Pyrrole-like defects as origin of piezoelectric effect in nitrogen-doped carbon nanotubes

In this work, it is shown for the first time that nitrogen-doped carbon nanotubes (CNTs) exhibit anomalous piezoelectric properties that depend on the concentration of pyrrolic N, which can be used in the development of energy-efficient nanogenerators. The results are supported by studies of CNTs using X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and piezoresponse force microscopy. We proposed a mechanism for appearance of a piezoelectric response in CNTs associated with the formation of an uncompensated dipole moment as a result of curvature of the graphene sheet surface due to the formation of pyrrole-like defects and bamboo-like "bridges" in the nanotube cavity. It was found that with an increase in the concentration of pyrrolic N from 20 to 27 at. %, the magnitude of the piezoelectric strain coefficient of CNTs increases from 30 to 92 pm/V, and the magnitude of the current generated during the deformation of the CNTs increases from 16 to 129 nA. Experimental and theoretical estimates of the output voltage arising at 1% deformation of nitrogen doped CNTs are performed. The output voltage of CNTs ranged from 85 to 259 mV, depending on the pyrrolic N concentration. The established regularities make it possible to take into account the influence of the CNT defect types on its electrical properties in the process of creating various nanoelectronic devices. (c) 2022 Elsevier Ltd. All rights reserved.