Transition between the ferroelectric and relaxor states in 0.8Pb(Mg_(1/3)Nb_(2/3))O_3-0.2PbTiO_3 ceramics

摘要

The phase transition between the ferroelectric and relaxor states for 0.8Pb(Mg_(1/3)Nb_(2/3))O_3-0.2PbTiO_3 ceramics with high chemical homogeneity has been studied by measurements of the dielectric and elastic properties as a function of temperature and of thermal expansion. The room temperature ferroelectric phase structure has been studied in ceramics and powdered samples by Rietveld analysis of x-ray diffraction patterns and by ferroelectric hysteresis loops. Results indicate that the material has well defined, different transition and freezing temperatures, such as the transition is between a monoclinic Cm ferroelectric phase and the noner-godic glass state. The transition presents thermal hysteresis, not only in the transition temperature, but in the kinetics. This indicates that a quite sharp slowing down occurs in the temperature interval between 334 and 344 K: the transition temperatures on cooling and heating.