The microstructure and dielectric properties of A-site excess and stoichiometric samples were investigated. Ruddlesden-Popper type planar faults in A-site excess specimens were observed by using high-resolution scanning transmission electron microscopy. Scanning transmission electron microscopy micro-chemical analysis, calculation of high-resolution images using a multi-slice method, and structural energy calculations, revealed that Ca ions selectively occupied the cation sites of the faults. An observed shift of the peak dielectric constant to lower temperatures, and an expansion of the lattice parameter of the A-site excess specimens, were attributed to selective occupation of the cation sites of the planar faults by Ca ions.

M.Fujimoto, T.Suzuki, Y.Nishi, K.Arai, J.Tanaka: Journal of the American Ceramic Society, 1998, 81[1], 33-40