Cationic ordering structures of lead magnesium niobates with isovalent dopants having different ionic radii

Abstract

Pyrochlore-free lead magnesium niobate ceramics, the lead of which is partly replaced by lanthanum, and the magnesium of which is partly replaced by isovalent dopants such as nickel and cadmium, having different ionic radii < r(Ni2+) (0.69 Angstrom) < r(Mg2+) (0.72 Angstrom) < r(Cd2+) (0.95 Angstrom)}, Pb0.9La0.1[(Mg0.8Ni0.2)(1.1/3)Nb-1.9/3]O-3 and Pb0.9La0.1[(Mg0.8Cd0.2)(1.1/3)Nb-1.9/3]O-3,O- were fabricated and their B-site cationic ordering structures were investigated by X-ray diffractometry and transmission electron microscopy. Both these techniques revealed that the lead-lanthanum-magnesium niobate modified by cadmium has a higher degree of nonstoichiometric I:l-ordering than that modified by nickel. The results were discussed on the basis of the larger ionic size difference between B&apos;- and B "-site cations in A(B-1/3&apos;B-2/3("))O-3-type perovskite structure of lead-lanthanum-magnesium niobate modified by cadmium than that modified by nickel.