Structural and dielectric studies of Pb(Mg1/3Nb2/3)O-3-PbTiO3 ferroelectric solid solutions around the morphotropic boundary

Solid solutions (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) with 0.20 less than or equal to x less than or equal to 0.40 were studied using impedance measurements and high resolution x-ray powder diffraction. The dependence of the real and imaginary parts of the dielectric constant with temperature was investigated on unpoled and poled ceramics, showing several transition points. The temperature dependence of the unit-cell parameters showed the onset of two successive spontaneous phase transitions: cubic-->tetragonal-->rhombohedral, A coexistence of both ferroelectric phases was evidenced in a large temperature and composition range, The dielectric and structural properties were interpreted in terms of relaxor-->ferroelectric spontaneous phase transition. An intermediate behavior between a relaxer and a real ferroelectric was evidenced. A partial phase diagram was proposed including both structural and dielectric informations. (C) 1996 American Institute of Physics.