Coexistence of out-of-plane and in-plane ferroelectricity in ultrathin elemental group-V nanotube arrays
Yuwen Zhang, Chunfeng Cui, Chaoyu He, Tao Ouyang, Jin Li, Chao Tang
Abstract
The rare and abnormal elemental ferroelectricity has been predicted and realized in group-V monolayers in recent years [Xiao et al., Adv. Funct. Mater. 28, 1707383 (2018); Gou, Nature (London) 617, 67 (2023)]. However, the valuable out-of-plane (OOP) ferroelectricity is missing in these monolayers owing to the symmetry of the glide plane. In this article, the low-energy nanotube arrays (NTs) of group-V elements (P, As, Sb, and Bi) are carefully confirmed to be ferroelectric materials with both OOP (0.15--0.43 pC/m) and in-plane (IP, 0.52--6.63 pC/m) spontaneous polarizations. The spontaneous polarization originates from the asymmetric electron distribution caused by the noncentrosymmetric tubular crystal structure. Meanwhile, benefited by the coexistence of OOP and IP polarizations, such tubular crystal structure also exhibits unique quadruple polarization states. The lower switching barriers between the logic states (ranging from 13 to 93 meV/atom) further indicate that they are easily controlled by external electric fields, facilitating efficient data read and write operations. These characteristics lay the foundation for their application in high-speed, low-power, and large-scale data storage. More interestingly, our calculations demonstrate that these NTs of group-V elements possess not only IP piezoelectricity comparable to ${\mathrm{MoS}}_{2}$ (0.95--7.97 pm/V) but also nonzero OOP piezoelectric coefficients (0.04--8.01 pm/V), further expanding their potential applications in energy conversion. It is anticipated that these discoveries will undoubtedly serve to catalyze further research and applications involving single-element materials within the domains of ferroelectricity-based information storage and piezoelectricity-based energy conversion.