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 tiltedTiO6octahedra and off-center location ofPb2+/Ca2+. From a study of the temperature dependence of the real and imaginary parts of the dielectric constant at various frequencies, PCT50 is found to be a relaxor ferroelectric. It is proposed that the structural frustration introduced by the tilted octahedra may be responsible for the relaxor behavior.©1997 American Institute of Physics.