Synthesis and structural characterization of a new aluminum oxycarbonitride, Al5(O, C, N)4

A new aluminum oxycarbonitride, Al₅(O_xC_yN_4−x−y) (x∼1.4 and y∼2.1), has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and electron energy loss spectroscopy (EELS). The title compound was found to be hexagonal with space group P6₃/mmc, Z=2, and unit-cell dimensions a=0.328455(6) nm, c=2.15998(3) nm and V=0.201805(6) nm³. The atom ratios O:C:N were determined by EELS. The final structural model, which is isomorphous with that of (Al_4.4Si_0.6)(O_1.0C_3.0), showed the positional disordering of one of the three types of Al sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R_wp=6.94% (S=1.22), R_p=5.34%, R_B=1.35% and R_F=0.76%. The crystal was an inversion twin. Each twin-related individual was isostructural with Al₅C₃N (space group P6₃mc, Z=2).