Integrated Computation and Experimental Investigation on the Adsorption Mechanisms of Anti-Wear and Anti-Corrosion Additives on Copper

We integrated first-principles calculations and surface characterization techniques to reveal a new molecular adsorption mechanism of antiwear (dialkyl dithiophosphate ester, EAK) and anticorrosion (2,5-bis­(ethyldisulfanyl)-1,3,4-thiadiazole, DTA) additives on the Cu surface during the rolling process. For direct comparison of modeling and experiments, the Cu(110) surface was used in the model based on the strong (220) preferred orientation observed in the microstructures of the rolled copper foil. Density functional theory (DFT) calculations were performed to obtain the adsorption energy, the optimized adsorption structures, and the charge transfer due to adsorption for EAK and DTA on the Cu(110) surface. It was found that the anticorrosion additive, DTA, decomposed and chemically adsorbed on the Cu(110) surface strongly via multiple Cu–N and Cu–S bonds, while the antiwear additive, EAK, adsorbed weakly due to one Cu–O bond. The predicted chemical bonds formation with the Cu surface reasonably agreed with X-ray photoelectron spectroscopy (XPS) analysis. A new anticorrosion mechanism, due to DTA decomposition and stronger chemisorption than that of EAK, was therefore proposed based on the simulation

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO₃) with a special thermomechanical treatment (TMT), where BaTiO₃ nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials