Mechanical properties of two-dimensional sheets of TiO2: a DFT study

Materials with a two-dimensional (2D) structure have emerged as an important component of modern technologies. Using 2D materials in many applications results in strain being created in the material. Materials respond to strain in different ways depending on their mechanical properties. The present work examines the mechanical properties of two 2D nanosheets of TiO2, namely hexagonal nanosheet (HNS) and lepidocrocite nanosheet (LNS). In order to accomplish this, we use the stress-strain theory in combination with first-principles density functional theory (DFT) calculations to investigate the mechanical characteristics, including stiffness constants, Young's modulus, Poisson's ratio, ideal strength, and critical strain. We validate our calculations by obtaining the important mechanical properties of bulk rutile TiO2 and comparing them with the theoretical and experimental values reported by others. Then, we compare the mechanical properties of TiO2 LNS and HNS using the same computational approach. It appears that LNS is stiffer than HNS, so we analyze structural differences between the two in order to determine the reasons for this. It has been observed that under small tensile strains, the responses, including induced stress, transverse contraction, and bond length change, are linear for both HNSs and LNSs. In general, LNS displays anisotropic responses, whereas HNS exhibits isotropic responses under small tensile strains and nearly isotropic responses under higher levels of strain. Finally, we compare the mechanical properties of HNS and LNS with those of graphene, h-BN, phosphorene, and hexagonal antimonene.