Inducing Ferroelectricity in NH₄I and NH₄Br via Partial Replacement of Protons by Deuterons

While all of the polymorphs of NH4I and NH4Br are nonpolar, a reversible electric polarization is established in the ordered gamma phases of (NH4)(0.73)(ND4)(0.27)I and (NH4)(0.84)(ND4)(0.16)Br (where D is H-2) via dc electric fields. The presence of two groups of orbital magnetic moments appears to be responsible for the asymmetric lattice distortions. Our findings provide an alternative pathway for hydrogen-based materials to potentially add a ferroelectric functionality.