A Origin of the polarization in BaTiO3 unit cell

[athosanian]

hi, in perovskite crystal, such as BaTiO3, due to the off-centre of Ti ion, there exists a polarization moment in the unit cell (as shown in below link). my question is: does the disposition of Ti atom lead to separation of electron cloud from the nuclei of the Ti atom and so the Ti atom plays as a electric dipole ?

https://www.comsol.com/blogs/piezoelectric-materials-crystal-orientation-poling-direction/

 

[Gigaz]

Not really. The Ti atom itself is in the 4+ state so that the whole unit cell acquires a dipole moment. You should probably look up the definition of the dipolar moment and calculate it for a perfectly symmetric and a distorted unit cell. Just think of the atoms as charged points. It is really that simple.

 

[athosanian]

so if the dipole moment of the unit cell is because the Ti atom is in 4+ state. So when is the Ti atom in the 4+ state ? for a perfectly symmmetric cell or distorted cell ?