Ferroelectric Behavior of a Hexamethylenetetramine-Based Molecular Perovskite Structure.

We report the development of a molecular ferroelectric material inspired by the hexamethylenetetramine (hmta) non-centrosymmetric molecular rotator. The bromide salt of diprotonated hmta (hmtaH ) crystalized as (hmtaH )(NH )Br in a metal-free ABX perovskite-type structure, in which the A and B sites are occupied by hmtaH and ammonium cations, respectively. The compound crystallized in the Pma2 polar space group. A distorted polar perovskite structure formed owing to the distortion of {(NH )Br } octahedrons that are stabilized through the formation of NH⋅⋅⋅Br hydrogen bonds and the orientational ordering of positive charges on the non-centrosymmetric hmtaH molecules. This spontaneous polarization exhibited ferroelectric behavior with a nominally high Curie temperature (>400 K), in which the electrical switching of polarization originates from the rotation of the hmtaH unit.