Far-infrared and dielectric spectroscopy of relaxor ferroelectric (Pb1-xLax)(Zr0.4Ti0.6)O3

The dielectric behavior of tetragonal (Pb1-xLax)(Zr0.4Ti0.6)O-3 (PLZT x/40/60) ceramics doped with lanthanum (x=12% and 15%) has been investigated from 10(2) to 10(14) Hz in the temperature range of 20-800 K. Relaxor ferroelectric behavior, together with a first-order ferroelectric phase transition at T-C below the dielectric maximum, was revealed. The lowest-frequency phonon partially softens to T-C and splits into two components in the ferroelectric phase. It is shown that similar splitting is typical for all relaxors even for samples without ferroelectric phase transitions, because the TO1 splitting occurs due to a local distortion in the polar clusters. A relaxational mode, assigned to the dynamics of polar clusters, was revealed in the teraherz spectra below 800 K. This mode slows down to the microwave range on cooling and finally anomalously broadens below T-C, which appears to be characteristic for all relaxors. In comparison to the rhombohedral (Pb1-xLa0.095)(Zr0.65Ti0.35)O-3, the low-temperature permittivity and dielectric losses are lower in the tetragonal PLZT as expected from the presence of the ferroelectric phase transition. (c) 2007 American Institute of Physics.