  A correlation between structure and vibrational properties related to a
ferroelectric to paraelectric phase transition in perovskite
Pb(1-x)(Na0.5Sm0.5)xTiO3 (PNST - x) polycrystalline powders is discussed.
Substitution leads to reduction of tetragonality which is associated with a
shift of the phase transition to lower temperatures. The nature of the phase
transition gets diffused with increasing substitution.
