D-E hysteresis loop

Figure 16.20 D-E hysteresis loop of LiTaCL measured by applying 10 mHz triangular wave voltage.

Fig. 4.5-96a,b MHPOBC. D — E hysteresis loops obtained from switching-current measurements. D is the electric displacement. Sample ceU thickness = 3 jjim. (a) Double hysteresis loop at 2 Hz. (b) Single hysteresis loop at 100 Hz... 

D-E Hysteresis Loop and Inversion Current the electric displacement D or the polarization P of the crystal is determined by the total summation of electric dipole moments in a unit volume the lattice. Therefore the change in dipole orientation should reflect on the D (and P) explicitly. The time dependence of elect dipole rcorwtslioo is equivalent to dm time evolution of charges, i.e., the current L A clear D-f hysteresis... 

The copolymer shows a D-E hysteresis loop. The value of the ramanent polarization is quite large, le.. 200-7D0 mOin at 1QS C due to the dipole polarization. At higher temperatures, DC conduction ot took impurities would siqterinqxKc on the dipole orientation current. Therefore, we attempted to conduct measurements at low temperatures, and recorded a D-E hysteresis loop that has a remanent polarization of 30 mOm (Fig. 15) (34). This value of remanent polarization coincides with the integratioo of thermally depolarizatioo current, which may be attributed to the CN dipole orientation. 

Rgura 23 Cunenl-field curve exdtiding DC ooaduction current and D-E hysteresis loop of N-phenyiaied aromatic polyurca at 120. (From Ret 18.)... 

Figure 35 shows Ibc D-E hysteresis cbaracleristks of PU79 and poly (nonunethyleneurea) PU9 obtained from the current density-eieGtric field curve, whicb excludes the DC conduction current of the san les (19]. The value of remanent polarization (P,) is 200-440 mCfin at 90 which may Ik attributed to an apparent effect from ionic currents of impurities. The reproducibility of P, depends on the crystallinity and molecular orientatiao, but Ibc same D-E hysteresis loop can be obtained for more than 100 cydes... 

In linear dielectrics D is directly proportional to E, increasing and decreasing linearly with E. In ferroelectric polymers, such as PVDF and the VDF TrFE copolymers, the surface charge density increases with the field in a nonlinear manner, and exhibits hysteresis as the field is decreased, with a significant amount of surface charge remaining when the field is completely removed. Subsequent applications and reversals of the electric field produce the characteristic D-E hysteresis loops shown in Fig. 5.4. 

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