A ternary Cr₂AlB₂ phase was deposited as a film using magnetron sputtering. Its anisotropic structure displays both structural and chemical similarities with the nanolaminated MAX phases (M_n+1AX_n (n = 1–3) where M usually is an early transition metal, A is typically an element in group 13–14 and X is C or N), and can be described as CrB slabs separated by layers of Al. Combinatorial sputtering was used to optimise the sputtering process parameters for films with the Cr₂AlB₂ composition. The influences of substrate, temperature and composition were studied using X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. Films deposited at room temperature were X-ray amorphous but crystalline films could be deposited on MgO substrates at 680 °C using a composite Al-B, Cr and Al targets. X-ray diffraction analyses showed that the phase composition and texture of the films was strongly dependent on the chemical composition. Films with several phases or with a single Cr₂AlB₂ phase could be deposited, but an additional Al target was required to compensate for a loss of Al at the high deposition temperatures used in this study. The microstructure evolution during film growth was strongly dependent on composition, with a change in texture in Al-rich films from a preferred [010] orientation to a [100]/[001] orientation. A model based on Al desorption from the surface of the growing grains is proposed to explain the texture variations.

High-temperature ceramic compound Al ₅ C ₃ N belongs to the scarcely studied Al–C–N system. It was originally reported as an ordered compound in noncentrosymmetric space group P 6 ₃ mc and described as a nanolaminate with an –Al ₂ C–AlN–Al ₂ C ₂ – stacking sequence. The recently reported structural disorder in the related compound Al ₄ SiC ₄ led us to question this proposed structure for Al ₅ C ₃ N and investigate the possibility of a disordered structure in the centrosymmetric space group P 6 ₃ / mmc . In the present work, we employed different synthesis routes to maximize the yield and quality of the desired phase, and applied a variety of techniques to probe the Al ₅ C ₃ N crystal structure. Our single-crystal X-ray diffraction analysis clearly indicates that noncentrosymmetric space group P 6 ₃ mc must be rejected. From a joint refinement of single-crystal X-ray and neutron powder diffraction data, the occupancies of C and N were refined at two sites in P 6 ₃ / mmc resulting in the stacking sequence –Al ₂ C–Al(C/N)–Al ₂ (C/N) ₂ –. Furthermore, DFT calculations show that a centrosymmetric disordered structure described in a supercell has the lowest energy, 0.2 eV per formula unit, relative to the previously reported P 6 ₃ mc structure. The calculated band structure shows both direct and indirect bandgaps, which leads to implications for the physical properties. Finally, STEM analysis provides additional evidence that the crystal structure of Al ₅ C ₃ N is better described in centrosymmetric space group P 6 ₃ / mmc .