Diffuse neutron scattering study of relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT)

Diffuse neutron scattering is a valuable tool to obtain information about the size and orientation of the polar nanoregions that are a characteristic feature of relaxor ferroelectrics. In this paper, we present new diffuse scattering results obtained on Pb(Zn1/3Nb2/3)O3 (PZN for short) and (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) single crystals (with x=4.5 and 9%), around various Bragg reflections and along three symmetry directions in the [100]-[011] zone. Diffuse scattering is observed around reflections with mixed indices, (100), (011) and (300), and along transverse and diagonal directions only. No diffuse scattering is found in longitudinal scans. The diffuse scattering peaks can be fitted well with a Lorentzian function, from which a correlation length is extracted. The correlation length increases with decreasing temperatures down to the transition at Tc, first following a Curie-Weiss law, then departing from it and becoming flat at very low temperatures. These results are interpreted in terms of three temperature regions: 1) dynamic polarization fluctuations (i.e. with a finite lifetime) at high temperatures, 2) static polarization reorientations (condensation of polar nanoregions) that can still reorient as a unit (relaxor behavior) at intermediate temperatures and 3) orientational freezing of the polar nanoregions with random strain fields in pure PZN or a structural phase transition in PZN-xPT at low temperatures. The addition of PT leads to a broadening of the diffuse scattering along the diagonal ([111]) relative to the transverse ([100]) direction, indicating a change in the orientation of the polar regions. Also, with the addition of PT, the polar nanoregions condense at a higher temperature above Tc