Ferroelectric Behavior of a Hexamethylenetetramine‐Based Molecular Perovskite Structure

Abstract

Abstract 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 2 ) crystalized as (hmtaH 2 )(NH 4 )Br 3 in a metal‐free ABX 3 perovskite‐type structure, in which the A and B sites are occupied by hmtaH 2 2+ and ammonium cations, respectively. The compound crystallized in the P ma2 polar space group. A distorted polar perovskite structure formed owing to the distortion of {(NH 4 )Br 6 } octahedrons that are stabilized through the formation of NH⋅⋅⋅Br hydrogen bonds and the orientational ordering of positive charges on the non‐centrosymmetric hmtaH 2 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 2 unit.