Phase transitions sequence in pyrochlore Cd2Nb2O7 studied by IR reflectivity

Buixaderas, E.; Kamba, S.; Petzelt, J.; Savinov, M.; Колпакова, Н. Н.

doi:10.1007/s100510170344

Cited by 45 publications

(34 citation statements)

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“…Quite commonly additional lattice modes appear in the phonon spectra, or a dramatic redistribution of the spectral weight between several resonances takes place provided the system reduces its symmetry in the charge-ordered regime. 18 We failed to detect any of these effects. Furthermore, a detailed analysis of the x-ray diffraction data did not produce any indications for structural changes at TϽT MIT .…”

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confidence: 82%

Searching for the Slater transition in the pyrochloreCd2Os2O7<

2002

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Infrared reflectance measurements were made on the single crystal pyrochlore Cd 2 Os 2 O 7 in order to examine the transformations of the electronic structure and crystal lattice across the boundary of the metal-insulator transition ͑MIT͒ at T MIT ϭ226 K. All predicted IR active phonons are observed in the conductivity over all temperatures and the oscillator strength is found to be temperature independent. These results indicate that charge ordering plays only a minor role in the MIT and that the transition is strictly electronic in nature. The conductivity shows the clear opening of a gap with 2⌬ϭ5.2k B T MIT . The gap opens continuously, with a temperature dependence similar to that of Bardeen-Cooper-Schrieffer ͑BCS͒ superconductors, and the gap edge having a distinct ()ϳ 1/2 dependence. All of these observables support the suggestion of a Slater transition in Cd 2 Os 2 O 7 .Mott's classic paper, 1 published over half a century ago, has triggered extensive research on correlated electron systems which undergo a MIT. Both Mott and Hubbard 2 have suggested that for systems at half filling, the Coulomb repulsion between electrons could split the band, thus yielding an insulator. Alternatively, Slater in 1951 suggested that antiferromagnetic order alone could produce an insulator by a doubling of the magnetic unit cell. 3 While there are numerous examples of Slater/spin-density-wave ͑SDW͒ insulators in the realm of one-dimensional ͑1D͒ conductors, 4,5 the experimental situation at higher dimensions is less clear. Impossibility of the Slater state in the 2D regime has been recently argued based on dynamical cluster approximation calculations. 6 For 3D solids, spin ordering alone usually generates an energy gap corrupting only a fraction of the Fermi surface so that metallic conductivity persists. 7 In this context, the metal-insulator transition in the 3D pyrochlore Cd 2 Os 2 O 7 is exceptionally intriguing since transport and magnetic properties across the MIT boundary appear to be in accord with the Slater mechanism. 8 In this paper we report on our spectroscopic studies of the MIT in Cd 2 Os 2 O 7 . Our analysis of the infrared data reveals that the transition into the insulating state is driven solely by the electronic interactions without significant involvement of the crystal lattice. We discuss new facets of the spin-driven insulating state in a 3D material.The pyrochlore Cd 2 Os 2 O 7 was first characterized by Sleight et al. 9 The metal-insulator transition in the resistivity has been found to occur at the same temperature, Ӎ226 K, as the antiferromagnetic transition in susceptibility measurements. No evidence of concurrent structural changes were detected through x-ray diffraction ͑XRD͒ analysis. Thorough examination of transport and magnetism in Cd 2 Os 2 O 7 has been recently reported by Mandrus et al. 8 with a Slater picture delivering a coherent interpretation of all experimental data. This particular mechanism in Cd 2 Os 2 O 7 may be favored by the fact that Os 5ϩ is in the 5d 3 configuration so that...

