Coexistence of morphotropic phases in (1-x)Pb(Mg_1/3Nb _2/3)O₃-xPbTiO₃ solid solutions

We report the results of crystallographic analysis of various complex heterophase states that occur around the morphotropic phase boundary in the relaxor-based (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO ₃ solid solutions at room temperature. Different variants of the coexistence of two or three morphotropic phases are analyzed based on the structural data of Noheda et al. [Phys. Rev. B 66, 054104 (2002)] and Singh and Pandey [Phys. Rev. B 67, 064102 (2003)], and interpreted by taking into account the features of elastic matching of polydomain (twinned) regions. A model of interpenetrating phases is proposed to describe the two-phase states on the condition of a complete relieving of the mechanical stress at interfaces. A good agreement between the experimental and theoretical results on the variants of phase coexistence has been achieved.