Infrared and Raman spectroscopy of [Pb(Zn(sub 1/3)Nb(sub 2/3))]O3](sub 0.92)-[PbTiO3](sub 0.08) and [Pb(Mg(sub 1/3)Nb(sub 2/3))O3](sub 0.71)-[PbTiO3](sub 0.29) single crystals

The lattice dynamics in all three crystal phases namely cubic, tetragonal and rhombohedral of [Pb(Mg(sub 1/3)Nb(sub 2/3))O3]-[PbTiO3] (PMN-PT) and [Pb(Zn(sub 1/3)Nb(sub 2/3))]O3]-[PbTiO3] (PZN-PT) single crystals are studied by means of infrared (IR) and Raman spectroscopies. IR and Raman spectroscopy confirm the locally doubled unit cell in the paraelectric and ferroelectric phases due to the ordering in the perovskite B sites and occurrence of polar nanoclusters in the paraelectric phase.