CRITICAL-POINT IN FERROELECTRIC LANGMUIR-BLODGETT POLYMER-FILMS

The ferroelectric critical point has been found in a ferroelectric pol ymer by exploring the influence of the electric field on the paraelect ric-ferroelectric phase transition. Dielectric and pyroelectric measur ements on 30-monolayer-thick films of the crystalline copolymer poly(v inylidene fluoride-trifluoroethylene) grown by Langmuir-Blodgett depos ition show a single hysteresis loop below the zero-field phase transit ion temperature T-c0 = 80 +/- 10 degrees C, double hysteresis loops be tween T-c0, and the critical temperature T-cr = 145 +/- 5 degrees C, a nd no hysteresis above T-cr where the critical electric field is E-cr = 0.93+/-0.1x10(9) V/m.