= Solution
<Barium titanate> has a high-temperature cubic <perovskite structure>, with Ti centred in its <oxygen> octahedron on average. This phase is <paraelectric>. Near room <temperature> the structure is tetragonal, with relative ionic displacements that give a spontaneous <electric polarization>. This phase is <ferroelectric>: an applied <electric field> can switch between differently polarized domains. Both phases have the same composition, BaTiO$_3$; the transition near $120\,{}^\circ\mathrm{C}$ changes <crystal symmetry> and electrical response.
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