Low frequency phonon modes and ferroelectric phase transitions in nanocrystalline Pb(1-x)A(x)Ti(1-y)B(y)O(3) system

Low frequency Micro-Raman scattering measurements as well as X-ray diffract ion have been carried out on nanocrystalline PbZr1-yTiyO3, Pb1-xSrxTiO3 Pb1 -xLaxTiO3 and Pb1-xBaxTiO3 system. Grain sizes-induced and different doping ions-induced phase transitions from the tetragonal ferroelectric phase to the cubic paraelectric phase were identified in these ABO(3) systems. These phase transitions are closely concerned with the "softening" of the low fr equency phonon modes. A lowest frequency phonon mode at 10cm(-1) is detecte d. The temperature dependence of Raman phonon modes for Pb0.8BLa0.2TiO3 Wit h grain size of 58 nm reveals a temperature-induced soft mode phase transit ion occurring at 375 K. The "softening" of the low frequency modes with red ucing grain size and increasing doping ion content and temperature is shown to arise from a delicate balance between long-range Coulomb forces and sho rt-range repulsion. Investigations show that PbTiO3 has an adjustable Curie temperature depending on different dopants and different grain sizes which will be useful in sensor and actuator devices.