Doping effects on dynamical physical properties of Ca_(0.6)Sr_(0.4)Bi_4Ti_4O_(15) ferroelectric ceramics with layered-perovskite structure

摘要

The change of electrical and lattice dynamical properties of ferroelectric Ca_(0.6)Sr_(0.4)Bi_4Ti_4O_(15) (CSBT) ceramics were studied by doping with 0.1 wt.% of CeO_2 and MnO_2. The loss tangent and the AC conductivity decreased markedly due to the reduction of charge carrier. The activation energy of doped-CSBT increased owing to the reduction of intrinsic defects in the crystal lattice. For doped and pure CSBT, the appearance of thermal hysteresis and the satisfaction of the Cure-Weiss law by the dielectric susceptibility data assigned the first order nature of a ferroelectric phase transition. Especially in ferroelectric phases, the soft optic phonon mode showed the significant softening towards T_1 (at T_1, the square of soft mode frequency ω_s~2→0) and ω_s~2 was approximately proportional to T_1-T, where T_1 is ～70℃ above T_C=672℃, demonstrated a first order displacive nature of a ferroelectric phase transition. The invariance of lattice dynamical feature indicated that the crystal lattice did not influence markedly by the doping ions.