Tribology-Induced Tunability in the Piezoelectricity of 2D CaO Bilayers: A First-Principles Study

In the present era of nanotechnology, converting tiny mechanical stimuli into electrical energy to make energy-harvesting devices has gained significant research attention. Low-power electronics, sensors, actuators, and robotics can now be easily powered using nanogenerators based on triboelectric, and piezoelectric effects. On the other hand, due to the strong difference in electronegativity and superior non-centrosymmetricity, two-dimensional (2D) Calcium Oxide (CaO) is expected as a promising candidate for nano-energy-harvesting devices. This study uses first-principles calculations to explore the tribological effect-induced piezoelectric properties of 2D CaO bilayers and check their suitability for nanogenerator applications. Two types of tribological effects such as horizontal sliding motion and vertical compression are used in bilayer CaO to explore their piezoelectric properties including, potential energy, polarization deviations, charge density, shear strength, induced voltage, and power density. Results indicate that when the bilayer structure slides from A-B to A-A staking pattern, there occurs a substantial increase in potential energy, polarization profile, and charge gain. Moreover, due to the reduction of interlayer spacing a maximum induced voltage of 0.165 V is found for bilayer 2D CaO. Finally, a compressive-sliding motion-based nanogenerator model is proposed for a 2D CaO bilayer structure that can produce an output power density of up to 142 mWcm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup>.