Doping effects on dynamical physical properties of Ca0.6Sr0.4Bi4Ti4O15 ferroelectric ceramics with layered-perovskite structure

The change of electrical and lattice dynamical properties of ferroelectric Ca0.6Sr0.4Bi4Ti4O15 (CSBT) ceramics were studied by doping with 0.1 wt.% of CeO2 and MnO2. 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 $$ \omega_{\text{s}}^2 $$  → 0) and $$ \omega_{\text{s}}^2 $$ was approximately proportional to T 1-T, where T 1 is ~70°C above T C = 672°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.