Doping effects on dynamical physical properties of Ca _0.6Sr _0.4Bi ₄Ti ₄O ₁₅ ferroelectric ceramics with layered-perovskite structure

The change of electrical and lattice dynamical properties of ferroelectric Ca _0.6Sr _0.4Bi 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 w ² _s →0) and w ² _s was approximately proportional to T ₁-T, where T ₁ is ∼70°C above T _C0672°C, 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.