Phase transition and phonon characteristics of PbTiO3 single-crystal nanorods prepared in NaCl flux

By annealing PbTiO3 (PT) nanoparticles together with surfactants in NaCl flux, single-crystal PT nanorods were prepared with diameters of 60-80nm and lengths of several micrometers. The PT nanorods are in tetragonal phase and grow along the (100) direction. A first-order phase transition from tetragonal (a=3.922 angstrom and c=3.963 angstrom) to cubic (a =c =3.942 angstrom) has been detected at 440 degrees C. With the increasing temperatures from 25 degrees C to 440 degrees C, the Raman mode E(1TO) exhibits a soften behavior from 74cm(-1) to 50 cm(-1), whereas the mode B1+E keeps its frequency almost unchanged at 286 cm-1. It is also noticed that both frequency and damping constant of mode E(1TO) show rapid changing with temperature only when temperature beyond 380 degrees C, blow the temperature they change very gradually. To explain the particular properties of the PT nanorods, the formation mechanism and an enhanced size effect have been discussed.