LAYERED PEROVSKITE PHASES IN THE ND2TI2O7-SRTIO3 SYSTEM

The layered perovskite structures formed when samples with overall com positions in the range Nd2Ti2O7 - SiTiO3 (more correctly Nd4Ti4O14 - S rTiO3) were argon are melted have been investigated via powder X-ray d iffraction and high resolution transmission electron microscopy. With the addition of SrTiO3 the Nd4Ti4O14 composition is moved towards that of SrNd4Ti5O17 by the incorporation of perovskite-like lamellae 5 oct ahedra thick in place of lamellae 4 octahedra thick found in the paren t phase. These additional lamellae are often ordered despite the non-e quilibrium preparation technique used. The phase SrNd4Ti5O17 was prepa red and is reported for the first time. The diffraction patterns of th is material always showed a wavy quasi-sinusoidal streaking which has been attributed to the presence of a compositionally modulated lattice . No ordered structures corresponding to the n = 6 phase were found al though isolated lamellae six octahedra in thickness were observed inte rgrown in a disordered fashion in the n = 5 structure. In general such disordered material coexisted with SrTiO3.