Electron microscopy
 
Ferroelectric Dielectric Hysteresis & Hysteresis Loop
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Dielectric hysteresis was discovered by Valasek [1] and may be defined as an effect in a dielectric material similar to the hysteresis found in magnetic materials. In this case, the electric displacement D for one direction in the crystal (parallel to the x axis) was not only determined by the applied field E, but also depended on its previous values.

A typical hysteresis loop is shown in Figure 1804a. At low electric fields and at very high electric fields a ferroelectric behaves like an ordinary dielectric with a high dielectric constant, but at the coercive field Ec polarization reversal occurs and induces a large dielectric non-linearity. At zero field (E0) the electric displacement within a single domain has two values (-Pr and +Pr), representing the opposite orientations of the spontaneous polarization. In a multiple-domain crystal the average zero-field displacement can have any value between these two extremes (-Pr < D < +Pr).

typical dielectric hysteresis loop

Figure 1804a. A typical dielectric hysteresis loop (Ec: coercive field; Ps: spontaneous polarization; and Pr: remanent polarization).

Different from ferroelectric hysteresis, the schematic illustrations in Figure 1804b show D-E loops of four non-ferroelectric dielectrics.

 
Lossless
Lossy
Linear
Linear lossless dielectric
(a)
Linear lossy dielectric
(b)
Non-linear
Non-linear lossless dielectric
(c)
Non-linear lossy dielectric
(d)

Figure 1804b. D-E loops of four non-ferroelectric dielectrics: (a) Linear lossless dielectric, (b) Linear lossy dielectric, (c) Non-linear lossless dielectric, and (d) Non-linear lossy dielectric.

 

 

 

 

 

[1] Valasek, J. (1921). Piezo-electric and allied phenomena in rochelle salt. Phys. Rev., 17, 475.

 

 

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