On the Phenomenon of Morphotropic Tetragonal-Rhombohedral Phase Boundary in the Ferroelectric Ceramics

The structural and dielectric properties have been studied on 0.1 Pb_0.9K_0.1(Zn_1⁄3Nb_2⁄3)O_2.95–xPbZrO₃–(0.9–x)PbTio₃ solid solutions in the region of morphotropic phase boundary between tetragonal and rhombohedral structures. In the X-ray analysis, the{200} reflections which were mainly selected to investigate are split into three lines, in which two are due to the tetragonal structure and central one is due to the rhombohedral structure in the miscibility gap between x=0.43∼0.55. The phase boundary between two structures is not a line but a region, where the lattice parameters of each phase remain constant. In the dielectric study, the appearance of two phases is also investigated, being based on the “mixing rule” from the volume fractions and the dielectric constants of two phases. The Curie temperature of each phase does not change in the coexistence region of two phases.