Screening of Spontaneous Polarization

Abstract

In the first two chapters we discussed the role of the electron subsystem in the mechanism of ferroelectric phase transitions and the appearance of spontaneous polarization. A ferroelectric was regarded as an infinitely extended homogeneous crystal. For a real ferroelectric the boundary conditions must be determined, i.e. values of the polarization P (or displacement D) must be assigned on the surface. It is clear from energy considerations that on the surface of a ferroelectric the normal component of the spontaneous polarization must be zero; in other words, it must be screened. For ferroelectric semiconductors this screening must be internal, accomplished by electrons or holes. Nonequilibrium carriers in photoferroelectrics make an additional contribution to the screening.