It knows that domain reorientation during the poling process
has direct influence on the macroscopic electrical properties of the
materials. Therefore, it became essential to investigate the
difference between the poled and unpoled samples. In Fig. 4 the
relative intensities of (0 0 2) and (2 0 0) of the samples after poling
differ great from the corresponding values of the samples before
poling. The relative intensity of (0 0 2) for the poled samples has
been promoted to different degrees. The change in the relative
intensities of (0 0 2) and (2 0 0) relates with the degree of domain
orientation: the more obvious the difference for the relative
intensities of (0 0 2) and (2 0 0) of the poled samples, the higher the
extent of 908 domain orientation. We have already established a
complete and accurate system to identify the percentage of 908
domain reorientation in the tetragonal phase of KNNLN ceramics
vs electric field, and the results could explain the change of
piezoelectric properties reasonably [18]. However, the essential
prerequisite of the above approach is that the phase structure of
KNNLN ceramics should be a pure T phase not a coexistence of T
and O phase. So it is still tough for us to precisely calculate the
percentage of 908 domains reorientation owing to the complexity
of mixed phase structure. Nevertheless, in order to simply deal
with this circumstance, we might roughly handle it. It is observed
that the relative intensity of (0 0 2) for 980 8C sintered sample after
poling is considerable stronger than these of the 1040 8C and
1080 8C sintered samples after poling. That is to say that the
samples for 980 8C could possess the best piezoelectric performance.
However, this is not the case. d33 of the 980 8C sintered
samples is lower than these of the other two kinds samples. Hence,
it is supposed that the change with the intensity of (0 0 2) during
poling was not just caused by the orientation of the 908 domain,
but also by the phase transition from T to O phase induced by the
poling process. And this point was also verified by previous
research [8].