Relaxor behavior of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics

In the present work, the phase transitions and relaxor behavior of (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-PT, x = 0.2–0.4) ferroelectric ceramics have been investigated by means of X-ray diffraction, dielectric spectroscopy, the P-E hysteresis loop measurements and Raman scattering techniques. Structural analysis revealed that with the increase of PbTiO₃ content, PMN-PT ceramics experienced a gradual phase transition process from rhombohedral to tetragonal. It is usually believed that such kinds of phase transitions resulted in the linear decrease of relaxation degree. Surprisingly, our analysis of the dielectric spectra revealed that the indicator of the degree of diffuseness y reached the maximum value near morphotropic phase boundary (MPB) (x = 0.32), then decreased with the further increase of PbTiO₃ content. The large dielectric relaxor feature near MPB may be attributed to the formation of ordered nanodomains, resulting from complex coexisting nanostructures. Further, the P-E hysteresis loop measurements and Raman analysis of the B-site cation order correlated well with the dielectric measurement results. It was found that the hysteresis loop squareness R _sq received the minimum value while the inverse of the value of full wide of half maximum (FWHM) of A_1g mode reached the maximum value at MPB composition, which showed similar trends to y. Supported by the National Natural Science Foundation of China (Grant No. 60601020), Project of New Star of Science and Technology of Beijing (Grant No. 2007A014), Natural Science Foundation of Beijing (Grant No. 4072006), Science and Technology Development Project of Beijing Education Committee (Grant No. KM200810005012)