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Universal relaxor polarization in Pb(Mg1/3Nb2/3)O3 and related materials  [PDF]
A. A. Bokov,Z. -G. Ye
Physics , 2002, DOI: 10.1103/PhysRevB.66.064103
Abstract: The dielectric permittivity e at frequencies from [10^(-1) -10^(-5)] Hz to 10^5 Hz is studied in perovskite (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 relaxor ferroelectric ceramics of different compositions x = 0.35, 0.25 and 0, which exhibit, below the temperature of the diffuse epsilon'(T) maximum Tm, a tetragonal ferroelectric, a rhombohedral ferroelectric and a nonergodic relaxor phase, respectively. The universal relaxor dispersion previously observed at temperatures near and above Tm in the ceramics of x=0.25, is also found to exist in other compositions. This dispersion is described by the fractional power dependence of the real and imaginary parts of susceptibility on frequency. The real part of the universal relaxor susceptibility chi'U is only a comparatively small fraction of the total permittivity epsilon', but chi"U is the dominant contribution to the losses in a wide frequency-temperature range above Tm. In the high-temperature phase a quadratic divergent temperature behavior is observed for all the three compositions studied. The universal relaxor susceptibility is attributed to the polarization of polar nanoregions, which are inherent in the relaxor ferroelectrics. A microscopic model of this polarization is proposed, according to which the dipole moments of some ('free') unit cells inside polar nanoregion can freely choose several different directions, while the direction of the total moment of the nanoregion remains the same. The ensemble of interacting polar nanoregions is described in terms of a standard spherical model, which predicts the quadratic divergence of susceptibility above the critical temperature, in agreement with the experimental results.
Relaxation and freezing of dielectric response in relaxor Pb(Mg1/3Nb2/3)O3 crystal  [PDF]
A. A. Bokov,Z. -G. Ye
Physics , 2005, DOI: 10.1103/PhysRevB.74.132102
Abstract: Dielectric investigations of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 crystal were performed in the frequency domain at 10^(-4) 10^5 Hz. In the ergodic relaxor phase two overlapping relaxation processes obeying the Kohlrausch-Williams-Watts law, exp[-(t/tau)^beta], and the Curievon Schweidler law, t^(-n), respectively, were found and parameterized. The values of beta, n and 1/tau tend to zero at 211 K following the Vogel-Fulcher law, pointing to the glassy freezing of the dipole dynamics related to both relaxation processes.
Pb(Mg1/3Nb2/3)O3 (PMN) Relaxor: Dipole Glass or Nano-Domain Ferroelectric ?  [PDF]
Desheng Fu,Hiroki Taniguchi,Mitsuru Itoh,Shigeo Mori
Physics , 2013,
Abstract: Combining our comprehensive investigations of polarization evolution, soft-mode by Raman scattering and microstructure by TEM, and the results reported in the literatures, we show that prototypical relaxor Pb(Mg1/3Nb2/3)O3 (PMN) is essentially ferroelectric for T
Direct Observation and Quantitative Analysis of Anti-ferroelectric Fluctuations in Pb(Mg1/3Nb2/3)O3 Relaxor  [PDF]
A. Tkachuk,Haydn Chen
Physics , 2003,
Abstract: Synchrotron x-ray scattering studies of anti-ferroelectric nanoregions (AFR) as fluctuations, which give rise to 1/2(hk0) superlattice reflections (alpha spots), were systematically performed in Pb(Mg1/3Nb2/3)O3 (PMN) ferroelectric relaxor. Separation of the alpha spots from underlying diffuse scattering background allowed studying them as separate entities for the first time. AFR fluctuations were shown to be different from the chemical nanodomains (CND) and ferroelectric polar nano-regions (PNR). Instead, they are formed by anti-parallel short-range correlated Pb^2+ displacements that lead to unit cell doubling in <110> directions, based upon structure factor calculations. Correlation length is only on the 30 Ang scale, which defines the effective average size of the AFR fluctuations. This size remains temperature independent while the total number of AFRs significantly increases near the Vogel-Fulcher freezing temperature of 220 K. Presence of local fluctuations produced by anti-parallel atomic displacements can explain relaxor behavior as a result of competition between ferroelectric and anti-ferroelectrics type polar ordering in the glass-like systems.
Ferroelectric Ordering in the Relaxor Pb(Mg1/3Nb2/3)O3 as Evidenced by Low-Temperature Phonon Anomalies  [PDF]
S. Wakimoto,C. Stock,R. J. Birgeneau,Z. -G. Ye,W. Chen,W. J. L. Buyers,P. M. Gehring,G. Shirane
Physics , 2001, DOI: 10.1103/PhysRevB.65.172105
Abstract: Neutron scattering measurements of the lowest-energy TO phonons in the relaxor Pb(Mg1/3Nb2/3)O3 (PMN) are reported for 10<=T<=750 K. The soft mode, which is overdamped by the polar nanoregions below the Burns temperature T_d = 620 K, surprisingly recovers below 220 K. The square of the soft mode energy hw0^2 increases linearly with decreasing temperature, and is consistent with the behavior of a ferroelectric soft mode. At 10 K, hw0 reaches 11 meV, the same value observed in ferroelectric Pb(Zn1/3Nb2/3)O3 at low-T. An unusual broadening of the TA phonon starts at T_d and disappears at 220 K, coincident with the recovery of the TO mode. These dynamics suggest that a well-developed ferroelectric state is established below 220 K.
