The structure and chemistry of planar defects in Nb2O5- and Bi2O3-doped ceramics which exhibited so-called core-shell microstructures were analyzed by using a combination of conventional transmission electron microscopy, high-resolution transmission electron microscopy and scanning transmission electron microscopy and microanalysis. In addition to ferro-electric domain boundaries within the core, twins and stacking faults were observed; both with interface planes lying on (111). Unlike the twins, the stacking faults were observed only within the para-electric shell region of the grains. These planar defects were enriched in Nb and Bi, relative to the surrounding matrix. The observations suggested the existence of a fault displacement vector which was normal to the fault plane and had a magnitude of ½(111)+0.1(111). A fault structure was proposed which was based upon a double BiO33- layer, with Bi cations occupying Ba sites and with charge compensation by Nb5+ substitution at adjacent octahedral sites.

Analysis of Planar Defects in Nb2O5- and Bi2O3-Doped BaTiO3 Ceramics. M.A.McCoy, W.E.Lee, R.W.Grimes, R.Keyse: Journal of Materials Science, 1998, 33[24], 5759-71