Switching properties of first-order ferroelectric thin films

A Landau-Devonshire theory with Landau-Khalatnikov dynamic equation is used to investigate the polarization reversal of first-order ferroelectric thin films. Spatial variation of the order parameter P is considered near the surfaces of ferroelectric film, where the surfaces are characterized by an extrapolation length δ . The two surfaces of ferroelectric film have been assumed to be identical, and symmetric boundary conditions are introduced. To simulate switching properties by an applied step field, Euler-Lagrange equation is solved numerically. The hysteresis loops, time evolution of average polarization and switching current are plotted for a few temperature intervals. The appearance of double hysteresis loops for temperature above the superheating temperature t S H suggests that the first-order ferroelectrics can behave like antiferroelectrics. It is discovered that in two temperature intervals ( t S C < t < t C and t C < t < t S H ) double-peaked switching curve appears, which implies that switching take place in two stages; and it may be due to the coexistence of paraelectric and ferroelectric phase within these temperature intervals.