Cation-deficient perovskite-related (Ba, La)(n)Tin-delta O3n (n >= 4 delta) microphases in the La4Ti3O12-BaTiO3 system: An HRTEM approach

The large nonstoichiometric domain, observed in the La4Ti3O12-rich part of the La4Ti3O12-BaTiO3 system, has been shown to correspond to a continuous s eries of cation-deficient perovskite-related (Ba, La)(n)Tin-deltaO3n (n gre ater than or equal to 4 delta) microphases. The crystal structures of these microphases have been analyzed by electron diffraction and high-resolution electron microscopy. They can be described as coherent intergrowths of P-p erovskite-like blocks La4Ti3O12 and Q-perovskite-like blocks BaLa4Ti4O15, r espectively, constitutive of the simple basic terms n = 4 and n = 5 of the previously identified (Ba, La)(n)Tin-1O3n series. The corresponding BaQLa4( P+Q)Ti3P+4QO12P+15Q microphases can thus be denoted by 4(P)5(Q) in a compac t form. In fact, only the 4(P)5(1) intergrowth sequences have been observed . Eight of these are clearly shown by direct imaging. No intergrowth terms were observed for compositions ranging from BaLa4Ti4O15 (n = 5) to Ba2La4Ti 5O18 (n = 6). The ability of the system to develop coherent intergrowths ha s been discussed in the light of information provided by an accurate analys is of crystal structures of the basic members of the series: La4Ti3O12 (n = 4), BaLa4Ti4O15 (n = 5), and Ba2La4Ti5O18 (n = 6). (C) 1999 Academic Press .