Ferroelectricity is an electrical phenomenon whereby certain materials may exhibit a spontaneous dipole moment the direction of which can be switched between equivalent states by the application of an external electric field. The internal electric dipoles of a ferroelectric material are physically tied to the material lattice so anything that changes the physical lattice will change the strength of the dipoles and cause a charge to flow into or out of the ferroelectric material (see discussion below) even without the presence of an external voltage across the capacitor