RELAXOR FERROELECTRICS: AN OVERVIEW

The paper will trace the evolution of understanding related to the modification of sharp ferroelecmc phase transition behavior that occurs in composition systems which exhibit diffuse and relaxor ferroelectric properties. The focus will be primarily upon the perovskite structure families where cations of different valence occupying similar crystallographic sites in the structure appear to play an important role. Limited ordering in the Pb(B1B2)O-3 systems will be discussed and possible mechanisms for self limiting to nanometer scales in some systems explored. New studies of the break up of the simple ferroelectric behavior in lanthanum modified lead zirconate titanate (PLZT) and in lead titanate (PLT) systems will be discussed and the relevance to the general problem of relaxor behavior examined. Evidence for enhanced polarization fluctuations and super paraelectric behavior at high temperatures will be discussed and random field and spin glass models for the lower temperature state considered. In the tungsten bronze structure relaxors barium strontium niobate (SBN) and lead barium niobate (PBN) the behavior is more complex suggesting the possibility for relaxor behavior in directions orthogonal to existing polarization systems.