GRAIN-SIZE EFFECT ON FERROELECTRIC PHASE-TRANSITION IN PB1-XBAXTIO3 CERAMICS

Micro-Raman scattering measurements in the frequency range of 5-1000 c m(-1) as well as X-ray diffraction have been carried out on nanocrysta lline Pb1-xBaxTiO3 system. A grain size and Ba ion-induced phase trans ition from the tetragonal ferroelectric phase of PbTiO3 to the cubic p araelectric 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 for ces and short-range repulsion. A lowest frequency phonon mode at 10 cm (-1) is detected and its grain size, Ba composition and temperature de pendence appears to be correlated with structures for ABO(3) oxides. T he temperature dependence of Raman phonon modes for Pb0.6Ba0.4TiO3 wit h grain size of 60 nm reveals a temperature-induced soft mode phase tr ansition occurring at 360K. (C) 1998 Elsevier Science Ltd. All rights reserved.