Dielectric Permittivity and Magnetoelectric Coupling in Multiferroic ${\hbox {BiFeO}}_{3}$ and $({\hbox {Bi}}_{0.95}{\hbox {La}}_{0.05}){\hbox {FeO}}_{3}$ Ceramics

Dielectric permittivity and loss of BiFeO
₃
(BFO) and 5 mol% lanthanum-substituted BFO [(Bi
_0.95
La
_0.05
)FeO
₃
or BFO-5% La] ceramics have been carried out as functions of temperature and frequency. A frequency-dependent and broad dielectric shoulder and maximum were observed in BFO and BFO-5% La near 600-700 K. These dielectric responses are likely due to the magnetoelectric coupling while the antiferromagnetic-paramagnetic transition takes place near the Néel temperature. As an approximation, a barrier model with intrinsic barriers B (in temperature unit) every lattice constant
a
and extrinsic barriers B +Δ every distance
d
is introduced to describe the low-frequency upturn in dielectric loss in the high-temperature region. Good qualitative fits are obtained for BFO and BFO-5% La. This work suggests that 5 mol% La substitution can enhance dielectric response and considerably reduce electric conductivity.