Lead-free relaxor ferroelectric materials have attracted attention
due to their field-induced phase transition and its associated strain,
which is an important feature in the use of an actuator [1e6]. Bibased
ferroelectric materials, BiNaTiO3eBaTiO3eKNaNBO3, BiNaKTiO3eBiAlO3,
and Ta-doped BiNaKTiO3, etc. [7e16] exhibited phase
transition with high fields of more than 6e7 kV/mm. To reduce the
field to complete the phase transition, we proposed a concept of an
inclusion-type composite, consisting of relaxor grains and ferroelectric
grains, showing a relatively low field-induced phase transition
[12]. An example describing our concept is shown in Fig. 1.
Fig. 1 shows the concept of an inclusions-embedded composite and
layered composite designed for improving the field-induced phase
transition and its associated deformation behavior. As seen in Fig. 1,
as an electric field was applied, the relaxor or non-polar phase of
the matrix is transformed into a ferroelectric phase. As a
consequence, the field-induced polarization change and strain
The composite concepts can be explained in terms of an
equivalent circuit. In viewing this composite in terms of an equivalent
circuit, this material can be expressed using a serial capacitor
model as shown in Fig. 1 [18e21]. In this case, if the dielectric
permittivity of the relaxor (non-polar) phase is lower than that of
the ferroelectric phase (inclusions and layer), the matrix receives a
higher field than the ferroelectric phase. As an even lower field was
applied to the composite, the matrix then experiences the transition
from relaxor to ferroelectric phases.
were observed