Local Polarization Distribution and Edwards-Anderson Order Parameter of Relaxor Ferroelectrics

Abstract

The temperature dependence of the Edwards-Anderson order parameter q EA and the local polarization distribution function W ͑ p͒ have been determined in a PMN single crystal via 2D 93 Nb NMR. A glasslike freezing of reorientable polar clusters occurs in the temperature range of the diffuse relaxor transition, whereas the NMR spectra corresponding to pinned nanodomains do not change with temperature. The obtained form of W ͑ p͒ as well as the temperature dependence of q EA and the nonlinear dielectric susceptibility can be well described by a newly proposed spherical random bondrandom field model of relaxor ferroelectrics.

Development of ferroelectric order in relaxor(1−x)Pb(Mg1/3Ye1, Bing2, Gao3 et al. 2003Phys. Rev. B

“…This model is complementary to the so-called spherical random bond -random field (RBRF) model proposed to explain the NMR data and the non-linearity of the total dielectric susceptibility in relaxors. 3,6 From the structural point of view, the average symmetry of PMN, when probed by conventional xray or neutron diffraction techniques, appears to be cubic (Pm3m) down to very low temperature with no evidence of macroscopic structural phase transition taking place through or below the temperature of maximum permittivity (T max = 265 K, at 1 kHz). However, diffuse scattering on the diffraction patterns were observed below the so-called Burns temperature T d (or T B ) ≈ 600 K, indicating the presence of locally polar regions of rhombohedral R3m symmetry, the volume ratio of which (over the cubic matrix) increases upon cooling to reach about 25% at 5 K. [10][11][12][13] Such an evolution of local structure is in agreement with the deviations from linearity of the refractive index, 14 the lattice parameters, the thermal expansion and strain, 10,15 which result from the presence PNRs.…”

“…The mechanism of the relaxor ferroelectric behavior continues to be a fascinating puzzle. Experimental data from neutron scattering, 2 nuclear magnetic resonance (NMR) 3 and measurements of nonlinear dielectric susceptibility, 3,4 pointed to the existence of a nonergodic structural glassy state in relaxors below a certain temperature. It is usually believed 3,5,6 that reorientational polar species responsible for the glassy behavior are composed of the clusters of low-symmetry structure having a size of a few nanometers, which were observed in relaxors.…”

“…Experimental data from neutron scattering, 2 nuclear magnetic resonance (NMR) 3 and measurements of nonlinear dielectric susceptibility, 3,4 pointed to the existence of a nonergodic structural glassy state in relaxors below a certain temperature. It is usually believed 3,5,6 that reorientational polar species responsible for the glassy behavior are composed of the clusters of low-symmetry structure having a size of a few nanometers, which were observed in relaxors. Recently, by means of dielectric spectroscopy, Bokov and Ye [7][8][9] have discovered a universal relaxor dispersion in PMN and related materials with different degrees of ferroelectric ordering, and showed that it is an important common property of relaxor ferroelectrics.…”

“…The complex perovskite Pb(Mg 1/3 Nb 2/3 )O 3 [PMN] exhibits typical relaxor ferroelectric properties, 1 characterized by the frustration of local polarization due to composition and field inhomogeneities, which prevents long-range ferroelectric order from developing completely. The mechanism of the relaxor ferroelectric behavior continues to be a fascinating puzzle.…”

“…The substitution of Ti 4+ for the complex (Mg 1/3 Nb 2/3 ) 4+ ions in the solid solution system between relaxor PMN and ferroelectric PbTiO 3 [PT], (1-x)PMN-xPT [PMN-xPT], results in a macroscopic ferroelectric phase with a morphotropic phase boundary (MPB) initially located at x ≈ 0.33, [22][23][24] separating the rhombohedral (relaxor side of the solid solution) and tetragonal (ferroelectric side) phases. Single crystals of PMN-PT with composition near the MPB are technologically promising materials for electromechanical transducers thanks to their excellent piezoelectric performance.…”