Central-Peak Components and Polar Soft Mode in Relaxor PbMg1/3Nb2/3O3Crystals

Bovtun, V.; Kamba, S.; Pashkin, Alexej; Savinov, M.; Samoukhina, P.; Petzelt, J.; Bykov, I. P.; Glinchuk, M. D.

doi:10.1080/00150190490423057

Cited by 94 publications

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“…5 At lower temperatures the loss maximum becomes so broad that only frequency independent dielectric losses can be seen. It can be fitted by a uniform distribution of relaxation frequencies, much broader than the experimental frequency window.…”

Section: Resultsmentioning

confidence: 99%

“…37 We suggest that this is due to the influence of random fields on the distribution of activation energies for breathing of polar clusters. 5 We measured also the in-plane dielectric response of PMN thin film on sapphire between 10 kHz and 1 MHz. Comparison of dielectric data obtained on single crystal and thin film is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…also investigated PMN single crystal by means of FTIR reflection spectroscopy and observed an underdamped TO1 SM at all temperatures below 300 K which obeyed the Cochran law. 5,31 Unfortunately they were not able to evaluate unambiguously FTIR data above room temperature, because the reflection band from the TO1 mode overlaps with that of the central mode (CM). Therefore we have decided to perform more sensitive FTIR transmission measurements on a thin PMN film.…”

Section: Introductionmentioning

confidence: 99%

“…The dielectric anomaly is not accompanied by any phase transition to polar state, and the structure remains cubic down to liquid He temperatures. 4 Nowadays it is generally accepted that the strong dielectric dispersion, which occurs in RFE in the broad spectral range from GHz to milliherz range 5,6 at temperatures around and below that of ε ′ (T) maximum T max , is a consequence of the dynamics of polar nano-clusters, which appear several hundred degrees above T max , at so called Burns temperature T d . 7 Although many papers have been devoted to RFE (see e.g.…”

Section: Introductionmentioning

confidence: 99%

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Soft and central mode behaviour in PbMg_1/3Nb_2/3O₃relaxor ferroelectric

Kamba¹,

Kempa²,

Bovtun³

et al. 2005

J. Phys.: Condens. Matter

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The relaxor ferroelectric PbMg 1/3 Nb 2/3 O3 was investigated by means of broad-band dielectric and Fourier Transform Infrared (FTIR) transmission spectroscopy in the frequency range from 1 MHz to 15 THz at temperatures between 20 and 900 K using PMN films on infrared transparent sapphire substrates. While thin film relaxors display reduced dielectric permittivity at low frequencies, their high frequency intrinsic or lattice response is shown to be the same as single crystal/ceramic specemins. It was observed that in contrast to the results of inelastic neutron scattering, the optic soft mode was underdamped at all temperatures. On heating, the TO1 soft phonon followed the Cochran law with an extrapolated critical temperature equal to the Burns temperature of 670 K and softened down to 50 cm −1 . Above 450 K the soft mode frequency leveled off and slightly increased above the Burns temperature. A central mode, describing the dynamics of polar nanoclusters appeared below the Burns temperature at frequencies near the optic soft mode and dramatically slowed down below 1 MHz on cooling below room temperature. It broadened on cooling, giving rise to frequency independent losses in microwave and lower frequency range below the freezing temperature of 200 K. In addition, a new heavily damped mode appeared in the FTIR spectra below the soft mode frequency at room temperature and below. The origin of this mode as well as the discrepancy between the soft mode damping in neutron and infrared spectra is discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Soft and central mode behaviour in PbMg_1/3Nb_2/3O₃relaxor ferroelectric

Kamba¹,

Kempa²,

Bovtun³

et al. 2005

J. Phys.: Condens. Matter

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“…In PMN, the frequency of the A 1 (TO1) mode increases on temperature lowering and it is obvious that this mode coincides with that which was denoted soft mode in the previous low temperature IR 11,14,15 and neutron studies. 20 On the contrary, the E 1 -component of TO1 mode seems to remain rather soft in all perovskite relaxors.…”

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confidence: 84%

Anisotropic Dielectric Function in Polar Nanoregions of Relaxor Ferroelectrics

et al. 2006

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The paper suggests to treat the infrared reflectivity spectra of single crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally frozen polarization makes the dielectric function strongly anisotropic in the phonon frequency range and the random orientation of the polarization at nanoscopic scale requires to take into account the inhomogeneous depolarization field. Employing a simple effective medium approximation (Bruggeman symmetrical formula) to dielectric function describing the polar optic modes as damped harmonic oscillators turns out to be sufficient for reproducing all principal features of room temperature reflectivity of PMN. One of the reflectivity bands is identified as a geometrical resonance entirely related to the nanoscale polarization inhomogeneity. The approach provides a general guide for systematic determination of the polar mode frequencies split by the inhomogeneous polarization at nanometer scale. In recent years, there has been enormous effort in studying single crystals with intrinsic nanoscopic inhomogeneity, since such materials often show a very interesting properties. It was even proposed that the clustered, inhomogeneous states encountered for example in high-Tc cuprates, CMR manganites, nickelates, cobaltites, diluted magnetic semiconductors or ferrolectric relaxors, should be considered as a new paradigm in condensed matter physics. 1 In case of relaxors, the peculiar dielectric properties of relaxor materials were associated with the presence of small polar clusters -so called polar nano-regions (PNR's)-already in the pioneer work of Burns and Dacol 2 . However, because of their small size and random nature, we still lack a clear understanding of their size distribution, thickness and roughness of their boundaries, their connectivity, shape anisotropy, distribution of the associated dipolar moments, their fractal self-similarity, their dynamics, and so on. PNR's are often represented as small islands submerged in a nonpolar matrix, possibly appearing and disappearing again in time. On the other hand, the recent piezoelectric scanning microscopy investigations 3 of the surface of PbTiO 3 -doped relaxors rather invoke a picture of a fine, hierarchical and essentially static "nanodomain" structure. It strongly suggests that the common perovskite relaxors are actually quite densely filled by quasi-static polar nano-regions, and that the former picture with prevailing non-polar matrix can perhaps be appropriate only at high temperatures around the so called Burns temperature. 2,4

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