Soft Mode Anomalies in the Perovskite Relaxor Pb(Mg1/3Nb2/3)O3
arXiv:cond-mat/0002464 · 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.
5 pages, 4 figures To appear as an AIP Conference Proceedings Volume for the Aspen 2000 Winter Conference on the Fundamental Physics of Ferroelectrics