Ferroelectricity is a property of certain materials that exhibit a spontaneous electric polarization that can be reoriented by an external electric field. This means that, unlike ordinary dielectric materials that only polarize in response to an applied electric field, ferroelectric materials can maintain a permanent electric polarization even when the external field is removed.
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The existence of a spontaneous electric polarization that can be reversed by an applied electric field. A polar material is not necessarily switchable under useful conditions.