Recently, a new orthorhombic phase has been discovered in the ferroelectric system (1 Ϫx)Pb(Zn 1/3 Nb 2/3)O 3-xPbTiO 3 (PZN-xPT) for xϭ9%, and for xϭ8% after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations 10%рxр15%. The orthorhombic phase was observed for xϭ10%, but, surprisingly, for xу11% only a tetragonal phase was found down to 20 K. The orthorhombic phase thus exists only in a narrow concentration range with near-vertical phase boundaries on both sides. This orthorhombic symmetry (M C type͒ is in contrast to the monoclinic M A-type symmetry recently identified at low temperatures in the Pb(Zr 1Ϫx Ti x)O 3 ͑PZT͒ system over a triangle-shaped region of the phase diagram in the range xϭ0.46-0.52. To further characterize this relaxor-type system, neutron inelastic scattering measurements have also been performed on a crystal of PZN-xPT with xϭ15%. The anomalous soft-phonon behavior ͑''waterfall'' effect͒ previously observed for x ϭ0% and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.

Diffuse scattering around the ͑110͒ reciprocal lattice point has been investigated by elastic neutron scattering in the paraelectric and relaxor phases of the disordered complex perovskite crystal Pb(Zn 1/3 Nb 2/3 )O 3 ͑PZN͒. The appearance of a diffuse intensity peak indicates the formation of polar nanoregions at temperature T*, approximately 40 K above T c ϭ413 K. The analysis of this diffuse scattering indicates that these regions are in the shape of ellipsoids, more extended in the ͗111͘ direction than in the ͗001͘ direction. The quantitative analysis provides an estimate of the correlation length , or size of the regions, and shows that ͗111͘ ϳ1.2 ͗001͘ , consistent with the primary or dominant displacement of Pb leading to the low-temperature rhombohedral phase. Both the appearance of the polar regions at T* and the structural transition at T c are marked by kinks in the ͗111͘ curve but not in the ͗001͘ one, also indicating that the primary changes take place in a ͗111͘ direction at both temperatures.Many of the relaxor ferroelectrics known today are leadbased compounds with perovskite structure. In addition to the characteristic frequency dispersion of their dielectric constant, several of them exhibit remarkable piezoelectric or electrostrictive properties that are finding important applications, e.g., as transducers and actuators. The Pb 2ϩ -containing relaxor perovskites such as Pb(R 1/3 Nb 2/3 )O 3 (RϭMg 2ϩ , Zn 2ϩ ) have a common ABO 3 cubic perovskite structure in which the B site can be occupied by 1 3 R 2ϩ and 2 3 Nb 5ϩ . Because of the different atomic radii and valences of the B-site cation, PMN and PZN exhibit short-range chemical ordering. 1,2 Over the years, these relaxors and their properties have been described in a variety of ways, most often in terms of the formation of polar micro-or nanoregions. 3,4 However, these models are primarily based on indirect experimental evidence for such regions and more direct evidence is necessary in order to elucidate the true origin of the relaxor behavior. For this purpose, neutron and x-ray techniques are most suitable, as they can provide evidence of local structural ordering. Obtaining such evidence is crucial if the formation of polar regions is indeed responsible for the relaxor behavior.PZN is a prototype relaxor ferroelectric. It exhibits a large dielectric dispersion and a broad dielectric maximum that depend on both frequency and temperature. Earlier studies also reported a structural phase transition from cubic to rhombohedral symmetry near 413 K, 5,6 which falls in the temperature region of the maximum of the dielectric peak. More recent studies only mention the coexistence of cubic and rhombohedral phases, with polar nanodomains growing into polar microdomains 7 and their volume fraction increasing with decreasing temperature. Strain appears to play an important role in the nanodomain-to-microdomain phase transition, which therefore resembles a martensitic phase transformation. 7 In the last few years, PZN has also been intensively investiga...

Neutron elastic diffuse scattering experiments performed on Pb(Zn 1/3 Nb 2/3 )O3 (PZN) and on its solid solution with PbTiO3(PT), known as PZN-xPT, with x=4.5% and 9% around many reflections show that diffuse scattering is observed around reflections with mixed indices in the transverse and diagonal directions only. From the width of the diffuse scattering peak a correlation length is extracted. In PZN, we have reported that the diffuse scattering is more extended in the transverse than in the diagonal directions 1 . In the present work, the results show that the addition of PT leads to a broadening of the diffuse scattering along the diagonal, relative to the transverse directions, 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 the transition than in pure PZN (> 40 K), due to stronger correlations between the polar regions. Neutron inelastic scattering measurements have also been performed on PZN-xPT. The results show the broadening of the transverse acoustic (TA) phonon mode at a small momentum transfer q upon cooling. We attribute this broadening to the appearance of the polar nanoregions.

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