Room temperature crystal structure and relaxor ferroelectric behavior of Pb0.5Ca0.5TiO3

Superlattice reflections observed for the first time in the room temperature powder neutron diffraction patterns of (Pb0.5Ca0.5)TiO3 (PCT50) are shown to arise due to an orthorhombic distortion (space group Pbnm) resulting from tilted TiO6 octahedra and off-center location of Pb2+/Ca2+. From a study of the temperature dependence of the rear and imaginary parts of the dielectric constant at various frequencies, PCT50 is found to be a relaxer ferroelectric. It is proposed that the structural frustration introduced by the tilted octahedra may be responsible for the relaxer behavior. (C) 1997 American Institute of Physics.