Al3+ doping-induced proton spatial inversion symmetry breaking in two-dimensional vermiculite: Intrinsic polarization and ferroelectric switching

To elucidate the origin of ferroelectric properties and underlying mechanisms in experimentally discovered two-dimensional (2D) vermiculite, we performed first-principles calculations on structures with varying Al3+ doping concentrations in the Mg–O octahedra. Our results reveal that intrinsic ferroelectricity stems from Al3+ induced proton symmetry breaking. Ferroelectricity emerges with doping along the x-direction, while doping along the y-direction produces antiferroelectricity. This direction dependence arises because the ferroelectric phase along y experiences stronger short-range ionic repulsion, forcing adjacent dipoles into antiparallel alignment to minimize close ionic contacts. Furthermore, the 2D vermiculite exhibits both in-plane and out-of-plane polarization, with components of 1.47, 1.37, and 0.63 e Å/proton and 0.18, 0.17, and 0.12 e Å/proton, respectively. The formation of a local dioctahedral configuration effectively reduces the ferroelectric switching barrier. Additionally, we designed 1D and 3D-P vermiculite structures to preserve semiconductor properties while mitigating the depolarization effect inherent in the antiferroelectric configuration. Compared to traditional perovskite materials, vermiculite demonstrates superior ferroelectricity and greater robustness during switching. These attributes position 2D vermiculite as a promising candidate for developing low-cost, high-performance room-temperature ferroelectric materials.