Fe3+/Nb5+ co-doping effects on the properties of Aurivillius Bi4Ti3O12 ceramics

Highlights: • The co-substitution of Fe/Nb by Ti in Bi₄Ti₃O₁₂ produces multiferroic behavior. • The dielectric constant and loss tangent decrease with Fe/Nb content. • The transition temperature decreases with doping. • The switching behavior indicates ferroelectricity at room-temperature. • Magnetic measurements indicate antiferromagnetic spin correlations. Bi₄Ti_3-x(Nb_0.5Fe_0.5)_xO₁₂ (BTFNx) ceramics with 0 ≤ x ≤ 2 were synthesized to evaluate the effect of Fe³⁺/Nb⁵⁺ co-substitution into the B-site of Bi₄Ti₃O₁₂ (BIT). We show that the XRD pattern for the compounds with x ≤ 1 is the characteristic one of a layered perovskite structure belonging to the n = 3 member of the Aurivillius family. Impurity peaks assigned to a pyrochlore phase are detected at higher concentrations. Raman measurements corroborated that Fe³⁺and Nb⁵⁺ ions are incorporated into the Ti sites of the Aurivillius compound. Frequency dependent dielectric studies at room-temperature displayed the reduction of both dielectric constant and loss tangent with substitution, while the electric-field-induced polarization switching behavior indicates ferroelectric character. It is observed that the ferroelectric transition temperature decreases with increasing Fe/Nb content. Magnetic measurements indicated no evidence of ferromagnetic ordering, but antiferromagnetic spin correlations between Fe³⁺ ions.