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A phenomenological theory of dielectric and mechanical properties of improper ferroelectric crystals
Author(s) -
Kobayashi J.,
Enomoto Y.,
Sato Y.
Publication year - 1972
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220500139
Subject(s) - ferroelectricity , dielectric , condensed matter physics , materials science , polarization (electrochemistry) , phenomenological model , dielectric response , crystal (programming language) , microscopic theory , physics , chemistry , computer science , optoelectronics , programming language
A phenomenological theory has been developed for explaining the anomalous dielectric and electro‐mechanical properties of some improper ferroelectrics. An ordering parameter 8, which plays the role of a trigger for the onset of the spontaneous polarization P is introduced into the thermodynamical potential function. The peculiar dielectric properties of (NH 4 ) 2 SO 4 ‐ and Gd 2 (MoO 4 ) 3 ‐group crystals and the anomalous behaviour of the lattice strains of Fe‐I‐boracite can be well explained on the basis of this theory. A graphical investigation in a proper θ– P plane shows how the strength of the coupling between 8 and P characterizes the transition mechanisms of the improper ferroelectrics. As a result, it has become clear that the common origin of the peculiar physical properties of both crystal groups lies in the extreme weakness of the couplings. Experimental methods to disclose improper ferroelectric mechanisms are discussed.