Grain size effect on ferroelectric phase transition in Pb1-xBaxTiO3 ceramics

Micro-Raman scattering measurements in the frequency range of 5-1000 cm(-1) as well as X-ray diffraction have been carried out on nanocrystalline Pb1-xBaxTiO3 system. A grain size and Ba ion-induced phase transition from the tetragonal ferroelectric phase of PbTiO3 to the cubic paraelectric phase of BaTiO3 is found to occur at x similar to 0.7 and it is associated with the "softening'' of the mode at 74 cm(-1) (x = O) which arises from a delicate balance between long-range Coulomb forces and short-range repulsion. A lowest frequency phonon mode at 10 cm(-1) is detected and its grain size, Ba composition and temperature dependence appears to be correlated with structures for ABO(3) oxides. The temperature dependence of Raman phonon modes for Pb0.6Ba0.4TiO3 with grain size of 60 nm reveals a temperature-induced soft mode phase transition occurring at 360K. (C) 1998 Elsevier Science Ltd. All rights reserved.