Study of slow lattice dynamics in relaxor ferroelectric PMN-30%PT by neutron spin echo technique

Slow lattice dynamics in the relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 were investigated by neutron spin echo technique. At much higher temperature than TC (400 K), we observed oscillating normalized intermediate scattering functions I(Q,t)/I(Q,0) for the [1-10] direction, which is ascribed to low frequency vibrational mode with ω - 40 μeV. Such low frequency mode suggests that flat energy surfaces exist in the free energy potential along the [1-10] direction, which could be associated with degeneracy between the rhombohedral and tetragonal ground states at morphotropic phase boundary. On cooling towards TC, the oscillation in I(Q,t)/I(Q,0) decreases and I(Q,t)/I(Q,0) becomes time-independent below TC. This indicates that the low frequency vibrational mode change into the slow relaxational mode showing giant responses. (author)