| Single-crystal solid solution of the relaxor ferroelectrics Pb(Zn 1/3Nb2/3)O3 and ferro-electric PbTiO3, known as PZN-xPT, is under active consideration for a new generation of electromechanical transducers. Particularly important are the compositions near the vertical phase boundary between rhombohedral and tetragonal, the so-called “morphotropic phase boundary”, where the remarkable piezoelectric and electrostrictive properties are enhanced. However, the fundamental origin of these properties remains a puzzle. The difficulties in understanding originate from the high complexity of these materials, characterized by chemical, compositional and orientational disorder that coexists with the presence of short-range order. The important characteristic feature of the relaxor ferroelectrics is attributable to the appearance of the polar nanoregions (PNRs) which are in the focus of this work.; Firstly, in order to characterize these regions, neutron elastic diffuse scattering study is addressed on the PZN- xPT crystals (x = 0, 4.5, and 9%). The appearance of a diffuse scattering peak indicates the formation of these regions. The analysis of this diffuse scattering indicates that, with increasing PT, the local polarization direction remains unchanged, but the PNRs preferentially grow in a different direction. Also, with the addition of PT, the PNRs condense at a higher temperature above the transition than in pure PZN.; Secondly, we present results from neutron inelastic scattering measurements of the PZN-xPT crystals. This study provides information on the condensation of the PNRs and on their slow dynamics, directly through the central peak and, indirectly, through their coupling to transverse acoustic phonons. Both elastic and inelastic studies allow identification of three important stages in the evolution of the PNRs with decreasing temperature. This behavior seems to be characteristic of all relaxor ferroelectrics.; Finally, by means of X-ray powder diffraction on the PZN-xPT crystals (10% ≤ x ≤ 15%), the full extent of a new lower symmetry phase is determined. As a result, the low symmetry phase with orthorhombic symmetry has been found to exist in a narrow composition region between rhombohedral and tetragonal phases (8% < x < 11%). A detailed structural analysis, together with study of Ref. [18, 60], have led us to establish a new phase diagram of PZN-xPT. |
