Linear and Nonlinear Dielectric Response of VDF₆₀/Tr₄₀ Copolymer in the Vicinity of Ferroelectric Phase Transition

The effect of the bias electric field E₌ (0–10 kV/cm) on the dielectric properties of the VDF₆₀/Tr₄₀ copolymer was studied in the temperature range of 20–110°C. It was found that the dielectric nonlinearity Δε is negative in the polar phase and becomes positive above the Curie temperature (T_C). The increase in T_C under the field E₌ is not uniform. At E₌ < E_c (E_c is the threshold field), the Curie temperature is practically independent of E₌. At E₌ > E_c, an increase in T_C is observed. The presence of the threshold field indicates the existence of sources of random electric fields in the material under study. It is suggested that they are responsible for the smearing of the ferroelectric phase transition.