Inducing ferroelectricity in NH$_4$I and NH$_4$Br via partial replacement of protons by deuterons

TL;DR

This study demonstrates that partial replacement of protons with deuterons in NH$_4$I and NH$_4$Br induces reversible ferroelectricity in their ordered gamma phases, suggesting new pathways for hydrogen-based ferroelectric materials.

Contribution

It introduces a novel method to induce ferroelectricity in ammonium halides through partial deuteration, expanding the functional properties of hydrogen-based materials.

Findings

Reversible electric polarization observed in deuterated ammonium halides.

Partial deuteration causes asymmetric lattice distortions linked to magnetic moments.

Provides an alternative approach to achieve ferroelectricity in non-polar polymorphs.

Abstract

While all of the polymorphs of NH$_4$I and NH$_4$Br are non-polar, a reversible electric polarization is established in the ordered $\gamma$ phases of (NH$_4$)$_{0.73}$(ND$_4$)$_{0.27}$I and (NH$_4$)$_{0.84}$(ND$_4$)$_{0.16}$Br (where D is $^2$H) 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.