Phase coexistence in [111] electric-field-cooled 0.7Pb(Mg1/3Nb2/3) O3-0.3PbTiO3 crystals

Features of phase coexistence in polydomain 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) crystals cooled under an applied [111] electric field E have been investigated. A sequence of ferroelectric phases as well as the elastic matching between coexisting phases in heterophase states has been analysed for cases where the angle between the spontaneous polarization vector of each domain type and the applied E vector remains equal in each ferroelectric phase. This analysis is based on a method that involves distortion matrices of the polydomain phases and invariants of interfaces regarded as quadric surfaces separating the phases. Results are represented in a system of diagrams linking domain states and interfaces at first-order phase transitions observed in [111] field-cooled 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) crystals. A 'fine' structure of the domain state -interface diagrams related to tetragonal-orthorhombic phase coexistence has been revealed. It has been shown that conditions for complete stress relaxation in different heterophase states are achieved for a phase sequence of cubic. polydomain tetragonal. near single-domain orthorhombic. single-domain monoclinic of the B type.