Monolayer group-V binary compounds ψ -BiP and ψ -SbP with ultrahigh piezoelectricity and stability

Abstract

Two-dimensional (2D) binary compound materials composed of group-V elements are hot spots owing to the unique easy-to-design symmetry-broken structures and excellent physical and chemical properties. In this paper, the stability and corresponding piezoelectric properties of group-V binary compounds $AB$ ($A,B=\text{N}$, P, As, Sb, Bi, and $A\ensuremath{\ne}B$) with different structure phases are systematically investigated by performing first-principles calculations. The calculations show that the group-V binary compounds always exhibit six types of a structure phase with a relative low energy, i.e., $\ensuremath{\alpha}$, $\ensuremath{\beta}$, $\ensuremath{\gamma}$, $\ensuremath{\delta}$, $\ensuremath{\lambda}$, and $\ensuremath{\psi}$ phases. More interestingly, compared to the obvious piezoelectric effect reported in the $\ensuremath{\alpha}$ phase of group-V binary compounds, a giant piezoelectric coefficient is revealed in $\ensuremath{\psi}$-SbP and $\ensuremath{\psi}$-BiP, where ${\mathit{d}}_{11}$ is evaluated as high as 263.77 and 298.48 pm/V, respectively. Such a superb piezoelectric performance in $\ensuremath{\psi}$-SbP and $\ensuremath{\psi}$-BiP even exceeds the previously reported 2D piezoelectric material SnSe (${\mathit{d}}_{11}=250.58$ pm/V), which is mainly originated from a unique flexible structure and special symmetry. The mechanical, dynamical, and thermal stabilities of $\ensuremath{\psi}$-BiP and $\ensuremath{\psi}$-SbP are verified by the Born-Huang criterion, phonon spectrum, and ab initio molecular dynamics simulations. The findings presented in this paper shed light on the structure and piezoelectric properties of group-V binary compounds, and provide valuable guidance for their potential applications in flexible sensors and the energy harvesting community.