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confidence: 82%

Searching for the Slater transition in the pyrochloreCd2Os2O7<

2002

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“…Unlike most relaxors CNO does not contain any chemical disorder. However, among many phase transitions the one at about 196 K is characterized by a broad heat-capacity anomaly [103] and frequency-dependent change of dielectric constant [104]. While there is a controversy, whether the material should be classified as a relaxor [105], its dielectric properties must be related to the local dipole rearrangements.…”

Section: Pyrochloresmentioning

confidence: 98%

Diffuse scattering and local structure modeling in ferroelectrics

Paściak

Welberry²

2011

Zeitschrift für Kristallographie

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The excellent properties of modern ferroelectrics are the result of nanoscale local structure phenomena. Diffuse scattering, sensitive to the atomic correlations, is one of the few techniques that is able to provide detailed information on the local polar order. A review of diffuse scattering studies in ferroelectrics is given with special emphasis on those works where computer simulation techniques are used to analyse the experimental data. The examples comprise some well known materials, such as NaNO 2 or BaTiO 3 , but also modern ferroelectrics: lead-based relaxors, bismuth pyrochlores and BaTiO 3 related solid solutions.

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“…Unfortunately, up to now no measurements of this parameter were performed below room temperature. It is also known that a low-temperature transition to a monoclinic phase is typical for tungsten-bronze structures [17], with the appearance of a new polarization component, but the only experimental support of this transition for SBN-61 was published in Ref. [20].…”

Section: Discussionmentioning

confidence: 96%

“…2, together with the experimental THz points for the E||c polarization. It is possible to see that the permittivity due to the phonon contribution is low (ε ∼ 50) as in other tungsten-bronze materials [17], and that another excitation is present at and above room temperature below the phonon frequencies which contributes to THz values of ε and ε . On cooling this excitation gradually disappears.…”

Section: Ir and Thz Measurementsmentioning

confidence: 97%

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Broad-Band Dielectric Spectroscopy of Relaxor Ferroelectric Sr_0.61Ba_0.39Nb₂O₆

Buixaderas¹,

Kempa²,

Veljko³

et al. 2005

Ferroelectrics

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Broad-frequency range dielectric data of strontium barium niobate with 61% of Sr, from kHz to THz range, has been studied using various experimental techniques (FTIR, time-domain THz spectroscopy, HF coaxial technique and standard LF dielectric spectroscopy) in a wide interval of temperatures (20-600 K). Strong dielectric anisotropy was seen by all the experimental methods. Relaxor properties were detected in the ε * c response, where an intense relaxation slows down from the microwave range (T > T m ) and broadens to low frequencies on cooling. The slowing down stops below MHz near 200 K. On further cooling it disappears gradually from the spectra leaving a constant loss background. The high-frequency wing of this relaxation is seen also in the THz range at high temperatures. IR modes show standard behaviour with decreasing temperature and no anomalies in phonon frequencies were observed. This brings evidence for the order-disorder type of the ferroelectric phase transition. Dielectric data perpendicular to the polar axis show anomalous features at low temperatures, but there is no sufficient evidence for another phase transition suggested by other authors below 100 K.

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Phase transitions sequence in pyrochlore Cd2Nb2O7 studied by IR reflectivity

Cited by 45 publications

References 1 publication

Searching for the Slater transition in the pyrochloreCd2Os2O7<

Searching for the Slater transition in the pyrochloreCd2Os2O7<

Diffuse scattering and local structure modeling in ferroelectrics

Broad-Band Dielectric Spectroscopy of Relaxor Ferroelectric Sr_0.61Ba_0.39Nb₂O₆

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Phase transitions sequence in pyrochlore Cd2Nb2O7 studied by IR reflectivity

Cited by 45 publications

References 1 publication

Searching for the Slater transition in the pyrochloreCd2Os2O7<

Searching for the Slater transition in the pyrochloreCd2Os2O7<

Diffuse scattering and local structure modeling in ferroelectrics

Broad-Band Dielectric Spectroscopy of Relaxor Ferroelectric Sr0.61Ba0.39Nb2O6

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Product

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Broad-Band Dielectric Spectroscopy of Relaxor Ferroelectric Sr_0.61Ba_0.39Nb₂O₆