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Ti-Al-O-N coatings were synthesized by cathodic arc and high power pulsed magnetron sputtering. The chemical composition of the coatings was determined by means of elastic recoil detection analysis and energy dispersive X-ray spectroscopy. The effect of oxygen incorporation on the stress-free lattice parameters and Young's moduli of Ti-Al-O-N coatings was investigated by X-ray diffraction and nanoindentation, respectively. As nitrogen is substituted by oxygen, implications for the charge balance may be expected. A reduction in equilibrium volume with increasing O concentration is identified by X-ray diffraction and density functional theory calculations of Ti-Al-O-N supercells reveal the concomitant formation of metal vacancies. Hence, the oxygen incorporation-induced formation of metal vacancies enables charge balancing. Furthermore, nano-indentation experiments reveal a decrease in elastic modulus with increasing O concentration. Based on ab initio data, two causes can be identified for this: First, the metal vacancy-induced reduction in elasticity; and second, the formation of, compared to the corresponding metal nitride bonds, relatively weak Ti-O and Al-O bonds. [ABSTRACT FROM AUTHOR]

Nitrides and oxides of chromium exhibit substantial differences in their crystallographic and electronic structure. The present study shows some of the possibilities for tuning the crystallographic and electronic properties of chromium oxynitride films by progressively increasing the oxygen concentration. We observe that upon oxygen addition the CrOxN1-x films remain in the face centered cubic B1 structure of CrN, up to oxygen contents of x ≤ 0.70. At higher oxygen concentrations they gradually adopt the properties of chromium sesquioxide and crystallize in the corundum Cr2O3 structure. The gradual decrease of the stress-free lattice parameter of the films with the B1 structure indicates that oxygen substitutes progressively for the nitrogen atoms. The (001) preferred orientation of the B1 films becomes more pronounced with the increase of oxygen concentration in the films. This trend is ascribed to the increased energy of the polar (111) planes with the substitution of nitrogen by the more electronegative oxygen anions. Changes in the core-level binding energies (BE) of the Cr 2p3/2 and N 1s observed by X-ray photoelectron spectroscopy (XPS) with increasing x indicate enhanced charge transfer from Cr to O with respect to N. A shift of the valence band edge toward higher BE suggests a decrease of electrical conductivity of the films with increasing oxygen content. [ABSTRACT FROM AUTHOR]

It is well known that surface energy differences thermodynamically stabilize nanocrystalline γ-Al 2 O 3 over α-Al 2 O 3 . Here, through correlative ab initio calculations and advanced material characterization at the nanometer scale, we demonstrate that the metastable phase formation of nanocrystalline TiAlN, an industrial benchmark coating material, is crystallite size-dependent. By relating calculated surface and volume energy contributions to the total energy, we predict the chemical composition-dependent phase boundary between the two metastable solid solution phases of cubic and wurzite Ti 1-x Al x N. This phase boundary is characterized by the critical crystallite size d critical . Crystallite size-dependent phase stability predictions are in very good agreement with experimental phase formation data where x was varied by utilizing combinatorial vapor phase condensation. The wide range of critical Al solubilities for metastable cubic Ti 1-x Al x N from x max  = 0.4 to 0.9 reported in literature and the sobering disagreement thereof with DFT predictions can at least in part be rationalized based on the here identified crystallite size-dependent metastable phase formation. Furthermore, it is evident that predictions of critical Al solubilities in metastable cubic TiAlN are flawed, if the previously overlooked surface energy contribution to the total energy is not considered.