Phase diagram of the relaxor ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3

Recently, a new orthorhombic phase has been discovered in the ferroelectric system (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-xPT) for x=9%, and for x=8% after the application of an electric field. In the present work, synchrotron x-ray measurements have been extended to higher concentrations 10%≤x≤15%. The orthorhombic phase was observed for x=10%, but, surprisingly, for x≥11% 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 (MC type) is in contrast to the monoclinic MA-type symmetry recently identified at low temperatures in the Pb(Zr1-xTix)O3 (PZT) system over a triangle-shaped region of the phase diagram in the range x=0.46–0.52. To further characterize this relaxor-type system, neutron inelastic scattering measurements have also been performed on a crystal of PZN-xPT with x=15%. The anomalous soft-phonon behavior (‘‘waterfall’’ effect) previously observed for x=0% and 8% is clearly observed for the 15% crystal, which indicates that the presence of polar nanoregions extends to large values of x.