Effect of cationic substitutions on ferroelectric properties of Pb5Ta10O30: Generation of the relaxor behavior

New compositions derived from Pb5Ta10O30 have been synthetized to study the influence of cationic substitutions [heterovalent (Pb2+ --> La3+ and Pb2--> K+) and homovalent (Pb2+ --> Ba2+ and Pb2+ --> Ca2+)] on its ferroelect ric properties. The ferroelectric behavior of each composition was evidence d by way of dielectric measurements as a function of both temperature and f requency. Structure determinations and refinements were also performed to d etermine which crystallographic sites are occupied by the substituted catio ns, Whatever the nature of the substitution, the relaxer behavior is induce d by a weak rate of substitution, Furthermore, except in the case of the ca lcium-containing composition, no significative difference was found concern ing crystallographic data. All the results obtained are compared with those described in the literature and discussed in terms of charge, ionic radius , and steric effect. (C) 2001 Academic Press.