Intermediate states in Pb(BI1/3II2/3)O3–PbTiO3 ferroelectric single crystals

Abstract Optical and dielectric studies of oriented and poled single crystal compositions on both sides of the morphotropic phase boundary in (1− x)Pb(Zn1/3Nb2/3)O3–xPbT iO3 have revealed an intermediate, metastable, ferroelectric orthorhombic state (FO) in a narrow composition range between the ferroelectric rhombohedral (FR) and tetragonal (FT) phases, which has also been identified from pyroelectric and dielectric data. Recently published structural data confirm this orthorhombic state for 0·08 < x < 0·11. Similarly, dielectric studies and electromechanical measurements on rhombohedral Pb(Mg1/3Nb2/3)O3–PbT iO3 single crystals have revealed an intermediate, metastable FO state at high temperature. Structural evidence of the orthorhombic phase in this system has also recently been reported. In the present paper it is shown that a metastable orthorhombic state is always close to but unstable with respect to the FR–FT degenerate states (morphotropy), as predicted by a phenomenological model for A(BI1− xBIIx)O3 ferroelectrics. Conditions for stabilising the nearly degenerate FR, FT and FO states in the Pb(BI1/3BII2/3)O3–PbT iO3 single crystal system are discussed in terms of the energy function tensor coefficients.