POLYTYPE STRUCTURES IN LEAD-CALCIUM TITANATE CERAMICS

High resolution transmission electron microscopy (HRTEM) was used to i nvestigate the ion ordering structures of lead-calcium titanate (Pb0.5 Ca0.5)TiO3. The results show that apart from the presence of 1/2{111}, 1/2{110} and 1/2{100} superstructures, there is a 1/4{110} modulation structure coexisting in (Pb0.5Ca0.5)TiO3. The characteristics of the 1/4{110} modulation structure were determined at the lattice level. Pr obable arrangements of the atoms in the atomic layers in the modulatio n structure were suggested.