Planar faults in Aurivillius compounds:: an X-ray diffraction study

Layered bismuth-containing perovskites are known to be subject to complex structural imperfections such as planar faults. A careful analysis of X-ray powder diffraction lines of the Aurivillius compound SrBi2Nb2O9 shows that stacking faults are located along the c axis and (hk0) reflections are thus unaffected by faulting. In the [001] direction the profiles exhibit a Lorentzian shape and a 22 nm coherently diffracting domain size is found, which corresponds to a stacking-fault density of 0.032 nm(-1). The reciprocal-space mapping technique applied to epitaxial layers allows direct visualization of the highly anisotropic (001) reciprocal-lattice points. Because of the high counting rates and the lack of peak overlap in epitaxial layers, very subtle changes in the diffraction profiles can be measured as a function of thermal treatment time. Thermal annealing at 700degreesC up to 600 h reduces the stacking-fault density as attested by the strong increase in the domain size (198 nm) and the broadening of the domain size distribution. Additionally a significant lowering of the Lorentzian character of the diffraction profiles is found, in perfect agreement with the stacking-fault density reduction.