Raman scattering investigation of the phase transition in nanocrystalline (Pb, Ca, La)TiO3

Nanocrystalline (Pb0.95-xCa0.05Lax)Ti1-x/4O3 (PCLT) powders were prepared by the sol-gel technique. Doping-induced or grain size-induced structure phase transition was investigated by using Raman scattering and x-ray diffraction for the PCLT system. Experimental results show that the soft phonon mode E(TO1) displays a decrease in frequency but an increase in linewidth with increasing concentration of La. A discontinuous behavior of the phonon energy is associated with a phase transition from a ferroelectric tetragonal to a paraelectric cubic phase, and occurs at a morphotropic phase boundary of x approximate to 0.30 for grain sizes being 20 nm. The dependence of Raman phonon modes on the size of particles has been analyzed for nanocrystalline (Pb0.88Ca0.04La0.08)Ti0.98O3 with grain sizes of 10-60 nm and a grain size-induced phase transition is observed for sizes below 14 nm. (C) 1999 American Institute of Physics. [S0021-8979(99)01221-9].