Relaxor-like and spectroscopic properties of niobium modified barium titanate

Abstract:

Dielectric susceptibility measurements on niobium-modified barium titanate ceramics for Nb compositions extending up to the solubility limit (18%) show that these materials display relaxor-like properties for compositions larger than ∼ 6% Nb. Raman spectra exhibit extra modes attributed to local responses related with the substitution of niobium for titanium ions. The behaviour of this barium titanate modification, in which Nb⁵⁺ aliovalent cations are substituted for Ti⁴⁺, is discussed by comparison with the zirconium-modified series, in which, oppositely, only a size difference characterizes the substitution on the B site. It is emphasized that electrical random fields created in the former case are more efficient in inducing a relaxor behaviour than elastic random fields created in the latter. The nature of the complex defects expected from the inherent high concentration of barium vacancies is discussed in connection with photoluminescence spectra.