Hey, I am confused, what is the exact reason for the appearance of a voltage upon a mechanical stress at a ferroelectric material like a BaTiO3 Perovskite? Below the Curie temperature the structure is no more cubic but tetragonal, lets say c-site is now longer than a- and b-site. And of course there is a polarization in each unit cell now. Ok, now we do mechanical stress at the material. I assume there are many contribution for the resulting increase of net polarization: First, we do the same as we do at a piezo crystal (quartz), every single dipole in every unit cell gets stretched. Therefore, the whole body get stretched. And the polarization increases. Secondly, we do streched the random aligned domains! In every ferroelectric there are domains with mutual aligned inner polarizations. When c-site is longer than a and b, and we put a stress from c site, the unit cell should move 90° right? You can imagine hundred pens. When you grab them, they will align! So, the "body of pens" will strain in the "long-direction", thus we have a bigger net polarization due to the alignment of every unit cell / pen in c-direction. The central issue is: Do the second point make a large strain? Or is the second point just describing the phenomenon of electrostriction? Or, none of them (or a mixture): There are domains, the induced stress let the domain move and therefore we can now do point 1: streching them! Do the movement of domains itself lead to a higher polarization (because c-site itseld is longer), or is the movement a condition for a higher polarization due to the further streching of the c-site? Thank you !!