**6. Abnormal polarization switching of relaxor terpolymer films at low temperature**

The temperature dependences of the dielectric and ferroelectric properties of terpolymer films produced using the LB method were systematically investigated, with an emphasis on the nature of the ferroelectricity at low temperatures [18].

The change of remanent polarization (*Pr*) with temperature is not sharp, and a broad peak at around 265 K is seen for *∂Pr/∂T* (Fig. 8(a)).

A broad peak at ~270 K is displayed in the plot of *∂D/∂EE=0* versus T (Fig. 8(b)). The coercive field (*Ec*) increases slowly with decreasing temperature to ~265 K, below which it increases rapidly (Fig. 8(c)). This verifies that a ferroelectric phase transition occurs at ~270 K in the P(VDF-TrFE-CFE) films. The *Pr* value of the P(VDF-TrFE-CFE) film is smaller than that of the P(VDF-TrFE) film, and the magnitude of the *Pr* of the P(VDF-TrFE-CFE) film is still smaller than that of the film's saturation polarization (*Ps*) (Fig. 8(d)).

This suggests that some less-polar molecular conformations (TTTG') still affect the polarization switching. A deviation from Merz's law was observed in the relationship between the coercive

**Figure 8.** Temperature dependence of (a) *Pr* (left), *∂Pr/∂T* (right); (b) *Ec* (left), 1*∂D/∂EE=0* (right); and (c) *Ec* derived from *P-E* loop at zero *Pr* (left), *∂EC/∂T*(right). (d) *P-E* loops of P(VDF-TrFE-CFE) and P(VDF-TrFE) films at 210 K and 100 Hz

**Figure 9.** Relationship between 1/Ec and ln*f* for relaxor P(VDF-TrFE-CFE) terpolymer films

The ferroelectric-like phase transition is observed in the P(VDF-TrFE-CFE) terpolymer films as the thickness is lower than 3 nm. The ferroelectric-like features are considered to result from

**Figure 7.** The temperature dependence of *C*-*V* curve at 10 kHz for one transferred layer terpolymer film. (a) 300 K, (b)

**6. Abnormal polarization switching of relaxor terpolymer films at low**

The temperature dependences of the dielectric and ferroelectric properties of terpolymer films produced using the LB method were systematically investigated, with an emphasis on the

The change of remanent polarization (*Pr*) with temperature is not sharp, and a broad peak at

A broad peak at ~270 K is displayed in the plot of *∂D/∂EE=0* versus T (Fig. 8(b)). The coercive field (*Ec*) increases slowly with decreasing temperature to ~265 K, below which it increases rapidly (Fig. 8(c)). This verifies that a ferroelectric phase transition occurs at ~270 K in the P(VDF-TrFE-CFE) films. The *Pr* value of the P(VDF-TrFE-CFE) film is smaller than that of the P(VDF-TrFE) film, and the magnitude of the *Pr* of the P(VDF-TrFE-CFE) film is still smaller

This suggests that some less-polar molecular conformations (TTTG') still affect the polarization switching. A deviation from Merz's law was observed in the relationship between the coercive

the induced electric field due to the mirror charges in the electrodes.

nature of the ferroelectricity at low temperatures [18].

than that of the film's saturation polarization (*Ps*) (Fig. 8(d)).

around 265 K is seen for *∂Pr/∂T* (Fig. 8(a)).

**temperature**

340 K, (c) 360 K, and (d) 375 K

158 Ferroelectric Materials – Synthesis and Characterization

field and the frequency (Fig. 9). The deviation from Merz's law at high frequency further evidences the presence of *TTTG'* conformations in the ferroelectric state.

The relaxor P(VDF-TrFE-CFE) terpolymer, the CFE monomer is introduced into the ferroelec‐ tric P(VDF-TrFE) copolymer as a defect, leading to all-trans polar conformations being converted into less-polar conformations, i.e., *TTTG',* which are considered to be nanometersized all-trans conformations. The dynamics of the *TTTG'* conformations of P(VDF-TrFE-CFE) films under electric fields or on cooling demonstrate a behavior different from that of the polar nanoregions (PNRs) of the Pb(Mg1/3Nb2/3)O3 (PMN) system [19]. The weak intermolecular interactions impede the development of some *TTTG'* conformations into all-trans ones along the direction perpendicular to the molecular chains, so these *TTTG'* conformations can largely retain their dynamics. This may be responsible for both the relaxor nature of the P(VDF-TrFE-CFE) terpolymer and the difference between its *Pr* and *Ps* values, even in its ferroelectric state.

The temperature dependences of the ferroelectricity of P(VDF-TrFE-CFE) terpolymer films were systemically investigated. Both the polarization current (*∂*Pr/*∂*T) and the dielectric response derived from the *P-E* loop at zero field, suggesting that a ferroelectric phase transition occurs at 270 K. Distinct differences were observed in the P(VDF-TrFE-CFE) terpolymer films compared with perovskite relaxors, e.g., a broad peak in the *∂*Pr/*∂*T curve, deviation from Merz's law at high frequency, and a smaller activation field [20]. These differences are considered to be caused by the existence of the less-polar *TTTG* conformation in the ferroelec‐ tric state.
