In previous studies, this kind of temperature dependence of
phase structure transition behavior was also observed. Researchers
attributed this phenomenon to the different extents of the
volatilization of alkali metal ions during sintering [13–16]. Except
for the above factor, we hold the point that this composition of
KNNLN lies in the vicinity of PPT region and the room temperature
phase of this composition would be very sensitive to the processing
parameters, such as sintering temperature, stress, compositional
segregation, and so on. The effects of these factors would be
discussed in the following content.