Influence of Bi-site substitution on the
ferroelectricity of the Aurivillius compound
Bi2SrNb2O9
P. Durán-Martin, A. Castro, P. Millán, B. JimÈnez
(CSIC)
Ceramics
based on the composition
Bi2SrNb2O9
with isomorphic substitutions of cations in the
Bi2O2
perovskite layers
Bi2-xTex-Sr1-xNa(K)xNb2O9,
have been prepared by solid state reaction. The ferroelectricity of these
Aurivillius type structures has been studied. Dielectric measurements
as a function of the temperature show a low temperature maximum in the
dielectric constant that would correspond to a ferro-paraelectric phase
transition. The temperature of this maximum increases when the radius of
the ion that substitutes Sr for decreases. A second maximum in the
dielectric constant is found at higher temperature possibly corresponding
to a relaxor ferroelectric. Measurements of remanent polarization as a
function of the temperature seem to confirm the relaxor behavior, because
the polarization disappears at temperatures between the two maxima of the
dielectric constant. Saturated hysteresis loops are obtained for all
the substituted samples at temperatures above 300°C. Ferroelectric
parameters such as the polarization, coercive field and coupling factors
of the BSN family compounds were obtained for the first time.
The a.c. electric conductivity shows anomalies at temperatures close to
those where the remanent polarization disappears. Activation energies
calculated from measurements of d.c. electric conductivity, impedance arcs
and dielectric modulus data may be associated with thermally activated
oxygen vacancies.
Order No.:
JA809-031 © 1998 MRS
Go to September 1998 Table of Contents
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