The phase transition between the ferroelectric and relaxor states for $0.8\mathrm{Pb}\left({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}\right){\mathrm{O}}_3\text{−}0.2\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_3$ 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 nonergodic 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 $344\mathrm{K}$: the transition temperatures on cooling and heating.

• Received 11 July 2006

DOI:https://doi.org/10.1103/PhysRevB.74.184106