RAMAN INVESTIGATION OF UNDOPED, NIOBIUM-DOPED, AND LANTHANUM-DOPED LEAD-ZIRCONATE-TITANATE CERAMICS

In a previous article, we proved and characterized a phase transition of an order-disorder type, below room temperature, in the Pb1-3X/2LaX square(X/2)(Zr0.95Ti0.05)O-3 (X=0.5-4 wt % La) ceramics. In the presen t article, the analysis of this order-disorder transition is continued on the basis of the comparative study of Raman scattering, as a funct ion of the Nb or La dopant. The parallel analysis and the interpretati on of the Raman spectra of the nondoped,,Nb-doped, and La-doped Pb(Zr0 .95Ti0.05)O-3 ceramics lead to new information concerning the identifi cation of the vibrational modes involved. In addition, the correlation between the phase transitions and the nature of the dopants is establ ished. New information concerning the cell doubling, during the ferroe lectric low temperature to ferroelectric high temperature phase transi tion, is obtained as well. The Raman study of the lead-lanthanum zirco nate-titanate ceramics allowed us to identify for the first time the s o-called ''antiferroelectric mode'' and ''ferroelectric mode'' which h ad been theoretically predicted. (C) 1995 American Institute of Physic s.