Ferroelectric polymorphic phenomena in the layered antiferromagnet Cu(OH)2.

Ferroic orders and their associated structural phase transitions are paramount in the understanding of a multitude of unconventional condensed matter phenomena. On this note, our investigation focuses on the polymorphic ferroelectric phase transitions of Copper(II) hydroxide, Cu(OH) 2 , considering an antiferromagnetic ground state. By employing the first-principles studies and group theory analysis, we have provided a systematic theoretical investigation of vibrational properties in the hypothetical Cmcm high-symmetry phase to unveil the symmetry-allowed ferroic phases. We identified a non-polar to polar (Cmc2 1 ) phase transition, in which the displacive transformation is primarily responsible for the phase change induced by two B 1u (i.e. Γ - 2 ) phonon modes within the centrosymmetric phase. We also observed the existence of two polar structures with the same space group and different degrees of polarization (i.e P s = 3.06 µC.cm -2 and P s = 42.41 µC.cm -2 ), emerging from the high symmetry non-polar structure. According to the structural analysis the ferroelectric order, of a geometric nature, is driven by the Γ - 2 mode in which the O- and H sites displacements lead the polar distortion with a minor contribution from the Cu-sites. Interestingly, the 3d 9 :Cu 2+ Jahn-Teller distortion coupled with the orientational shifts of O-H atoms enhances the polarization.&#xD.