We have investigated the whole phase diagram of ${\mathrm{PbSc}}_{1∕2}{\mathrm{Nb}}_{1∕2}{\mathrm{O}}_3-{\mathrm{PbTiO}}_3$ (PSN-PT) solid solution by Raman scattering and compared the results to our recent x-ray and theoretical study on this system [R. Haumont et al., Phys. Rev. B 71, 104106 (2005)]. Changes in the vibration bands associated to the sequence of phase transitions $R3m\text{−}Cm\text{−}Pm\text{−}P4mm$ by doping PSN with ${\mathrm{Ti}}^{4+}$ were evidenced, especially between the two monoclinic phases. The detailed analysis also pointed out that the monoclinic order probably already exists into the rhombohedral and the tetragonal phases on a local scale which makes the morphotropic phase region (MPR) more extended than it was reported. Moreover, besides the polar states this Raman analysis evidences the strong chemical inhomogeneities existing on a nanometer scale in such relaxor-based system such as the Ti-rich and $\mathrm{Sc}∕\mathrm{Nb}$-rich regions.

• Received 18 July 2005

DOI:https://doi.org/10.1103/PhysRevB.73.104106