Since Valasek's discovery of the ferroelectric properties of Rochelle
salt nearly 60 years ago, ferroelectricity has been regarded as one of
the tradi- tional branches of dielectric physics. It has had important
applications in lattice dynamics, quantum electronics, and nonlinear
optics. The study of electron processes in ferroelectrics was begun with
VUL's investigations of the ferroelectric properties of barium titanate
[1.1]. In- trinsic and extrinsic optical absorption, band structure,
conductivity and photoconductivity, carrier mobility. and transport
mechanisms were examined in this compound, and in other perovskite
ferroelectric semiconductors. An important discovery was that of the
highly photosensitive photoconducting ferroelectrics of type AVBVICVIII
(e.g. SbSI) by MERZ et al. in 1962 [1.2,3]. A large number of
ferroelectric semiconductors (some photosensitive, some not) are now
known, including broad-band materials (e.g. lithium niobate, lithium
tantalate, barium and strontium niobate, and type-A B I compounds), BI
and narrow-band semiconductors (e.g. type_AIVB compounds). A series of
improper ferroelectric semiconductors and photosensitive ferroelastics
have been discovered, of which Sb 0 I is an example. s 7 Owing to the
uncertainty of their band structure, the difficulty in deter- mining the
nature of the levels, the complexity of alloying, and their gen- erally
low mobility values, ferroelectrics are rarely of interest regarded as
nonlinear semiconductors. The most fruitful approach has been the study
of the influence of electrons (especially nonequilibrium electrons) and
electron excitations on phase transitions and ferroelectric properties.
A large group of phenomena have recently been discovered and
investigated.
