Two-dimensional V-shaped PdI2: Auxetic semiconductor with ultralow lattice thermal conductivity and ultrafast alkali ion mobility

Abstract

Using first-principles calculations, we predicted a multifunctional two-dimensional (2D) semiconductor PdI2 from its van der Walls layered bulk. Monolayer or multilayer PdI2 obtained by mechanical exfoliation exhibit high stability as freestanding 2D materials. Originating from its special corner-shared quasi-plane crystal structure, an amazing in-plane negative Poisson's ratio in monolayer PdI2 has been confirmed. The layer dependent electronic and thermal properties have also been discussed in detail. Encouragingly, it has been found that strong phonon scattering which is induced by low symmetry will further reduce the lattice thermal conductivity in monolayer PdI2 at room temperature. Besides, the monolayer PdI2 is seen as an excellent platform for alkali ions migration with ultralow diffusion barriers, benefiting from its distinctive V-shaped crystal structure. Considering these interesting findings, we believe the 2D PdI2 will be a promising candidate for future's low dimensional electron devices.