It's related with ceramic engineering but you have to understand by yourself

1. Solid State Synthesis and
characterisation
Dr. Fayaz
Hussain

4. KNN-based Piezoelectric ceramics
Detail practical examples KNN and its batch calculations

7. BT

8. PZT
MPB= Morphotropic Phase
Boundary

9. ɛr-T relationship of KNN with excess addition of K and Na

10. The exact room-temperature crystal structure of sodium bismuth titanate has been a matter of debate for several
years.
NBT or BNT
http://abulafia.mt.ic.ac.uk/shannon/ptable.php
For ionic radii :