Strain induced quadratic effect on polarization and electronic structure of ferroelectric Cu(OH)2

Copper (II) hydroxide, Cu(OH)2, as a member of the metal hydroxide family, has recently been identified as a new layered magnetically-active ferroelectric material, broadening its potential functional properties. Herein, we investigate, by means of first-principles calculations and theoretical analysis, the ferroelectric polarization, piezoelectric properties, and the electronic structure of two polar polymorphs of copper (II) hydroxide under epitaxial strain, as a tuning mechanism. The applied in-plane xy-epitaxial strains on the two orthorhombic polar phases, conserves the Cmc21 space group. We observed interesting nonlinear and parabolic piezoelectric phenomena induced by the epitaxial strain. Our calculations predict this as an indirect wide bandgap (WBG) semiconductor and variation of band gap as a function of epitaxial strain is also presented. To prevent current leakage, the piezoelectric material must be a semiconductor, and the polar phases remain robust semiconductor under the given strain range. Finally, we show that the spontaneous polarization increases under compressive whereas it is suppressed under tensile strain. The latter is explained in terms of the associated structural distortion and eigendisplacements.