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

Abstract

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≈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.