PHONON CHARACTERISTICS OF THIN-FILM AND NANOPHASE LEAD TITANATE

Phonon natures in ferroelectric lead titanate (PT) thin films and ultr afine grains are examined by Raman spectroscopy. All phonons are compa red with those in the bulk crystals. Two kinds of phonons were recorde d in the thin films to show downward and upward frequency shift, attri buted to tensile and compressive stress arisen from, the silicon subst rate, respectively A new soft mode A(1)(TO) at 104 cm(-1) is observed in the films for the first time, which satisfies Curie-Weiss relation, manifesting the mean field slowing-down effect. The downward frequenc y-shift in nanocrystalline PT is to be ascribed to surface tension eff ect, rather than residual stress in grain boundaries.