Relaxor Behaviors in Ferroelectric-Antiferroelectric Mixed Crystals

Abstract

In order to search for relaxor ferroelectrics or relaxor antiferroelectrics in Pb-excluded substances, ferroelectric and antiferroelectric mixed crystals Rb1-x(NH4)xH2PO4 are investigated from the theoretical viewpoint of the precursor to glass state. Both boundary regions between ferroelectric (FE) and glassy (G) phases, and between antiferroelectric (AFE) and glassy (G) phases are examined and relaxor-like behaviors are found in the present theory on X-ray diffraction and on dielectric constants. The relaxor-like behavior as an embryo of the glass is proposed in the antiferroelectric-glass (AFE-G) phase boundary region where the growth of glass ordering is shown in quite a different pattern from that of the FE-G phase boundary region. The condition for appearance of the relaxor is discussed as being due to the proton spatial correlation in structurally frustrated systems.