To evaluate the effects of porosity and grain size on relative
dielectric constant and piezoelectric constant d33, Fig. 7
illustrates the relationship. Fig. 7(a) shows an approximately
linear dependence of relative dielectric constant on porosity
while in Fig. 7(b), the correlation of d33-grain size is exactly the
same with that of d33-sintering temperature. These figures
attested to the primary dependence to a certain extent.
Admittedly, detailed relationship of these two pairs, i.e.,
dependence of d33 on grain size and relative dielectric constant
on porosity, should be further investigated by firstly ruling out
the influence of each other. It has been an effective attempt to
control grain size and porosity respectively to examine and
demonstrate the underlying effects [9].
It was noted in this study that the sintering temperature
1150 8C was enough for full sintering of the samples.
Consequently, the value of HFOM could be maximized at
this temperature according to the result. However, the relative
dielectric constant, which was proportionally related to the antiinterference ability of the samples, was at its lowest value at this
temperature. Therefore, a compromise should be made when
deciding the sintering temperature to achieve optimum values
of piezoelectric properties and relative dielectric constant
simultaneously.