Antiferroelectic materials of Pb(Yb$_{1/2}$Ta$_{1/2}$)O$_{3}$ ceramics and liquid crystal CS4001 are studied for comparison of their rexation behaviors near the respective phase transitions.
Raman spectra of Pb(Yb$_{1/2}$Ta$_{1/2}$)O$_3$ reveals a phase transition from paraelectric to antiferroelectric phase at 300℃, and a diffuse phase transtion from antiferroelectric to ferroelectric phase at about 150℃. Raman spectra of Pb(Yb$_{1/2}$Ta$_{1/2}$)O$_3$ depicts $A_{1g}$, $E_g$, and 2 $F_g$ modes in ferroelectric phase, where the $A_{1g}$ mode is observed to decrease in frequency with decreasing temperature. The frequency shift of ω from $ω_0$, the hard core Einstein-mode frequency, is found to show a big jump at 300℃ in a similar form as seen with inverse real part dielectric constant. The $F_g$ mode associated at the displacement of Pb ions split from one peak structure in high temperature phase to three peaks in low temperature phase. And the splitting between peaks is observed to be increasing in the temperature region from 200℃ (antiferroelectric) to 100℃ (ferroelectric phase).
Liquid crystal CS4001 appears in a stripped pattern in antiferroelectric phase because of the modulation of smectic layer, when electro-optic double hysteresis loop can be observed.
Switching current dependence on temeprature and external field can be analyzed to follow the relaxational characteristics. In antiferroelectric phase, two peaks, P1 and P2, are observed with P1 peak showing a strong dependence on the frequency and amplitude of external field but P2 peak with a weak dependence. P1 peak corresponds to the field-induced transition from antiferroelectric to ferroelectric but P2 peak a spontaneous relaxation from ferroelectric to antiferroelectric state.
The relaxation time, controlling the switching time, is found to be a function of R, an effective rate constant determined as a peak to peak amplitude multiplied by frequency of the applied field.
