Journal of the American Ceramic Society, Vol.87, No.4, 677-682, 2004
Isomorphic A-site substitution on sillenite-type compounds
Investigations of A-site substitution in sillenite-type compounds showed that only a substituent ion with a lone-electron pair can be successfully incorporated onto the A-site in place of Bi3+. This is because the stability of sillenite structural polyhedra is conditioned by the presence of a stereochemically active lone-electron pair. Accordingly, the substitutional experiments combined with an X-ray diffraction analysis, energy- and wavelength-dispersive microanalysis, and Rietveld refinement showed that Nd3+ and La3+ ions, which do not possess a lone-electron pair, cannot be incorporated into the sillenite-type structure above the detection limits of the applied analytical techniques. In contrast, the A-site substitution of Pb2+, Tl+, and Sb3+ ions, which do possess a lone-electron pair, was experimentally confirmed. Te4+ also possesses a lone-electron pair, but the substitutional experiments showed that this ion did not incorporate into the sillenite structure.