Analysis of planar defects in Nb sub(2)O sub(5)- and Bi sub(2)O sub(3)-doped BaTiO sub(3) ceramics

The structure and chemistry of planar defects in Nb sub(2)O sub(5)- and Bi sub(2)O sub(3)-doped BaTiO sub(3) ceramics that exhibit `core-shell' microstructures have been examined using a combination of conventional transmission (CTEM) and high-resolution (HREM) and scanning transmission (STEM) electron microscopy and microanalysis. In addition to ferroelectric domain boundaries within the core, twins and `stacking faults' were observed, both with interface planes lying along {1 1 1}. Unlike the twins, stacking faults were observed only within the paraelectric shell region of the BaTiO sub(3) grain; these planar defects are enriched in Nb and Bi relative to the surrounding matrix. The combined CTEM contrast analysis and HREM observations suggest a fault displacement vector normal to the fault plane of magnitude 1/2 < 1 1 1 > +x < 1 1 1 > (x identical with 0.1); a proposed fault structure is based on a double BiO super(3) sub(3) super(-) layer with bismuth cations occupying barium sites and charge compensation by Nb super(5+) substitution in adjacent octahedral sites. In addition, the incorporation mechanism of Nb sub(2)O sub(5) and Bi sub(2)O sub(3) into BaTiO sub(3) is discussed with respect to microanalysis results.