Ferroelectricity in Aurivillius layer type structure ceramics with cationic substitutions in Bi/Sr

Ferroelectricity in Aurivillius typo structure ceramics based on the compos ition Bi2SrNb2O9 with cationic isomorphic substitutions in both the (Bi2O2) (2+) and the perovskite layers, Bi2-xTexSr1-xNa(K)(x) Nb2O9, has been obtai ned. Dielectric measurements as a function of the temperature show a first peak in the dielectric constant that would correspond to a ferroparaelectri c phase transition which temperature increases when the ionic radius size o f the Sr substitution dc decreases, and a higher temperature second peak wh ich behaviour could correspond to a relaxer ferroelectric. The results of m easurements of remanent polarization as a function oi the temperature seem to confirm this assumption because the polarization disappears at temperatu res that lay between those of the dielectric peaks. Well saturated hysteres is loops were obtained for the three substituted samples at temperatures ab ove 200 degrees C. The a.c. electric conductivity shows anomalies at temper atures closer to those of the remanent polarization disappearance. From d.c , electric conductivity, and frequency of the imaginary parts of the impeda nce and the dielectric modulus maxima as a function of the temperature data , activation energies are obtained that could correspond to thermally activ ated oxygen vacancies.