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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Crystallography

Background:

• Ferroic orders and structural phase transitions are key to understanding exotic condensed matter phenomena.
• Copper(II) hydroxide (Cu(OH)2) exhibits polymorphic ferroelectric (FE) phase transitions, particularly with an antiferromagnetic ground state.

Purpose of the Study:

• To theoretically investigate the ferroelectric phase transitions in Cu(OH)2.
• To identify symmetry-allowed ferroic phases from a hypothetical high-symmetry Cmcm phase.
• To understand the microscopic mechanisms driving ferroelectricity in Cu(OH)2.

Main Methods:

• First-principles calculations.
• Group theory analysis.
• Vibrational property analysis of the Cmcm phase.

Main Results:

• Identified a non-polar to polar (Cmc21) phase transition.
• Displacive transformation induced by two B1u (Γ2-) phonon modes.
• Observed two polar structures with varying polarization (3.06 and 42.41 µC·cm⁻²).
• Ferroelectric order is primarily driven by O- and H-site displacements, with minor Cu-site contribution.
• Jahn-Teller distortion in Cu2+ and O-H shifts enhance polarization.

Conclusions:

• The study elucidates the mechanism of ferroelectric phase transitions in Cu(OH)2.
• Geometric ferroelectric order is confirmed, driven by specific phonon modes and atomic displacements.
• The findings contribute to the understanding of ferroelectricity in hydroxide materials.