cited by 12 publications

References 19 publications

Ferroelectric properties of RbNbO3 and RbTaO3

Ferroelectric properties of RbNbO3 and RbTaO3

Structural instability in BaZrO3 crystals: Calculations and experiment

Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5O
Smith
¹
,
Gardner
²
,
Morrison
³

et al. 2018
Phys. Rev. Materials
3
0
2
0
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Ferroelectric phase transition in orthorhombic CdTiO3: First-principles studies

Cited by 12 publications

References 19 publications

Ferroelectric properties of RbNbO3 and RbTaO3

Ferroelectric properties of RbNbO3 and RbTaO3

Structural instability in BaZrO3 crystals: Calculations and experiment

Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5OSmith1, Gardner2, Morrison3 et al. 2018Phys. Rev. Materials3020View full textAdd to dashboardCite

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Quantum critical points in ferroelectric relaxors: Stuffed tungsten bronze K3Li2Ta5O
Smith
¹
,
Gardner
²
,
Morrison
³

et al. 2018
Phys. Rev. Materials
3
0
2
0
View full text Add to dashboard Cite