Mode-coupling and polar nanoregions in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3  [PDF]
S. Wakimoto,C. Stock,Z. -G. Ye,W. Chen,P. M. Gehring,G. Shirane
Physics , 2002, DOI: 10.1103/PhysRevB.66.224102
Abstract: We present a quantitative analysis of the phonon lineshapes obtained by neutron inelastic scattering methods in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN). Differences in the shapes and apparent positions of the transverse acoustic (TA) and transverse optic (TO) phonon peaks measured in the (300) and (200) Brillouin zones at 690 K are well described by a simple model that couples the TA and soft TO modes in which the primary parameter is the wave vector and temperature-dependent TO linewidth Gamma(q,T). This mode-coupling picture provides a natural explanation for the uniform displacements of the polar nanoregions, discovered by Hirota et al., as the PNR result from the condensation of a soft TO mode that also contains a large acoustic component.
Anelastic relaxor behavior of Pb(Mg1/3Nb2/3)O3  [PDF]
Hana Ursic,Dragan Damjanovic
Physics , 2013, DOI: 10.1063/1.4818665
Abstract: Elastic storage modulus and loss of relaxor lead magnesium niobate ceramics, Pb(Mg1/3Nb2/3)O3, have been measured with dynamic mechanical analyzer in single cantilever mode in the temperature range from 170 K to 320 K and at frequencies from 0.1 Hz to 50 Hz. The dependence of the elastic susceptibility (inverse modulus) on temperature and frequency of the driving force has characteristics of typical relaxor behavior that can be well described with the Vogel-Fulcher law. The parameters of the Vogel-Fulcher relation exhibit similar values for the dielectric and anelastic relaxations. Similarities and differences between anelastic and dielectric relaxor behaviors are identified.
Development of Ferroelectric Order in Relaxor (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3  [PDF]
Z. -G. Ye,Y. Bing,J. Gao,A. A. Bokov,P. Stephens,B. Noheda,G. Shirane
Physics , 2002, DOI: 10.1103/PhysRevB.67.104104
Abstract: The microstructure and phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain to be one of the most puzzling issues of solid state science. In the present work we have investigated the evolution of the phase symmetry in PMN-xPT ceramics as a function of temperature (20 K < T < 500 K) and composition (0 <= x <= 0.15) by means of high-resolution synchrotron x-ray diffraction. Structural analysis based on the experimental data reveals that the substitution of Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in the development of a clean rhombohedral phase at a PT-concentration as low as 5%. The results provide some new insight into the development of the ferroelectric order in PMN-PT, which has been discussed in light of the kinetics of polar nanoregions and the physical models of the relaxor ferroelectrics to illustrate the structural evolution from a relaxor to a ferroelectric state.
Soft Mode Anomalies in the Perovskite Relaxor Pb(Mg1/3Nb2/3)O3  [PDF]
P. M. Gehring,S. B. Vakhrushev,G. Shirane
Physics , 2000, DOI: 10.1063/1.1324469
Abstract: Neutron inelastic scattering measurements of the polar TO phonon mode in the cubic relaxor Pb(Mg1/3Nb2/3)O3, at room temperature, reveal anomalous behavior similar to that recently observed in the Pb(Zn1/3Nb2/3)_{0.92}Ti_{0.08}O3 system in which the optic branch appears to drop precipitously into the acoustic branch at a finite value of the momentum transfer q = 0.20 1/Angstroms, measured from the zone center. By contrast, a recent neutron study showed that PMN exhibits a normal TO phonon dispersion at 800 K. We speculate this behavior is common to all relaxor materials and is the result of the presence of nanometer-scale polarized domains in the crystal that form below a temperature Td, which effectively prevent the propagation of long wavelength (q = 0) phonons.
Relaxor behavior of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics
NingNing Wu,XueMei Song,YuDong Hou,ManKang Zhu,Chao Wang,Hui Yan
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0002-0
Abstract: In the present work, the phase transitions and relaxor behavior of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT, x = 0.2–0.4) ferroelectric ceramics have been investigated by means of X-ray diffraction, dielectric spectroscopy, the P-E hysteresis loop measurements and Raman scattering techniques. Structural analysis revealed that with the increase of PbTiO3 content, PMN-PT ceramics experienced a gradual phase transition process from rhombohedral to tetragonal. It is usually believed that such kinds of phase transitions resulted in the linear decrease of relaxation degree. Surprisingly, our analysis of the dielectric spectra revealed that the indicator of the degree of diffuseness y reached the maximum value near morphotropic phase boundary (MPB) (x = 0.32), then decreased with the further increase of PbTiO3 content. The large dielectric relaxor feature near MPB may be attributed to the formation of ordered nanodomains, resulting from complex coexisting nanostructures. Further, the P-E hysteresis loop measurements and Raman analysis of the B-site cation order correlated well with the dielectric measurement results. It was found that the hysteresis loop squareness R sq received the minimum value while the inverse of the value of full wide of half maximum (FWHM) of A1g mode reached the maximum value at MPB composition, which showed similar trends to y.
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