Freezing of the local dynamics in the relaxor ferroelectric [Pb(Zn _1/3Nb _2/3)O ₃] _0.955[PbTiO ₃] _0.045

We report measurements of the neutron diffuse scattering in a single crystal of the relaxor ferroelectric material 95.5%Pb(Zn _1/3Nb _2/3)O ₃-4.5%PbTiO ₃ (PZN-4.5%PT). We show that the diffuse scattering at high temperatures has a quasielastic component with energy width 0.1 meV. On cooling the total diffuse scattering intensity increases, but the intensity and the energy width of the quasielastic component gradually diminish. At 50 K the diffuse scattering is completely static (i.e., the energy width lies within the limits of our instrumental resolution). This suggests that the dynamics of the short-range correlated atomic displacements associated with the diffuse scattering freeze at low temperature. We find that this depends on the wave vector q as the quasielastic diffuse scattering intensities associated with 001 (T1-type) and 110 (T2-type) atomic displacements vary differently with temperature and electric field.