Large out-of-plane piezoelectricity of oxygen functionalized MXenes for ultrathin piezoelectric cantilevers and diaphragms

• Published in: Nano energy Vol. 65; p. 104058
• Main Authors: Tan, Jie, Wang, Yunhua, Wang, Zongtan, He, Xiujie, Liu, Yulan, Wang, Biao, Katsnelson, Mikhail I., Yuan, Shengjun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-11-2019
• Subjects: MXenes; Out-of-plane piezoelectricity; Piezoelectric charge density; Piezoelectric diaphragm; Piezoelectricity; Piezoelectricity; Piezoelectric charge density; Piezoelectric diaphragm; Out-of-plane piezoelectricity; MXenes
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2019.104058

MXenes have currently drawn considerable attention in functional materials and energy storages, because of their versatile and excellent properties. However, few works have been made on Mxenes' piezoelectricity. Applying the density-functional theory, we show that M2CO2 (M = Sc, Y, La) MXenes possess large Poisson's ratio and in-plane piezoelectricity comparable to that of 2H-MoS2. Furthermore, M2CO2 MXenes have strong out-of-plane piezoelectricity, which is highly desirable for ultrathin piezoelectric devices (cantilever and diaphragm) with the d31 operating mode. For a MXene diaphragm the piezoelectricity-generated charges mainly concentrate in six areas, which are determined by the lattice symmetry. In particular, the in-plane piezoelectric charges are localized near the circular clamped boundary, whereas the out-of-plane piezoelectric charges are inside the pressure-induced bubble. Our observations propose a realistic way to collect the piezoelectricity-induced charges, making these systems very promising for energy harvesting and piezoelectric sensing.
The piezoelectricity, electronic structures and mechanical properties of M2CO2 MXenes are revealed by the first-principle calculations. Compared with other 2D materials, M2CO2 MXenes possess a higher vertical piezoelectricity and hence are suitable for ultrathin piezoelectric devices with d31 mode. The piezoelectric response analyses are further developed in MXene cantilever and diaphragm by virtue of the mechanical plate theory. The simulations shed new light on MXenes’ energy harvesting and piezoelectric sensing applications. [Display omitted]
•M2CO2 MXenes possess large in-plane piezoelectricity and stronger out-of-plane piezoelectricity.•M2CO2 MXenes have large Poisson's ratios, high elastic deformation range and relatively large band gaps.•The out-of-plane piezoelectric response theories have been developed for both MXene cantilever and diaphragm.