CRYSTALLOGRAPHIC STUDY ON THE TERMS N=4,5 AND 6 OF THE SERIES (LA,CA)NTINO3N+2, (ND,CA)NTINO3N+2 AND CAN(TI,NB)NO3N+2

The homologous phases corresponding to the formula AnBnO3n+2 observed in the systems: La2Ti2O7CaTiO3, Nd2Ti2O7CaTiO3 and Ca2Nb2O7CaTiO3, have a structure derived from the structure of perovskite by periodic crystallographic shears, which delimitate n octahedra thick sheets. In the [0 1 0]* direction, the sheets are following each other with two types of arrangement. Crystals of terms n = 4,5, 5 and 6 were investigated by X-ray diffraction. According to the type of arrangement of the sheets, the phases studied have either an orthorhombic symmetry or a monoclinic symmetry, this last one giving rise to merohedral twins. © 1979.