Quasi-one-dimensional sliding ferroelectricity in NbI4

Sliding ferroelectricity was originally proposed to elucidate the\nout-of-plane polarization generated by a specific stacking arrangement of\nnon-polar van der Waals layers. However, the concept of sliding\nferroelectricity can be generalized to more geometries. Here, the NbI$_4$ bulk\nis theoretical demonstrated as a quasi-one-dimensional sliding ferroelectric\nmaterial, which exhibits a polarization of $0.11$ $\\mu$C/cm$^2$ perpendicular\nto the Nb's chains. The most possible ferroelectric switching path is found to\nbe via the interchain sliding along the chain direction, while other paths like\nPeierls-dimerization of Nb pairs may also work. Moreover, its polarization can\nbe augmented for $82\\%$ by hydrostatic pressure up to $10$ GPa, beyond which\nNbI$_4$ becomes a polar metal. In addition, the negative longitudinal\npiezoelectricity is also predicted.\n