First-Principles Prediction of a 2D non-centrosymmetric Al2O3 with Tunable Piezoelectric and Electric-Field-Responsive Properties

Abstract

We predict a novel 2D non-centrosymmetric Al2O3 (NCS-Al2O3) using first-principles calculations combined with the MAGUS structure search package. This puckered hexagonal structure, featuring an "O-Al-O-Al-O" stacking sequence, exhibits exceptional stability with a formation energy of -2.88 eV/atom, surpassing that of a previously reported planar monolayer phase (-2.39 eV/atom) and closer to the bulk α-Al2O3 value (-3.16 eV/atom). It is an indirect bandgap semiconductor (3.98 eV) with intermediate mechanical stiffness and relatively strong anisotropy (AU ~ 7.99). Crucially, the broken inversion symmetry enables a strong in-plane piezoelectricity (~ 0.6 C/m2). Most significantly, an out-of-plane electric field can reversibly switch the NCS-Al2O3 between centrosymmetric and non-centrosymmetric states by modulating a low energy barrier (~ 0.11 eV). This unique electric-field-responsive behavior, coupled with its high stability and piezoelectricity, positions NCS-Al2O3 as a promising candidate for applications in 2D electronics, in-plane piezoelectric sensors, and electric-field-gated non-volatile memory devices.