PEROVSKITE-RELATED PHASES IN THE SR4NB4O14-SR5NB4O15-SRTIO3 SYSTEM

Phase relations have been investigated within the Sr4Nb4O14-Sr5Nb4O15- SrTiO3 region of the SrO-Nb2O5-TiO2 system with a view to clarifying t he occurrence of perovskite-related phases, Most samples were prepared from oxide or carbonate powders heated in air at 1350 degrees C but s ome samples were also prepared by argon are melting. Overall phase ana lysis mas carried out by powder X-ray diffraction. Two phase lines con tain a homologous series of layered perovskite phases, These are the S r-n(Nb, Ti)(n)O3n+2 (4 less than or equal to n less than or equal to 7 ) series on the Sr4Nb4O14-SrTiO3 line and Sr-n(Nb, Ti)(n-1)O-3n (5 les s than or equal to n less than or equal to 7) on the Sr5Nb4O15-SrTiO3 line. The microstructures in these homologous series were clarified by transmission electron microscopy. This revealed both ordered and diso rdered intergrowths of the perovskite homologues and allowed the defec t microstructure of SrTiO3 in contact with the layered perovskites to be determined. (C) 1998 Academic Press.