**3. Dielectric tunability properties of PVDF-based polymer**

The dielectric tunability of the PVDF has been studied by Lu et al. in 2008; the huge tunability can be reached in the P(VDF-TrFE) copolymer films, but in the P(VDF-TrFE-CFE) relaxor terpolymer films, the tunability is lower than the copolymer's [10]. For the traditional way of the relaxor ferroelectrics, the electric tunabilities are very large. Since the film thickness is controlled on a molecule level, ferroelectric LB polymer films have shown some exceptional properties, such as excellent crystallinity, two-dimensional ferroelectricity, surprising giant breakdown voltage, etc.; it is expected that terpolymer films derived from the LB technology can provide a special microstructure to study the origin of the excellent properties of relaxor ferroelectric terpolymers. High-quality ultrathin films of both ferroelectric P(VDF-TrFE) and relaxor ferroelectric P(VDF-TrFE-CFE) have been successfully fabricated by using the LB technique.

The P(VDF-TrFE-CFE) shows a typical relaxor from temperature dependences of the dielectric constant and dielectric loss versus frequency, as it is shown in Fig. 3.

**Figure 3.** The dielectric constant and dielectric loss of P(VDF-TrFE-CFE) LB films as a function of temperature. The inset is the peak temperature of dielectric constant Tm as a function of ln(*f*) and the parameters fitted with the Vogel– Fulcher relation

A tunability of 80 % at 240 MV/m was obtained in P(VDF-TrFE-CFE) terpolymer LB films (shown in Fig. 4), which is due to the highly ordered molecules and the high breakdown electric filed.

can be used for preparing the transducers, ferroelectric memory, gate of transistor, and uncooled infrared sensor. In the following paragraph, some special properties and applications

The dielectric tunability of the PVDF has been studied by Lu et al. in 2008; the huge tunability can be reached in the P(VDF-TrFE) copolymer films, but in the P(VDF-TrFE-CFE) relaxor terpolymer films, the tunability is lower than the copolymer's [10]. For the traditional way of the relaxor ferroelectrics, the electric tunabilities are very large. Since the film thickness is controlled on a molecule level, ferroelectric LB polymer films have shown some exceptional properties, such as excellent crystallinity, two-dimensional ferroelectricity, surprising giant breakdown voltage, etc.; it is expected that terpolymer films derived from the LB technology can provide a special microstructure to study the origin of the excellent properties of relaxor ferroelectric terpolymers. High-quality ultrathin films of both ferroelectric P(VDF-TrFE) and relaxor ferroelectric P(VDF-TrFE-CFE) have been successfully fabricated by using the LB

The P(VDF-TrFE-CFE) shows a typical relaxor from temperature dependences of the dielectric

**Figure 3.** The dielectric constant and dielectric loss of P(VDF-TrFE-CFE) LB films as a function of temperature. The inset is the peak temperature of dielectric constant Tm as a function of ln(*f*) and the parameters fitted with the Vogel–

**3. Dielectric tunability properties of PVDF-based polymer**

constant and dielectric loss versus frequency, as it is shown in Fig. 3.

will be introduced.

154 Ferroelectric Materials – Synthesis and Characterization

technique.

Fulcher relation

**Figure 4.** The tunability as a function of temperature for P(VDF-TrFE-CFE) LB films measured at 1 kHz, under the dc electric fields of 50, 100, 150, and 250 MV/m, respectively

What are the reasons for the large tunability in our terpolymer LB films? In our opinion, they should be associated with the special microstructure of the terpolymer LB films. It is known to us that LB polymers demonstrate some exceptional features such as good crystallinity and highly planar ordered and close parallel packing of the molecules.
