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 o r equal to x less than or equal to 0.40 were studied using impedance m easurements and high resolution x-ray powder diffraction. The dependen ce of the real and imaginary parts of the dielectric constant with tem perature was investigated on unpoled and poled ceramics, showing sever al transition points. The temperature dependence of the unit-cell para meters showed the onset of two successive spontaneous phase transition s: cubic-->tetragonal-->rhombohedral, A coexistence of both ferroelect ric 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 diele ctric informations. (C) 1996 American Institute of Physics.