Critical point in ferroelectric Langmuir-Blodgett polymer films

Abstract

The ferroelectric critical point has been found in a ferroelectric polymer by exploring the influence of the electric field on the paraelectric-ferroelectric phase transition. Dielectric and pyroelectric measurements on 30-monolayer-thick films of the crystalline copolymer poly(vinylidene fluoride-trifluoroethylene) grown by Langmuir-Blodgett deposition show a single hysteresis loop below the zero-field phase transition temperature ${T}_{c0}=80\ifmmode\pm\else\textpm\fi{}10\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ double hysteresis loops between ${T}_{c0},$ and the critical temperature ${T}_{\mathrm{cr}}=145\ifmmode\pm\else\textpm\fi{}5\mathrm{}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}\mathrm{C},$ and no hysteresis above ${T}_{\mathrm{cr}}$ where the critical electric field is ${E}_{\mathrm{cr}}{=0.93\ifmmode\pm\else\textpm\fi{}0.1\ifmmode\times\else\texttimes\fi{}10}^{9}\mathrm{}\mathrm{V}/\mathrm{m}.$